Dengue Regional Guidelines on Dengue DHF Prevention & Control Searo-29

Contents

PREFACE ..................................................................................................................... ix

ACKNOWLEDGEMENTS ................................................................................................. xi

1. INTRODUCTION ................................................................................................. 1

2. DENGUE AND DENGUE HAEMORRHAGIC FEVER ................................................. 32.1 Historical Overview .................................................................................... 32.2 The Virus ................................................................................................... 32.3 The Vector .................................................................................................. 42.4 The Host .................................................................................................... 42.5 Global Situation ......................................................................................... 42.6 Dengue/Dengue Haemorrhagic Fever in South-East Asia ................................ 52.7 Transmission Cycle ..................................................................................... 82.8 Epidemiological Pattern .............................................................................. 8

Virus-host interactions ................................................................................... 8Risk factors for DHF ..................................................................................... 9

3. CLINICAL MANIFESTATIONS AND DIAGNOSIS ...................................................... 113.1 Clinical Presentation ................................................................................. 11

Dengue fever ............................................................................................ 12Clinical Symptoms ...................................................................................... 12Clinical Laboratory Findings .......................................................................... 13Dengue haemorrhagic fever and dengue shock syndrome ................................ 13

3.2 Pathogenesis and Pathophysiology ............................................................. 153.3 Clinical Laboratory Findings of DHF ........................................................... 153.4 Criteria for Clinical Diagnosis of DHF/DSS ................................................. 16

Clinical Manifestations ................................................................................ 16Laboratory Findings ..................................................................................... 17

3.5 Grading the Severity of Dengue Haemorrhagic Fever ................................... 183.6 Differential Diagnosis of DHF .................................................................... 183.7 Complications and Unusual Manifestations of DF/DHF in Childhood ............ 183.8 Clinical Manifestations of DF/DHF in Adults ............................................... 19

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Comprehensive Guidelines for Prevention and Control of Dengue/DHF

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4. CLINICAL MANAGEMENT OF DF/DHF ................................................................. 214.1 Dengue Fever ........................................................................................... 214.2 Dengue Haemorrhagic Fever/Dengue Shock Syndrome ................................ 21

General considerations ................................................................................ 21Febrile phase ............................................................................................. 22Volume replacement in DHF ....................................................................... 23

4.3 Dengue Shock Syndrome ........................................................................... 25Immediate replacement of plasma................................................................ 25Other electrolyte and metabolic disturbances that may require specific correction .................................................................................... 27Sedatives .................................................................................................. 27Oxygen therapy ......................................................................................... 27Blood transfusion ....................................................................................... 27Essential laboratory tests .............................................................................. 28Monitoring and anti-shock therapy ................................................................ 28

4.4 Criteria for Discharging Patients Hospitalized with DHF/DSS ....................... 284.5 Management of Unusual Manifestations/Complications ............................... 294.6 DHF Special Unit...................................................................................... 294.7 Role of WHO Collaborating Centres .......................................................... 29

5. LABORATORY DIAGNOSIS ................................................................................. 315.1 Collection of Specimens ............................................................................ 31

Blood collection in tubes or vials .................................................................. 32Blood collection on filter paper .................................................................... 33

5.2 Isolation of Dengue Virus .......................................................................... 335.3 Serological Tests for the Diagnosis of DF/DHF ............................................ 34

Haemagglutination inhibition (HI) test ........................................................... 35Complement fixation (CF) test ..................................................................... 35Neutralization test (NT) ............................................................................... 36IgM-capture enzyme-linked immuno-sorbent assay (MAC-ELISA) ....................... 36IgG-ELISA .................................................................................................. 38Rapid serologic test kits ............................................................................... 38

6. EPIDEMIOLOGICAL SURVEILLANCE .................................................................... 396.1 Case Surveillance ..................................................................................... 39

Passive surveillance ..................................................................................... 39Active surveillance ...................................................................................... 41

6.2 Vector Surveillance ................................................................................... 42Larval surveys ............................................................................................ 42Adult surveys ............................................................................................. 44Oviposition traps ........................................................................................ 44Tyre section larvitraps .................................................................................. 45Epidemiological interpretations of vector surveillance ....................................... 45


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Adult surveillance ....................................................................................... 45Larval surveillance ....................................................................................... 46Sampling strategies ..................................................................................... 46Systematic sampling .................................................................................... 46Simple random sampling .............................................................................. 46Stratified random sampling ........................................................................... 46Frequency of sampling ................................................................................ 47Insecticide susceptibility testing .................................................................... 47Additional information for entomological surveillance ....................................... 47

7. VECTOR DISTRIBUTION AND BIOECOLOGY ...................................................... 497.1 Aedes aegypti .............................................................................................. 49

Taxonomic status ........................................................................................ 49Geographical distribution in South-East Asia .................................................... 49Ecology and bionomics ................................................................................ 50Eggs ......................................................................................................... 50Larvae and pupae ....................................................................................... 51Adults ....................................................................................................... 51Virus transmission ....................................................................................... 52

7.2 Aedes albopictus ....................................................................................... 527.3 Vector Identification .................................................................................. 52

8. PREVENTION AND CONTROL MEASURES ........................................................... 538.1 Environmental Management ...................................................................... 53

Environmental modification .......................................................................... 54Environmental manipulation ......................................................................... 54

8.2 Personal Protection ................................................................................... 57Protective clothing ...................................................................................... 57Mats, coils and aerosols ............................................................................... 57Repellents ................................................................................................. 57Insecticide-treated mosquito nets and curtains ................................................ 58

8.3 Biological Control ..................................................................................... 58Fish .......................................................................................................... 58Bacteria .................................................................................................... 58Cyclopoids ................................................................................................ 59Autocidal ovitraps ....................................................................................... 59

8.4 Chemical Control ...................................................................................... 59Chemical larviciding .................................................................................... 60Space sprays .............................................................................................. 61Performance of fogging machines ................................................................. 63Insecticide formulations for space sprays ........................................................ 63Integrated control approach ......................................................................... 64Insecticide susceptibility monitoring .............................................................. 64Safety precautions for chemical control .......................................................... 64


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9. SUSTAINABLE PREVENTION AND CONTROL MEASURES ..................................... 659.1 Community Participation ........................................................................... 65

Objectives of community participation in dengue prevention and control ........... 65How to invoke community participation ........................................................ 65Defining community actions ........................................................................ 66

9.2 Intersectoral Coordination ......................................................................... 67Resource sharing ........................................................................................ 67Policy adjustment ....................................................................................... 68Role of non-health sectors in dengue control .................................................. 68Role of nongovernmental organizations (NGOs) .............................................. 69

9.3 Model Development ................................................................................. 699.4 Social Mobilization ................................................................................... 709.5 Health Education ...................................................................................... 709.6 Legislative Support ................................................................................... 70

10. EVALUATION OF DF/DHF PREVENTION AND CONTROL PROGRAMMES .............. 7310.1 Types of Evaluation .................................................................................... 73

Monitoring ................................................................................................ 73Formal evaluation ....................................................................................... 74

10.2 Evaluation Plans ....................................................................................... 7410.3 Cost-Effective Evaluation ............................................................................ 75

11. THE REGIONAL STRATEGY FOR THE PREVENTION AND CONTROL OF DF/DHF ............................................................................. 8111.1 Basic Elements ......................................................................................... 81

Strategy requirements ................................................................................. 8111.2 National Dengue Control Programmes in South-East Asian Countries ............ 8211.3 Planning a Dengue Control Programme ...................................................... 82

Preparatory phase ....................................................................................... 83Planning phase ........................................................................................... 83Logistic support .......................................................................................... 84Implementation phase ................................................................................ 85Monitoring and evaluation ........................................................................... 85

12. EMERGENCY PREPEREDNESS AND EFFECTIVE RESPONSE .................................... 8712.1 Predictive Indicators ................................................................................. 87

Prediction of impending epidemics ............................................................... 8712.2 DF/DHF Epidemic Management ................................................................. 88

Administrative actions ................................................................................. 88Role and functions of public information, media and community ....................... 89Management of DF/DHF/DSS and laboratory services in hospitals during epidemics ......................................................................... 90Vector control for containment of epidemics .................................................. 93

Preface

T HROUGH the ages, dengue fever (DF) has been a cause of public healthconcern in the South-East Asia Region. After World War II, there was adramatic increase in the frequency and number of epidemics in South-

East Asia, with the emergence of the severe forms - dengue haemorrhagic fever(DHF) and dengue shock syndrome (DSS). Globally, 2.5 to 3 billion people areestimated to be at risk of infection with dengue viruses. Affecting mostly children,the case fatality rates range from less than 1% to 10% (average 5%).

Dengue haemorrhagic fever appeared for the first time in 1953 in thePhilippines and later spread to most countries in the WHO South-East Asia (SEA)and Western Pacific (WP) Regions. In 1964, these two Regions organized thefirst Interregional Seminar on Mosquito-borne Haemorrhagic Fevers in Bangkok,Thailand. Since then, the World Health Organization has been actively involvedin the planning, development, establishment and evaluation of dengue preventionand control programmes in endemic Member States.

In 1974, the two WHO Regions established a Technical Advisory Committeeon DHF. In view of the increasing occurrence of epidemics, it was felt thatguidelines for the diagnosis, treatment and control of dengue infection would bevery useful to the physicians and health authorities. The first version of the TechnicalGuide for Diagnosis, Surveillance, Prevention and Control of DengueHaemorrhagic Fever was published in 1975. The Regions also supported researchon the pathophysiology and clinical and laboratory diagnosis of dengue. On thebasis of these studies, revised guidelines on DHF were issued in 1980, 1986and 1998. Simultaneously, this effort was strengthened at the regional level bythe publication of technical guidelines by some WHO Regional offices.

Researchers and programme managers studying dengue in the South-EastAsia Region have demonstrated that different geographic areas show a variableresponse to the infection and accordingly, present different epidemiologicalpatterns. The complex epidemiology of DF/DHF may be further modified at thelocal level by different socioeconomic and sociocultural practices in the diverse

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communities of the Region. These epidemiological complexities call for specificsolutions for the prevention and control of DF/DHF.

The Comprehensive Guidelines for Prevention and Control of Dengue/DHFfocus on the South-East Asia Region. While the key roles of Ministries of Healthas well as the non-health sectors have been highlighted, emphasis has also beenplaced on community involvement particularly of students, welfare and civicorganizations and NGOs. This is essential to achieve acceptable levels of vectorcontrol through cost-effective and sustainable activities.

Epidemic preparedness is another important area which requires attention.Efforts to make communities self-reliant to meet the problems posed by denguein the domestic environment are essential.

It is hoped that these guidelines, drawn upon earlier guidelines andnumerous WHO and other publications will prove useful in effectively meetingthe challenge posed by DF/DHF in the Region.

Dr Uton Muchtar RafeiRegional Director

Acknowledgements

These guidelines on the prevention and control of dengue/dengue haemorrhagicfever were drafted by Mr Nand L. Kalra, Consultant Entomologist, Malaria ResearchCentre, Delhi. The draft document was reviewed by Prof D.H. Molyneus, Director,Liverpool School of Tropical Medicine, Liverpool, UK; Dr Duane J. Gubler, Director,Division of Vector Borne Infectious Diseases, CDC, Fort Collins, USA; Dr NormanG. Gratz, Entomologist and Specialist in Vector Biology and Control, Switzerland;Dr Andrew Arata, Senior Tropical Disease Specialist, Arlington, USA; Dr SuchitraNimmannitya, Consultant, Queen Sirikit National Institute of Child Health,Bangkok, Thailand; Dr Thomas Suroso, Director, VBDC, Jakarta, Indonesia; Dr SoeAung, Director, Communicable Diseases, Department of Health, Yangon,Myanmar; Dr Yongyuth Wangroongsarb, Senior Medical Officer, Department ofCommunicable Disease Control, Nonthaburi, Thailand; Mr Nand L. Kalra;Dr A.G. Andjaparidze, Regional Adviser, Communicable Diseases, WHO/SEARO,New Delhi; and Dr Chusak Prasittisuk, Regional Entomologist, WHO/SEARO,New Delhi.

Technical scrutiny of the final draft after incorporation of comments of thepeer group reviewers was undertaken by Dr Duane J. Gubler, and scientific editingwas carried out by Dr Chusak Prasittisuk, Regional Entomologist, WHO/SEARO,New Delhi and Ms C.M. Longmire, Technical Officer, Health Situation and TrendAssessment, WHO/SEARO, New Delhi.

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Introduction

DENGUE is caused by a virus spreadby Aedes (Stegomyia) mosquitoes.Over the past two decades there has

been a dramatic global increase in thefrequency of dengue fever (DF) denguehaemorrhagic fever (DHF), and dengue shocksyndrome (DSS) and their epidemics, with aconcomitant increase in disease incidence(Box 1). The World Health Report 1996 (1)

stated, that the “re-emergence of infectiousdiseases is a warning that progress achievedso far towards global security in health andprosperity may be wasted.” The report furtherindicated that “infectious diseases range fromthose occurring in tropical areas (such as malariaand DHF which are most common indeveloping countries) to diseases foundworldwide (such as hepatitis and sexuallytransmitted diseases, including HIV/AIDS) andfood-borne illnesses that affect large numbersof people in both the richer and poorernations.”

In May 1993, the 46th World HealthAssembly (WHA) adopted a resolution ondengue prevention and control which urgedthat the strengthening of national and localprogrammes for the prevention and control ofDF, DHF and DSS should be among thepriorities of WHO Member States where thedisease is endemic. The resolution alsorequested that: (1) strategies be developed to

Box IDengue and Dengue Haemorrhagic

Fever: Key Global Issues

l 2.5-3 billion people are at risk.l Aedes aegypti is the primary

epidemic vector.

l Imported cases are common.

l Urban disease, but becomingrural.

l Estimated 50-100 million cases ofdengue fever annually.

l 500,000 DHF cases requirehospitalization, each year of which90% are children less than 15years of age.

l Mortality averages 5% of DHFcases.

l Epidemics are cyclical.

contain the spread and increasing incidenceof dengue in a manner sustainable bycountries, (2) community health education beimproved, (3) health promotion beencouraged, (4) research be strengthened,(5) dengue surveillance be expanded,(6) guidance be given in vector control, and

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(7) the mobilization of external resources fordisease prevention be given a priority.

In response to the WHA resolution, ondengue prevention and control, a globalstrategy for operationalization of vector controlwas developed based on five majorcomponents (Box 2). One of the major pillarsof the global strategy is to increase active andaccurate laboratory-based surveillance for DF/DHF and its vectors. Effective surveillancerequires that DHF be made a reportable(notifiable) disease by all DF/DHF endemiccountries. These guidelines are based on theregional strategy developed in 1995, whichemphasizes disease surveil lance, casemanagement, integrated vector control andepidemic preparedness.

Box 2Global Strategy for Control

of DF/DHF Vectors

l Selective integrated mosquitocontrol with community andintersectoral participation

l Active disease surveillance based ona strong health information system

l Emergency preparedness

l Capacity building and training

l Research on vector control

Dengue and DengueHaemorrhagic Fever

2.1 Historical OverviewDengue epidemics are known to haveoccurred over the last three centuries intropical, subtropical and temperate areas ofthe world. The first epidemic of dengue wasrecorded in 1635(2) in the French West Indies,although a disease compatible with denguehad been reported in China as early as 992AD(3). During the 18th, 19th and early 20thcenturies, epidemics of dengue-like diseaseswere described globally in the tropics as wellas in some temperate regions. Rush(4) wasprobably describing dengue when he wroteof “break-bone fever” occurring inPhiladelphia in 1780. Most of these epidemicswere clinical dengue fever, although somewere associated with the severe haemorrhagicform of the disease. Efforts to control Aedesaegypti and economic development havemarkedly reduced the threat of epidemicdengue in temperate countries during the past50 years.

The first recorded outbreak of a denguedisease compatible with DHF occurred inAustralia in 1897. A similar haemorrhagic

disease was recorded in 1928 during anepidemic in Greece and again in Taiwan in1931. The first confirmed epidemic of DHFwas recorded in the Philippines in 1953-1954. Since then, major outbreaks of DHFwith significant mortality have occurred inmost countries of the South-East Asia Region,including India, Indonesia, Maldives,Myanmar, Sri Lanka, and Thailand, as well asin Singapore, Cambodia, China, Laos,Malaysia, New Caledonia, Palau, Philippines,Tahiti and Vietnam in the Western PacificRegion. Over the past 20 years, there hasbeen a dramatic increase in the incidence andgeographical distribution of DHF, andepidemics now occur each year in someSouth-East Asian countries.

2.2 The VirusThe dengue viruses are members of the genusFlavivirus and family Flaviviridae. These small(50 nm.) viruses contain single-strand RNA.The virion consists of a nucleocapsid withcubic symmetry enclosed in a lipoproteinenvelope. The dengue virus genome is

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approximately 11,000 base pairs in length,and is composed of three structural proteingenes encoding the nucleocaprid or coreprotein (C), a membrane-associated protein(M), an envelope protein (E), and sevennonstructural protein (NS) genes. Theenvelope glycoprotein is associated with viralhaemagglutination and neutralization activity.

The dengue viruses form a distinctcomplex within the genus Flavivirus based onantigenic and biological characteristics. Thereare four virus serotypes which are designatedas DEN-1, DEN-2, DEN-3 and DEN-4.Infection with any one serotype conferslifelong immunity to that virus serotype.Although all four serotypes are antigenicallysimilar, they are different enough to elicitcross-protection for only a few months afterinfection by any one of them.

Dengue viruses of all four serotypes havebeen associated with epidemics of denguefever in which there was little or no evidenceof DHF. All four virus serotypes have alsocaused DHF epidemics associated with severeand fatal disease.

2.3 The VectorDengue viruses are transmitted from person toperson by Aedes (Ae.) mosquitoes of thesubgenus Stegomyia. Ae. aegypti is the mostimportant epidemic vector, but other speciessuch as Ae. albopictus, Ae. polynesiensis,members of Ae. scutellaris complex, and Ae.(Finlaya) niveus have also been incriminated assecondary vectors. All except Ae. aegypti havetheir own restricted geographical distributionand, although they may be excellent hosts for

dengue viruses, they are generally less efficientepidemic vectors than Ae. aegypti.

2.4 The HostDengue viruses infect humans and severalspecies of lower primates. Humans are themain urban reservoir of the viruses. Studies inMalaysia and Africa have shown that monkeysare infected and are the likely reservoir hosts,although the epidemiological significance ofthis observation remains to be established(4,5,6).Dengue virus strains grow well in insect tissuecultures and on mammalian cell cultures afteradaptation.

2.5 Global SituationSignificant recent dengue outbreaks haveoccurred in five of the six WHO Regions,with the European Region being the onlyexception. However, imported dengue hasbeen reported in significant numbers inseveral countries of that Region. The globalpopulation at risk is estimated to range from2.5 to 3 billion individuals living mainly inurban areas in tropical and subtropicalregions. However, whi le dengue wasformerly thought to be strictly an urbanproblem, it is now recognized as also beingof significance in rural areas of South-EastAsia. It is estimated that there are at least100 million cases of dengue fever annuallyand 500,000 cases of DHF which requirehospitalization. Of the latter, 90% arechildren under the age of 15 years. DHFmorta l i ty ra tes average 5% , wi thapproximately 25,000 deaths each year(7).

Dengue and Dengue Haemorrhagic Fever

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Box 3The Global Problem of Dengue

Africa – 20 endemic countriesl Epidemics have been caused by all four virus

serotypes in the past 18 yearsl Recent major epidemic in the Comores

and Eritreal DHF not reported

Eastern Mediterranean – 4 endemiccountriesl Recent major epidemics in Dibouti, Saudi

Arabia and Pakistanl Multiple virus serotypes circulatingl Sporadic cases of DHF documented

Western Pacific – 29 endemic countriesl Recent major epidemics in Singapore,

Cambodia, Vietnam, Philippines, Tahiti,Fiji and Palau

l All four virus serotypes circulatingl DHF is endemic and is a major public

health problem in many countries

Americas – 42 endemic countriesl Recent major epidemics in Central

America, Colombia, Peru, Venezuela,Brazil, Mexico, Cuba, Puerto Rico,Barbados and Trinidad

l All four serotypes circulatingl DHF is a newly emergent disease and

now occurs in 24 countries

South-East Asia – 7 endemic countriesl Recent major epidemics in India, Sri

Lanka, Thailand, Myanmar and Indonesial All four virus serotypes circulatingl DHF is a leading cause of hospitalization

and death among children

The world distribution of DF/DHF hasrecently been reviewed(8). Between 1975 and1995, DF/DHF was present in 102 countriesof five WHO Regions: 20 countries in Africa,42 in the Americas, 7 in South-East Asia, 4 inthe Eastern Mediterranean, and 29 in theWestern Pacific (Box 3).

All tropical regions of the world havenow become hyperendemic, with all fourvirus serotypes circulating simultaneously inthe Americas, Asia, the Pacific and Africa(8).Northern Queens land, Austra l ia hasreported three serotypes (DEN-1, DEN-2and DEN-3) and the Middle East hasreported two serotypes (DEN-I and DEN-2).The current s i tuat ion of DF/DHF indifferent WHO Regions has been describedby Gratz and Knudsen (1996)(9) and Gubler(1998) (10). Factors responsible for theresurgence of dengue infect ion aresummarized in Box 4(10).

2.6 Dengue/DengueHaemorrhagic Fever inSouth-East Asia

The reported DHF cases and deaths between1985-1996 in the ten countries of the WHOSouth-East Asian Region are presented inTable 1. Boxes 5 and 6 and Figure 1underscore the public health importance ofthis disease in the Region, which continues tobe hyperendemic. The number of cases haveincreased over the last three to five years, withrecurring epidemics. Moreover, there hasbeen an increase in the proportion of denguecases with severe disease, particularly in India,Sri Lanka and Myanmar.


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Box 4Factors Responsible for the Resurgence

of the Dengue Epidemic

l Unprecedented human populationgrowth

l Unplanned and uncontrolledurbanization

l Inadequate waste management andwater supply

l Increased distribution and densities ofvector mosquitoes

l Lack of effective mosquito controll Increased movement and spread of

dengue virusesl Development of hyperendemicityl Deterioration in public health

infrastructure

Box 5Dengue Haemorrhagic Fever as a

Major Public Health Problemin South-East Asia

l Seven of the ten countries have a seriousDHF problem.

l DHF is a leading cause of hospitali-zation and death among children inthese countries.

l The incidence of DHF in the Region hasincreased dramatically in the past 17years; and approximately five timesmore cases have been reported since1980 than in the previous 30 years.

l The geographic distribution hasexpanded within countries as well as tonew countries in the Region.

Box 6Stratification of Dengue / Dengue

Haemorrhagic Fever in theSouth-East Asia Region

Category A (Indonesia, Myanmar,Thailand)

l Major public health probleml Leading cause of hospitalization and

death among childrenl Cyclical epidemics in urban centres

with 3-5 year periodicityl Spreading to rural areasl Multiple virus serotypes circulatingl Aedes aegypti is the principal

epidemic vectorl Role of Aedes albopictus is uncertain

Category B (Bangladesh, India,Maldives, Sri Lanka)

l DHF is an emergent diseasel Cyclical epidemics are becoming

more frequentl Multiple virus serotypes circulatingl Expanding geographically within

countriesl Aedes aegypti is the principal

epidemic vectorl Role of Aedes albopictus is uncertain

Category C (Bhutan, Nepal)

l No reported cases

l Endemicity uncertain

Category D (DPR Korea)

l Non-endemic


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Table 1. Number of Reported Cases and Deaths of DF andDHF in the South-East Asia Region

By Country, Years 1985-97

Country Ind ia Indonesia Maldives M y a n m a r Sri Lanka Thai land Total

Case 13 588 2 666 80 076 96 3301985 Death NA 460 NA 134 NA 542 1 136

CFR (%) 3.39 5.03 0.68 1.18

Case 16 529 2 092 27 837 46 4581986 Death NA 608 NA 111 NA 236 955

CFR (%) 3.68 5.31 0.85 2.06

Case 23 864 7 231 174 285 205 3801987 Death NA 1 105 NA 227 NA 1 007 2 339

CFR(%) 4.63 3.14 0.58 1.14

Case 44 573 2 054 1 178 10 26 925 74 7411988 Death NA 1 527 9 64 0 179 1 779

CFR(%) 3.43 0.43 5.43 0.00 0.636 2.38

Case 10 362 1 196 203 74 391 86 1521989 Death NA 464 NA 62 20 290 836

CFR(%) 4.48 5.18 9.85 0.39 0.97

Case 22 807 5 242 1 350 92 002 121 4011990 Death NA 821 NA 179 54 414 1468

CFR(%) 3.60 3.41 4.00 0.44 1.21

Case 6 291 21 120 6 772 1048 43 511 78 7421991 Death 3 578 NA 282 31 137 1 031

CFR(%) 0.05 2.74 4.16 2.96 0.31 1.31

Case 2 683 17 620 1 685 656 41 125 63 7691992 Death 12 509 NA 37 15 136 709

CFR(%) 0.45 2.89 2.20 2.29 0.33 1.11

Case 11 125 17 418 2 279 750 67 017 98 5891993 Death 36 418 NA 67 7 222 750

CFR(%) 0.32 2.40 2.94 0.93 0.33 0.76

Case 7 494 18 783 11 647 582 51 688 90 1941994 Death 4 471 NA 461 7 140 1 083

CFR(%) 0.05 2.51 3.96 1.20 0.27 1.20

Case 7 847 35 102 2 477 440 59 911 105 7771995 Death 10 885 NA 53 11 183 1 142

CFR(%) 0.13 2.52 2.14 2.50 0.31 1.08

Case 16 517 44 650 1 655 1 298 38 109 102 2291996 Death 545 1 192 NA 18 54 114 1 923

CFR(%) 3.30 2.67 1.09 4.16 0.30 1.88

Case 1 177 30 730 3 993 980 99 150 136 0301997 Death 36 681 NA 76 17 227 1 037

CFR(%) 3.05 2.22 1.90 1.73 0.27 0.76

NA: Not available


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Figure 1 Number of Reported Cases and Case Fatality Rate of DF/DHFin the South-East Asia Region, 1985-1997

0

50,000

100,000

150,000

200,000

250,000

0

0.5

1

1.5

2

2.5

CFR% Cases

2.7 Transmission CycleThe female Aedes (Stegomyia ) mosquitousually becomes infected with dengue viruswhen she takes blood from a person duringthe acute febrile (viraemic) phase of illness(Box 7). After an extrinsic incubation periodof 8 to 10 days, the salivary glands of themosquito become infected and the virus istransmitted when the infective mosquito bitesand injects the salivary fluid into the woundof another person. Following an incubationperiod in humans of 3-14 days (4-6 daysaverage), there is often a sudden onset of thedisease, with fever, headache, myalgias, lossof appetite, and a variety of nonspecific signsand symptoms, including nausea, vomitingand rash.

Viraemia is usually present at the time ofor just before the onset of symptoms and lastsan average of five days after the onset of

illness. This is the crucial period when thepatient is most infective for the vectormosquito and contributes to maintaining thetransmission cycle if the patient is notprotected against vector mosquito bites.

There is evidence that the verticaltransmission of dengue virus from infectedfemale mosquitoes to the next generationoccurs in several species including Ae. aegyptiand Ae. albopictus (11). This may be animportant mechanism for virus maintenance,but does not appear to be important inepidemics(10,11).

2.8 Epidemiological PatternVirus-host interactions

In order to understand the variousepidemiological situations, it is important to

85 86 87 88 89 90 91 92 93 94 95 96 97

Cas

es

CFR

(%)

Year


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Box 7Transmission Cycle

l Vectors: Aedes aegypti, otherAedes (Stegomyia) spp.

l Extrinsic incubation period 8-10days

l Dengue virus infection in personfrom mosquito bite

l Intrinsic incubation 3-14 days(Average 4-7 days)

l Viraemia appears before theonset of symptoms and lasts anaverage of five days after theonset

l Possible vertical transmission,which may be important in virusmaintenance, but not in epidemiccycles

Box 8Risk Factors For Dengue

Haemorrhagic Fever

l Immune status of individualsl Infecting virus strain/serotypel Age of patientl Genetic background of patient

recognize the fundamental aspects of virus-host interaction. These are:l Dengue infection frequently causes mild

illness in children.l Dengue infection in adults frequently

produces symptoms, with the infection:apparent illness ratio approaching 1 insome epidemics. Some virus strains,however, produce very mild illness in bothadults and children which is often notrecognized as dengue and circulatessilently in the community.

l Primary as well as secondary dengueinfections in adults may result in severegastrointestinal haemorrhage, as well ascases with increased vascularpermeability. For example, many adultswith severe haemorrhage associated withDEN-1 in Taiwan in 1988 had underlyingpeptic ulcer disease.

Risk factors for DHF

Secondary dengue infection is a risk factor forDHF, including passively-acquired antibodiesin infants. The strain of virus is also a risk factorfor DHF; not all wild type viruses haveepidemic potential or cause severe disease(Box 8). Finally, the age of the patient and hostgenetics are risk factors of DHF. Although DHFcan and does occur in adults, most cases arein children less than 15 years of age, andcircumstantial evidence suggests that somepopulation groups may be more susceptibleto vascular leak syndrome than others.

Clinical Manifestationsand Diagnosis

3.1 Clinical Presentation

Dengue virus infection may be asymptomaticor may cause undifferentiated febrile illness(viral syndrome), dengue fever (DF), or denguehaemorrhagic fever (DHF) including dengueshock syndrome (DSS). Infection with onedengue serotype gives lifelong immunity to

that particular serotype, but there is no cross-protection for the other serotypes. The clinicalpresentation depends on age, immune statusof the host, and the virus strain (Box 9).(i) Undifferentiated fever: Infants, childrenand some adults who have been infected withdengue virus for the first time (i.e. primarydengue infection) will develop a simple fever

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Box 9Manifestation of Dengue Infection

Dengue Virus Infection

Dengue haemorrhagicfever

Dengue fever

Undifferentiated fever

AsymptomaticWithout

haemorrhage

With unusualhaemorrhage

No shock

Dengue shocksyndrome (DSS)

Symptomatic


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indistinguishable from other viral infections.Maculopapular rashes may accompany thefever or may appear during defervescence.(ii) Dengue fever: Dengue fever is mostcommon in older children and adults. It isgenerally an acute biphasic fever withheadache, myalgias, arthralgias, rashes andleucopenia. Although DF is commonly benign,it may be an incapacitating disease withsevere muscle and joint pain (break-bonefever), particularly in adults, and occasionallywith unusual haemorrhage. In dengueendemic areas, DF seldom occurs amongindigenous people.(iii) Dengue haemorrhagic fever: Denguehaemorrhagic fever is most common inchildren less than 15 years of age, but it alsooccurs in adults. DHF is characterized by theacute onset of fever and associated non-specific constitutional signs and symptoms.There is a haemorrhagic diathesis and atendency to develop fatal shock (dengueshock syndrome). Abnormal haemostasis andplasma leakage are the main patho-physiological changes, with thrombocytopeniaand haemoconcentration presenting asconstant findings. Although DHF occurs mostcommonly in children who have experiencedsecondary dengue infection, it has also beendocumented in primary infections.

Dengue fever

Clinical Symptoms

After an average incubation period of 4-6 days(range 3-14 days), various non-specific,undifferentiated prodomes, such as headache,

backache and general malaise may develop.Typically, the onset of DF in adults is sudden,with a sharp rise in temperature occasionallyaccompanied by chillis, and is invariablyassociated with severe headache and flushedface(12). Within 24 hours there may be retro-orbital pain, particularly on eye movement oreye pressure, photophobia, backache andpain in the muscles and joints/bones of theextremities. The other common symptomsinclude anorexia and altered taste sensation,constipation, colicky pain and abdominaltenderness, dragging pains in the inguinalregion, sore throat, and general depression.These symptoms vary in severity and usuallypersist for several days.Fever: The body temperature is usuallybetween 39oC and 40oC, and the fever maybe biphasic, lasting 5-7 days.Rash: Diffuse flushing or fleeting pinpointeruptions may be observed on the face, neckand chest during the first half of the febrileperiod, and a conspicuous rash that may bemaculopapular or scarlatiniform appears onapproximately the third or fourth day. Towardsthe end of the febrile period or immediatelyafter defervescence, the generalized rash fadesand localized clusters of petechiae mayappear over the dorsum of the feet, on thelegs, and on the hands and arms. Thisconfluent petechial rash is characterized byscattered, pale, round areas of normal skin.Occasionally the rash is accompanied byitching.Skin Haemorrhage: A positive tourinquet testand/or petechiae.Course: The relative duration and severity ofDF varies between individuals in a given

Clinical Manifestations and Diagnosis

13

epidemic, as well as from one epidemic toanother. Convalescence may be short anduneventful, but may also often be prolonged.In adults it sometimes lasts for several weeksand may be accompanied by pronouncedasthenia and depression. Bradycardia iscommon during convalescene. Haemorrhagiccomplications, such as epistaxis, gingivalbleeding, gastrointestinal bleeding,haematuria and hypermenorrhoea, mayaccompany epidemics of DF. Severe bleedinghas occasionally caused deaths in someepidemics. Dengue fever with haemorrhagicmanifestations must be differentiated fromdengue haemorrhagic fever.

Clinical Laboratory Findings

The laboratory findings during an acute DFepisode of illness are as follows:l Total WBC is usually normal at the onset

of fever; then leucopenia develops andlasts throughout the febrile period.

l Platelet counts are usually normal, as areother components of the blood clottingmechanism. However, thrombocytopeniais common in some epidemics.

l Serum biochemistry and enzymes areusually normal, but liver enzyme levelsmay be elevated.

Differential Diagnosis: The differentialdiagnoses associated with DF include a widevariety of viral (including chikungunya),bacterial, rickettsial and parasitic infectionsthat produce a similar syndrome. It isimpossible to diagnose mild dengue infectionclinically, particularly when there are onlysporadic cases. A definitive diagnosis isconfirmed by virus isolation and/or serology.

Dengue haemorrhagic fever and dengueshock syndrome

Typical cases of DHF are characterized byhigh fever, haemorrhagic phenomena,hepatomegaly, and often circulatory fail-ure (12,13). Moderate to marked thrombocytope-nia with concurrent haemoconcentration aredistinctive clinical laboratory findings. Themajor pathophysiologic changes that deter-mine the severity of the disease in DHF anddifferentiate it from DF are abnormalhaemostasis and leakage of plasma as mani-fested by thrombocytopenia and risinghaematocrit.

DHF commonly begins with a suddenrise in temperature which is accompanied byfacial flush and other non-specificconstitutional symptoms resembling denguefever, such as anorexia, vomiting, headache,and muscle or joint pains (Table 2) (14).

Some DHF patients complain of sorethroat, and an injected pharynx may be foundon examination. Epigastric discomfort,tenderness at the right costal margin, andgeneralized abdominal pain are common. Thetemperature is typically high and in most casescontinues for two to seven days, then falls toa normal or subnormal level. Occasionally thetemperature may be as high as 40oC, andfebrile convulsions may occur.

The most common haemorrhagicphenomenon is a positive tourniquet test. Easybruising and bleeding at venipuncture sites arepresent in most cases. Fine petechiaescattered on the extremities, axillae, face andsoft palate may be seen during the earlyfebrile phase. A confluent petechial rash with


14

characteristic small, round areas of normalskin is sometimes seen in convalescence afterthe temperature has returned to normal. Amaculopapular or rubella-type rash may beobserved early or late in the disease. Epistaxisand gum bleeding are less common. Mildgastrointestinal haemorrhage is occasionallyobserved. Haematuria is rarely observed.

The liver is usually palpable early in thefebrile phase, varying from just palpable to2-4 cm below the right costal margin. Liversize is not correlated with disease severity, but

hepatomegaly is more frequent in shock cases.The liver is tender, but jaundice is not usuallyobserved, even in patients with an enlarged,tender l iver. In some epidemics,hepatomegaly is not a consistent finding.Splenomegaly is rarely observed in infantsunder six months, however, the spleen issometimes prominent on X-ray examination.Chest X-rays show/reveal pleural effusion,mostly on the right side, as a constant finding.The extent of pleural effusion is positivelycorrelated with disease serverity.

In mild or moderate cases, all signs andsymptoms abate after the fever subsides. Feverlysis may be accompanied by profusesweating and mild changes in pulse rate andblood pressure, together with coolness of theextremities and skin congestion. Thesechanges reflect mild and transient circulatorydisturbances as a result of some degree ofplasma leakage. Patients usually recover eitherspontaneously or after fluid and electrolytetherapy.

In severe cases, the patient’s conditionsuddenly deteriorates a few days after onsetof fever. At the time of or shortly after thetemperature drop, between three and sevendays after the onset, there are signs ofcirculatory failure: the skin becomes cool,blotchy and congested, circumoral cyanosis isfrequently observed, and the pulse becomesweak and rapid. Although some patients mayappear lethargic, they become restless andthen rapidly go into a critical stage of shock.Acute abdominal pain is a frequent complaintshortly before the onset of shock.

The early stage of shock is characterizedby a rapid and weak pulse with narrowing of

Table 2. Non-specific constitutional symptomsobserved in haemorrhagic fever patients

with dengue and chikungunyavirus infectiona

DHF Chikun-Symptom (%) gunya

fever (%)

Injected pharynx 98.9 90.3Vomiting 57.9 59.4Constipation 53.3 40.0Abdominal pain 50.0 31.6Headache 44.6 68.4Generalized lymphadenopathy 40.5 30.8Conjunctival injection 32.8b 55.6b

Cough 21.5 23.3Restlessness 21.5 33.3Rhinitis 12.8 6.5Maculopapular rash 12.1b 59.6b

Myalgia/arthralgia 12.0b 40.0b

Enanthema 8.3 11.1Abnormal reflex 6.7 0.0Diarrhoea 6.4 15.6Palpable spleen (in infants < 6 months) 6.3 3.1Coma 3.0 0.0

a Based on: Nimmannitya S, et al, American Journal ofTropical Medicine and Hygiene, 1969, 18:954-971

b Statistically significant difference


15

the pulse pressure ≤ 20 mmHg, with a minimaldifference between systolic and diastolic bloodpressure levels, e.g (100/90) or hypotension,with cold clammy skin and restlessness. Patientsin shock are in danger of dieing if they do notpromptly get appropriate treatment. Patientsmay pass into a stage of profound shock withblood pressure and/or pulse becomingimperceptible. Most patients remain consciousalmost to the terminal stage. Shock lasts for ashort time; the patient may die within 12 to 24hours, or recover rapidly following appropriatevolume-replacement therapy. Alternatively,uncorrected shock may give rise to a morecomplicated course with metabolic acidosis,severe bleeding from the gastrointestinal tractas well as from various other organs, and a poorprognosis. Patients with intracranialhaemorrhage may have convulsions and go intocoma. Encephalopathy may occur in associationwith metabolic and electrolyte disturbances.

Convalescence in DHF with or withoutshock is short and uneventful. Even in caseswith profound shock, once the shock isovercome, the surviving patients recoverwithin two to three days. The return ofappetite is a good prognostic sign. Commonfindings in convalescence include sinusbradycardia or arrythmia and thecharacteristic dengue confluent petechial rashas described for DF.

3.2 Pathogenesis andPathophysiology

The pathogenesis of DHF is not fullyunderstood, but two main pathophysiologicchanges occur:

l Increased vascular permeability resultingin plasma leakage, hypovolaemia andshock. DHF appears unique in that thereis selective leakage of plasma into thepleural and peritoneal cavities and theperiod of leakage is short (24-48 hours).

l Abnormal haemostasis due tovasculopathy, thrombocytopenia andcoagulopathy, leading to varioushaemorrhagic manifestations.Activation of the complement system is

a constant finding in patients with DHF. Levelsof C3 and C5 are depressed, and C3a andC5a are elevated. The mechanisms ofcomplement activation are not known. Thepresence of immune complexes has beenreported in DHF cases, however, thecontribution of antigen-antibody complexes tocomplement activation in patients with DHFhas not been demonstrated.

It has been hypothesized that the severityof DHF compared with DF is explained by theenhancement of virus multiplication inmacrophages by heterotypic antibodiesresulting from a previous dengue infection.There is evidence, however, that viral factorsand a cell-mediated immune response arealso involved in the pathogenesis of DHF.

3.3 Clinical Laboratory Findingsof DHF

The laboratory findings in DHF are as follows:

l The WBC may be normal, but leucopeniais common initially, with neutrophilspredominating. Towards the end of thefebrile phase there is a drop in the totalnumber of white cells as well as in the


16

number of polymorphonuclear cells. Arelative lymphocytosis with more than15% atypical lymphocytes is commonlyobserved towards the end of the febrilephase (critical stage) and at the early stageof shock.

l Thrombocytopenia and haemo-concentration are constant findings inDHF. A drop in platelet count to below100,000/mm3 is usually found betweenthe third and eighth days of illness. A risein haematocrit occurs in all DHF cases,particularly in shock cases. Haemo-concentration with haematocrit increasedby 20% or more is considered objectiveevidence of increased vascularpermeability and leakage of plasma. Itshould be noted that the level ofhaematocrit may be affected by earlyvolume replacement and by bleeding.

l A transient mild albuminuria is sometimesobserved.

l Occult blood is often found in the stool.l In most cases, assays of coagulation and

fibrinolytic factors show reductions infibrinogen, prothrombin, factor VIII, factorXII, and antithrombin III. A reduction inantiplasmin (plasmin inhibitor) has beennoted in some cases. In severe cases withmarked liver dysfunction, reduction isobserved in the vitamin K-dependentprothrombin family, such as factors V, VII,IX and X.

l Partial thromboplastin time andprothrombin time are prolonged in about

one-half and one-third of DHF casesrespectively. Thrombin time is alsoprolonged in severe cases.

l Serum complement levels are reduced.l Other common findings are

hypoproteinemia, hyponatremia, andmildly elevated serum aspartateaminotransferase levels. Metabolicacidosis is frequently found in cases withprolonged shock. Blood urea nitrogen iselevated in the terminal stage of cases withprolonged shock.

3.4 Criteria for ClinicalDiagnosis of DHF/DSS

Clinical Manifestations:

l Fever: acute onset, high and continuous,lasting 2 to 7 days.

l Any of the following haemorrhagicmanifestations (including at least a positivetourniquet test*): petechiae, purpura,ecchymosis, epistaxis, gum bleeding, andhaematemesis and/or melena.– Enlargement of the liver (hepatomegaly)

is observed at some stage of the illnessin 90-98% of Thai children, but itsfrequency may be variable in othercountries.

– Shock, manifested by rapid and weakpulse with narrowing of the pulsepressure (20mm Hg or less), orhypotension, with the presence of cold,clammy skin and restlessness.

____________________________* The tourniquet test is performed by inflating a blood pressure cuff to a point midway between the systolic and

diastolic pressures for five minutes. The test is considered positive when 10 or more petechiae per 2.5 cm2 (1 squareinch) are observed. In DHF the test usually gives a definite positive result with 20 petechiae or more. The test may benegative or only mildly positive during the phase of profound shock. It usually becomes positive, sometimes stronglypositive, if it is conducted after recovery from shock.


17

Laboratory Findings:

– Thrombocytopenia (100,000/mm3 orless).*

– Haemoconcentration; haematocritincreased by 20% or more.

The first two clinical criteria, plusthrombocytopenia and haemoconcentrationor a rising haematocrit, are sufficient toestablish a clinical diagnosis of DHF. Pleuraleffusion (seen on chest X-ray) and/orhypoalbuminaemia provide supporting

evidence of plasma leakage. This is particularlyuseful in those patients who are anaemic and/or having severe haemorrhage. In cases withshock, a high haematocrit and markedthrombocytopenia support the diagnosis ofDHF/DSS.

The physical and laboratory findingsassociated with the various grades of severityof DHF are shown in Box 10 (see section 3.5for a description of the DHF severity grades).

____________________________* Direct count using a phase-contrast microscope (normal 200,000-500,000/mm3). In practice, for outpatients, an

approximate count from a peripheral blood smear is acceptable. In normal persons, 4-10 platelets per oil-immersionfield (the average observed from 10 fields is recommended) indicate an adequate platelet count. An average of2-3 platelets per oil-immersion field or less is considered low (less than 100,000/mm3).

Box 10The Spectrum of Dengue Haemorrhagic Fever

Source: Dengue haemorrhagic fever - Diagnosis, treatment, prevention and control, 2nd edition. World Health Organization, Geneva(14)

Grade IV

Grade III

Grade II

Grade IFever Positivetourniquet test

Increased vascularpermeabi l i ty Hepatomegaly Thrombocytopenia

Other haemorrhagicmanifestations

Hypovolaemia

Death

Coagulopathy

Severe bleeding

Rising haematocritHypoproteinaemiaSerous effusion

Leakageof plasma}

ShockDisseminatedintravascularcoagulation

Dengue Infection


18

3.5 Grading the Severity ofDengue Haemorrhagic Fever

The severity of DHF is classified into fourgrades(12,13) (Box 11).

The presence of thrombocytopenia withconcurrent haemoconcentration differentiatesGrade I and Grade II DHF from dengue fever.

Grading the severity of the disease hasbeen found clinically and epidemiologicallyuseful in DHF epidemics in children in theSouth-East Asia, Western Pacific, andAmerican Regions of WHO. Experiences inCuba, Puerto Rico and Venezuela suggest thatthis classification is also useful for adults.

3.6 Differential Diagnosis ofDHF

Early in the febrile phase, the differentialdiagnoses associated with DHF include a widespectrum of viral, bacterial, and protozoalinfections. Diseases such as leptospirosis,malaria, infectious hepatitis, chikungunya,meningococcaemia, rubella and influenzashould be considered. The presence ofmarked thrombocytopenia with concurrenthaemoconcentration differentiates DHF/DSSfrom other diseases. In patients with severebleeding, evidence of pleural effusion and/orhypoproteinemia indicates plasma leakage. Anormal erythrosedimentation rate in DHF/DSShelps to differentiate this disease frombacterial infection and septic shock.

3.7 Complications and UnusualManifestations of DF/DHFin Childhood

Encephalitic signs such as convulsion andcoma are rare in DHF. They may, however,occur as a complication in cases of prolongedshock with severe bleeding in various organsincluding the brain. Water intoxication, as aresult of inappropriate use of hypotonicsolution to treat DHF patients withhyponatraemia, is a relatively commoniatrogenic complication that leads toencephalopathy. A subtle form of seizure isoccasionally observed in infants under one yearof age during the febrile phase and, in somecases, is considered to be febrile convulsionssince the cerebrospinal fluid is normal. Subduraleffusions have been observed in some cases.

In recent years there has been anincreasing number of reports of DF or DHF

Box 11Grading the Severity of DHF

Grade I Fever accompanied by non-specific constitutionalsymptoms; the onlyhaemorrhagic manifestation isa positive tourniquet test.

Grade II Spontaneous bleeding inaddition to the manifestationsof Grade I patients, usually inthe form of skin and/or otherhaemorrhages.

Grade III Circulatory failure manifestedby rapid and weak pulse,narrowing of pulse pressure(20 mmHg or less) orhypotension, with thepresence of cold clammy skinand restlessness.

Grade IV Profound shock withundetectable blood pressureand pulse.


19

with unusual manifestations. Unusual centralnervous system manifestations, includingconvulsions, spasticity, change inconsciousness and transient paresis, havebeen observed. Some of these cases may haveencephalopathy as a complication of DHFwith severe disseminated intravascularcoagulation that may lead to focal occlusionor haemorrhage.

Fatal cases with encephalitic manifes-tations have been reported in Indonesia,Malaysia, Myanmar, India and Puerto Rico.However, in most cases there have been noautopsies to rule out bleeding or occlusion ofthe blood vessels. Although limited, there issome evidence that, on rare occasions,dengue viruses may cross the blood-brainbarrier and infect the CNS. Further studies areneeded to identify the factors contributing tothese unusual manifestations. Attention shouldbe given to the study of underlying host factorssuch as convulsive disorders and concurrentdiseases.

Encephalopathy associated with acuteliver failure is commonly observed and renalfailure usually occurs at the terminal stage.Liver enzymes are markedly elevated in thesecases, with serum aspartate aminotransferaseabout 2-3 times higher than serum alanineaminotransferase.

Other rarely observed, unusual manifes-tations of DF/DHF include acute renal failureand haemolytic uraemic syndrome. Some ofthese cases have been observed in patientswith underlying host factors (e.g. G6Pdeficiency and haemoglobinopathy) that leadto intravascular haemolysis. Dual infections

with other endemic diseases, such asleptospirosis, viral hepatitis B, and melioidosis,have been reported in cases with unusualmanifestations.

3.8 Clinical Manifestations ofDF/DHF in Adults

Cuba’s experience in 1981, with 130 adultcases (26 with fatal outcome), showed that theinfection was usually manifested by theclinical symptoms of dengue fever (high fever,nausea/vomiting, retro-orbital headache,myalgias and asthenia), regardless of whetherthe patient had a fatal outcome or not. Lessfrequently, patients demonstratedthrombocytopenia and haemorrhagicmanifestations, the most common of whichwere skin haemorrhages, menorrhagia, andhaematemesis. Overt shock in adults was lessfrequently observed than in children, but wassevere when it did occur. It was found mostlyin white adults with a history of bronchialasthma and other chronic diseases. In oneseries of 1,000 adult cases studied in Cuba,the persons who were severely ill usuallyshowed thrombocytopenia andhaemoconcentration. In five cases withhypovolemic shock not associated withhaemorrhage, the disease responded, as inchildren, to vigorous fluid replacement(15). Inthe 1986 Puerto Rico outbreak, DHF withovert shock in adults was not rare, but didoccur less frequently than in children(16).Similar observations were reported in therecent outbreak in New Delhi, India in1996(17).

Clinical Managementof DF/DHF

l Oral fluids and electrolyte therapy arerecommended for patients with excessivesweating or vomiting.In DHF-endemic areas, patients should

be monitored until after they become afebrileand after platelet counts and haematocritdeterminations are normal.

4.2 Dengue Haemorrhagic Fever/Dengue Shock Syndrome

General considerations

The major pathophysiologic hallmarks thatdistinguish DHF/DSS from DF and otherdiseases are abnormal haemostasis andincreased vascular permeability that lead toleakage of plasma. The clinical features ofDHF/DSS are rather stereotyped, with acuteonset of high (continuous) fever, haemorrhagicdiathesis (most frequently on the skin),hepatomegaly, and circulatory disturbance (inthe most severe form as shock). It is thuspossible to make an early and yet accurateclinical diagnosis of DHF/DSS before thecritical stage or before shock occurs, by using

21

EFFECTIVE case management of DF/DHFrequires well-trained physicians andnurses, modern state-of-the-art and

reliable laboratory facilities, functioningpharmacies and adequate blood supplysystems. Early diagnosis of the disease andadmission of patients to hospital are thereforeimportant in order to reduce case fatalityrates. Depending upon the severity ofinfection, three disease entities – DF, DHF andDSS – are recognized. The treatment of eachof these is discussed below.

4.1 Dengue FeverThe management of DF is symptomatic andsupportive.l Bed rest is advisable during the acute

febrile phase.l Antipyretics or sponging are required to

keep the body temperature below 40oC.Aspirin should be avoided since it maycause gastritis, bleeding and acidosis;paracetamol is preferable.

l Analgesics or mild sedatives may berequired for patients with severe pain.

E

4


22

the pattern of clinical presentations togetherwith thrombocytopenia and concurrenthaemoconcentration, which representabnormal haemostasis and plasma leakagerespectively.

The prognosis of DHF depends on earlyrecognition of plasma leakage. This can beachieved by frequent monitoring for a drop inthe platelet count and a rise in the haematocritlevel. The critical period is at the time ofdefervescence which occurs approximately onor after the third day of illness. A drop in theplatelet count to <100,000/mm3 or less than1-2 platelets per oil-immersion field (average of10 oil-immersion field counts), usually precedesa rise in haematocrit and may occur beforedefervescence. A rise in haematocrit of 20% ormore (e.g. increase from 35% to 42%) reflectsa significant plasma loss and indicates the needfor intravenous fluid therapy. Early volumereplacement of lost plasma with isotonic saltsolution can modify the severity of disease andprevent shock.

In mild to moderate cases of DHF(Grades I and II), intravenous fluid therapymay be given for a period of 12-24 hours atan outpatient clinic. Patients who continue tohave elevated haematocrit, platelet countsbelow 50,000/mm3, or present with any typeof spontaneous haemorrhage other thanpetechiae should be hospitalized. In general,there is no need to hospitalize all patients withsuspected DHF, since only about one-thirdwill develop shock.

Febrile phase

The management of DHF during the febrilephase is similar to that of DF. Antipyretics maybe indicated but salicylates should beavoided. It should be noted that antipyreticsdo not shorten the duration of fever in DHF.Paracetamol is recommended and should beused only to keep the temperature below39oC. The following dosages arerecommended: under-one year old: 60 mg/dose; 1-2 years old: 60-120 mg/dose; 3-6years old: 120 mg/dose; and 7-12 years old:240 mg/dose. Patients with hyperpyrexia areat risk of convulsions.

High fever, anorexia and vomiting lead tothirst and dehydration. Therefore, copiousamounts of fluids should be given orally, to theextent tolerated. Oral rehydration solutions,such as those used for the treatment ofdiarrhoeal diseases* and/or fruit juices arepreferable to plain water.

Patients should be closely monitored forthe initial signs of shock. The critical periodis during the transition from the febrile to theafebrile phase, and usually occurs after thethird day. Serial haematocrit determinationsare an essential guide for treatment, since theyreflect the degree of plasma leakage and theneed for intravenous administration of fluids.Haemoconcentration usually precedes theblood pressure and pulse changes. Haematocritshould be determined daily from the thirdday, until the temperature has remainednormal for one or two days. If haematocrit

____________________________* If the WHO oral rehydration solution (ORS) (90 mmol of Na per litre) is to be used in children under two years of age,

additional fruit juice or water should be given in the proportion of one volume of fruit juice (or water) for each twovolumes of ORS. The WHO oral rehydration solution consists of: 3.5 g sodium chloride, 2.9 g trisodium citratedihydrate, 1.5 g potassium chloride, and 20.0 g glucose, dissolved in 1 litre of potable water.

Clinical Management of DF/DHF

23

determination is not possible, haemoglobindetermination may be carried out as analternative, but this is less sensitive.

Volume replacement in DHF

Although there is massive plasma leakage,particularly in shock cases, judicious volumereplacement is mandatory. The required volumeshould be charted on a two or three hourly basisor even more frequently in shock cases. Therate of intravenous fluid replacement should beadjusted throughout the 24-48 hour period ofleakage by serial haematocrit determinations,with frequent assessments of vital signs andurine output, in order to ensure adequatevolume replacement and to avoid over-volumeinfusion. The volume of fluid replacementshould be the minimum that is sufficient tomaintain effective circulation during the periodof leakage. Excessive volume replacement andcontinuation after leakage stops will causemassive pleural effusion, ascites, and pulmonarycongestion/oedema with respiratory distresswhen reabsorption of the extravasated plasmaoccurs in the convalescent stage. In general, thevolume required is maintenance plus 5-8%deficit.

Parenteral fluid therapy can beadministered in outpatient rehydration unitsin mild or moderate cases when vomitingproduces or threatens to produce dehydrationor acidosis or when haemoconcentration ispresent. The fluid administered to correctdehydration from high fever, anorexia andvomiting is calculated according to the degreeof dehydration and electrolyte loss and shouldhave the following composition: 5% glucose

in one-half or one-third physiological salinesolution (PSS). In the case of acidosis, one-fourth of the total fluids should consist of0.167 mol/litre of sodium bicarbonate (i.e.three-quarters PSS plus glucose plus one-quarter sodium bicarbonate).

When there is significant haemo-concentration, i.e. haematocrit elevated 20% ormore of the baseline value (alternatively, thenormal haematocrit value of children in thesame age group in the general population maybe used to estimate the degree ofhaemoconcentration), the fluids used forreplacement therapy should have a compositionsimilar to plasma. The volume and compositionare similar to those used in the treatment ofdiarrhoea with mild to moderate isotonicdehydration (5-8% deficit).

The necessary volume of replacementfluid is equivalent to the amount of fluids andelecrolytes lost: thus, 10ml/kg should beadministered for each 1% of normal bodyweight lost. Maintenance fluid requirements,calculated according to the Halliday andSegar(18) formula (Table 3) should be added tothe replacement fluid. Since the rate ofplasma leakage is not constant (it is more rapidwhen body temperature drops), the volumeand rate of intravenous fluid therapy shouldbe adjusted according to the volume and rateof plasma loss. Plasma loss can be monitoredby changes in the haematocrit, vital signs orvolume of urine output. However, even wherethere is massive plasma loss, judicious fluidreplace-ment is necessary to avoidoverhydration.

The schedule shown in Table 3 isrecommended as a guideline, and has been


24

calculated for moderate dehydration of about6% deficit (plus maintenance). In olderchildren and adults who weigh more than 40kgs, the volume needed for 24 hours shouldbe calculated as twice that required formaintenance.

Patients should be hospitalized andtreated immediately if there are any of thefollowing signs and symptoms of shock:restlessness/lethargy; cold extremities andcircumoral cyanosis; oliguria; rapid and weakpulse; narrowing pulse pressure (20 mm Hgor less) or hypotension, and a sudden rise ofhaematocrit to a high level or continuouslyelevated haematocrit levels despiteadministration of intravenous fluids.

Table 3. Calculations for Maintenanceof Intravenous Fluid Infusion*

Body weight Maintenance volume (ml) (kg) administered over 24 hours

<10 100/kg

10-20 1000 + 50 for each kg inexcess of 10

>20 1500 + 20 for each kg inexcess of 20

* Halliday MA, Segar WE. Maintenance need forwater in parenteral fluid therapy. Pediatrics. 1957,19:823.

Type of fluid:

• Crystalloid:5% dextrose in lactated Ringer’s solution(5% D/RL)5% dextrose in acetated Ringer’s solution(5% D/RA)5% dextrose in half strength normal salinesolution (5% D/1/2/NSS)

5% dextrose in normal saline solution(5% D/NSS)

• Colloidal:Dextran 40Plasma

An example of treatment:

The patient: A two year old child has DHFgrade II, with the following presentation:l High fever for 3 daysl Symptoms worsen on day 4 when

temperature dropsl Physical examination findings: tempera-

ture 37oC, pulse rate 120 per minute, bloodpressure 100/70 mmHg, petechiae and apositive tourniquet test; the liver was tenderand enlarged by 2 cm

l Laboratory findings: platelets 0 to 1 peroil-immersion field, haematocrit 45%(baseline 35%)Administration of intravenous fluid isindicated because the patient has a morethan 20% increase in haematocrit level,and early signs of circulatory disturbanceare indicated by a rapid pulse and agenerally worsening condition.

The following steps should be taken:l Calculate the volume of intravenous fluid

needed for mild isotonic dehydration (5%deficit) based on a 10-kg body-weight.Maintenance fluid: 10 x 100 = 1000ml5% deficit, 50ml/kg10x50 = 500mlTotal volume needed: = 1500ml

l Order 500ml of glucose in Ringer’s lactateor Ringer’s acetate (50 g/litre), or glucosein a half-strength physiological saline(50 g/litre) (if the serum sodium level isnormal):


25

Fluid volume per order should not exceed500 ml, and fluid therapy should not takelonger than 6 hWritten orders should state the type ofsolution and the rate of administration.In this example, the rate is 63 ml per hour,or 21 drops per minute (one ml is equalto 21 drops)

l Follow up vital signs every 1 to 2 h andhaematocrit every 3 to 4 h. Periodicallyrecord urine output and assessment of thepatient’s condition

l Adjust the volume and rate of intravenousfluid according to vital signs, haematocritand urine output as shown in Box 12

(20).

The fluid replacement should be theminimum volume that is sufficient to maintaineffective circulation during the period ofleakage (24-48 hours). Excessive replacementwill cause respiratory distress (from massivepleural effusion and ascites), pulmonarycongestion and oedema.

4.3 Dengue Shock SyndromeShock is a medical emergency. Volumereplacement is the most important treatmentmeasure, and immediate administration ofintravenous fluid to expand plasma volumeis essential. Children may go into and out ofshock during a 48-hour period. Closeobservation with good nursing care 24 hoursa day is imperative (see Box 12).

Immediate replacement of plasma

Start initial intravenous fluid therapy withRinger’s acetate or 5% glucose in normal salinesolution at the rate of 10-20 ml/kg body weight

per hour. Run fluids as rapidly as possible.Positive pressure may be necessary in cases ofprofound shock. If shock persists after initialfluid resuscitation with 10-20 ml/kg body weightper hour, colloidal solution plasma or plasmaexpander (10% Dextran of medium relatedmolecular mass in normal saline solution)should be administered at the rate of 10-20 ml/kg per hour. In most cases, no more than 30ml per kg of body weight of plasma or Dextran40 is needed. In cases of persistent shock afteradequate initial resuscitation with crystalloidand colloidal solutions, despite a decline in thehaematocrit level, significant internal bleedingshould be suspected, and fresh whole-bloodtransfusion is indicated. If the haematocrit levelis still above 40%, a small volume of blood (10ml per kg body weight per hour) isrecommended. When improvement in vitalsigns is apparent, the intravenous infusion rateshould be reduced. Thereafter, it should beadjusted according to the haematocrit levelsand vital signs.

Continued replacement of plasma, basedon frequent micro-haematocritdeterminations

Intravenous administration of fluids should becontinued even when there is a definiteimprovement in the vital signs and thehaematocrit has decreased. The rate of fluidreplacement should be decreased to 10 mlper kilogram per hour, and readjustedthereafter to the rate of plasma loss, whichmay continue for 24 to 48 hours. Thedetermination of central venous pressure mayalso be necessary in the treatment of severecases of shock that are not easily reversible.


26

Box 12. Volume replacement flow chart in dengue hemorrhagic fever

Improvement

Further improvement

HCT

(2) Reduce rate to5 ml/kg/hr

3 ml/kg/hr

(4) Continue at therate as in (2)

(5) Stop IV fluid at24–48 h

HCT, vital signs stableDiuresis

Stable pulse/BPUrine output

Vital sign changesand/or HCT

Pulse PP ≤20 mmHgUrine output

(3) Increase rate to*10 ml/kg/hr

15 ml/kg/hr

Unstable vital signsUrine output

Improvement

HCTHCTand/or distress

(6) Colloid(7) Blood

transfusion

No improvement

Improvement

Follow up HCT/vital signs/urine output

(1) Initial IV fluid5% D/RL 6 ml/kg/hr

RL=Ringer’s lactated; HCT=haematocrit; BP=blood pressure; PP=pulse pressure; *with signs of shock;†establish CVP catheter and urinary catheter

†


27

Intravenous administration of fluidsshould be discontinued when the haematocritdecreases to a stable level, around 40%, andthe patient’s appetite returns. Good urinaryoutput indicates that there is sufficient fluidcirculating. In general, there is no need toadminister fluid therapy for more than 48hours after the termination of shock.Reabsorption of extravasated plasma occurs 2to 3 days thereafter (manifested by a furtherdrop in haematocrit after the intravenousadministration of fluid has been terminated)and may cause hypervolaemia, pulmonaryoedema or heart failure if more fluid is given.It is of the utmost importance that a decreasein the haematocrit in this phase is notinterpreted as a sign of internal haemorrhage.Strong pulse and blood pressure (with widepulse pressure) and diuresis are good vitalsigns during this reabsorption phase. They ruleout the likelihood of gastrointestinalhaemorrhage, which is found primarily in theshock phase.

Other electrolyte and metabolicdisturbances that may require specificcorrection

Hyponatraemia occurs commonly andmetabolic acidosis occurs occasionally inDHF/DSS patients. Electrolyte levels andblood gases should be determined periodicallyin severely ill patients and in those who donot respond as quickly as expected. This willprovide an estimate of the magnitude of theelectrolyte (sodium) deficit and helpdetermine the presence and degree ofacidosis. Acidosis in particular, if unresolved,may lead to disseminated intravascular clottingand to a more complicated course of recovery.

The use of heparin may be indicated in someof these cases, but extreme caution should beexercised when it is administered. In general,early volume replacement and earlycorrection of acidosis with sodiumbicarbonate result in a favourable outcomeand preclude the need for heparin.

Sedatives

In some cases, treatment with sedatives isnecessary to calm an agitated child.Hepatotoxic drugs should be avoided. Chloralhydrate, administered orally or rectally, ishighly recommended at a dosage of 12.5-50mg per kilogram of body weight (but no morethan 1 g) as a single hypnotic dose. Agitation/restlessness that results from poor tissueperfusion often subsides when adequate fluidvolume replacement is given.

Oxygen therapy

Oxygen therapy should be provided for allpatients in shock, but it must be rememberedthat an oxygen mask or tent may lead toincreased patient anxiety.

Blood transfusion

Blood grouping and cross-matching should becarried out as a systematic precaution onevery patient in shock, particularly in caseswith prolonged shock. Blood transfusion isindicated in cases with significanthaemorrhagic manifestations.

It may be difficult to recognize internalhaemorrhage if there is haemoconcentration.A decrease in the haematocrit - e.g. from 0.5


28

(50%) to 0.4 (40%) - without clinicalimprovement, despite the administration ofsufficient fluids, indicates significant internalhaemorrhage. Fresh whole blood is preferableand the volume of blood administered shouldbe only enough to raise the red blood cellconcentration to normal. Fresh frozen plasmaand/or concentrated platelets may beindicated in some cases when disseminatedintravascular coagulation causes massivebleeding.

Disseminated intravascular coagulation iscommon in severe shock, and may play animportant role in the development of massivebleeding and lethal shock. The results ofhaematological tests (e.g. prothrombin time,partial thromboplastin time, and fibrinogendegradation products) should be studied in allpatients with shock to monitor the onset andseverity of disseminated intravascularcoagulation. Results of these tests willdetermine the prognosis.

Essential laboratory tests

In addition to serial haematocrit andplatelet determinations, the following testsare recommended to evaluate the patient’sstatus: studies of the serum electrolytes andblood gases; platelet count, prothrombintime, partial thromboplastin time andthrombin time; and liver function tests -serum aspar ta te aminotrans ferase[(previously known as serum glutamicoxaloacetic transaminase, (SGOT)], serumalanine aminotransferase [ (previous lyknown as serum g lutamic pyruvictransaminase (SGPT)], and serum proteins.

Monitoring and anti-shock therapy

Frequent recording of vital signs andhaematocrit determinations are important inevaluating treatment results. If the patientpresents some indication of secondary shock,vigorous anti-shock therapy should beinstituted promptly. These patients should beunder constant and careful observation untilthere is reasonable assurance that the dangerhas passed. In practice:l The pulse, blood pressure, respirations

and temperature should be recordedevery 15 to 30 minutes or more frequently,until the shock has been overcome.

l Haematocrit levels should be determinedevery two hours during the first six hours,and later every four hours until stable.

l A fluid balance sheet should be kept,recording the type, rate and quantity offluid administered, in order to determinewhether there has been sufficientreplacement and correction of fluids andelectrolytes. The frequency and volumeof urine excreted should also be recorded.

4.4 Criteria for DischargingPatients Hospitalized withDHF/DSS

All of the following six criteria must be metbefore a patient is discharged:l Absence of fever for 24 hours without the

use of antipyretics and a return of appetite.l Visible improvement in clinical picture.l Stable haematocrit.l Three days after recovery from shock.l Platelet count greater than 50,000/mm3.


29

l No respiratory distress from pleuraleffusion/ascites.

4.5 Management of UnusualManifestations/Complications

The most frequently encountered unusualmanifestations are acute hepatic failure andrenal failure (which usually follow prolongedshock) that require specific and appropriatetreatment. Early blood transfusion in cases ofhepatic encephalopathy or Reye’s-likesyndrome has proved to be life saving in anumber of cases, as has haemodialysis in renalfailure cases.

Some DHF patients present unusualmanifestations with signs and symptoms ofCNS involvement, such as convulsion and/orcoma. This has generally been shown to beencephalopathy, not encephalitis, which maybe a result of intracranial haemorrhage orocclusion associated with DIC. In recent years,however, several cases with CNS infectionshave been documented by virus isolationsfrom the CSF or brain(21).

4.6 DHF Special UnitFor the purpose of more effective manage-ment, DHF patients should be hospitalized ina semi-intensive care unit that is a mosquito-free area. Paramedical workers or parents canassist in oral fluid therapy and monitor the IVfluid and the general status of the patient.Experience at the Children’s Hospital,Bangkok, (19) where a great number of DHFcases are seen each year, has shown thatmanagement without using corticosteroids or

any vasopressure drugs, results in a steadydecline in mortality in the case of shock cases.The case fatality rate dropped from about 5%in 1971 to 2% in 1984 and 0.2% in 1990.Studies on the use of corticosteroids in treatingDSS have shown no benefit. The prognosis ofDHF/DSS thus depends on: early diagnosis,early recognition of shock, careful clinicalobservations, and volume replacement guidedby simple laboratory tests(20).

4.7 Role of WHO CollaboratingCentres

Additional information, practice advice andconsultation regarding case management ofDF/DHF/DSS can be obtained from the WHOCollaborating Centres (CC) for CaseManagement of Dengue/DHF/DSS (seeAnnex 1). The WHO Regional Office forSouth-East Asia (SEARO) has supported thetraining of 30 physicians from dengueendemic countries of the Region on clinicalmanagement of dengue/DHF/DSS at this CC.SEARO and the WHO CC will providetechnical support to dengue-training wardsproposed to be established during 1998-99for clinical management of DF/DHF/DSS indengue endemic countries of the Region.Also, it is expected that, through networking,it will be possible not ony to standardize thecase management of DF/DHF/DSS patients,but also to obtain rapid information on theoccurrence of cases which is essential forestablishing early warning systems for dengueoutbreaks and their management (seeBox 13).


30

Box 13Important Considerations in the Clinical Diagnosis and

Management of DHF/DSS

l A child with acute onset of high fever, flushed face without coryza, with petechiaeand/or a positive tourniquet test should suggest a possibility of dengue infection.

l The appearance of hepatomegaly (+ tenderness) increases the possibility of DHF.l The critical stage of the disease is at the time of defervescence. The presence of

thrombocytopenia with concurrent haemoconcentration (rising HCT), which occurbefore the temperature drop and/or onset of shock, are essential to the clinicaldiagnosis of DHF/DSS.

l Moderate marked leukopenia near the end of the febrile period helps in thedifferential diagnosis.

l Antipyretics cannot shorten the duration of fever. Inappropriate use may lead tosevere complications, e.g. severe bleeding, acidosis, hepatic failure.

l Rising haematocrit (by 20% or more) reflects significant plasma loss and a need forIV fluid therapy. Although early IV replacement can prevent shock and modifyseverity, IV fluid therapy before leakage is not recommended.

l DSS is hypovolemic shock due to plasma loss: volume replacement with isotonicsalt solution, plasma or plasma substitute for the period of plasma leakage (24-48 hrs)is life-saving. Dextran 40 is as effective as plasma (maximum dose 30 ml/kg/day),and has some advantages.

l Volume replacement should be carefully monitored according to the rate of plasmaleakage (as reflected by HCT, vital signs, urine output) to avoid fluid overload (therate of leakage is more rapid in the first 6-12 hours)

l Over replacement with more volume and/or for a longer period of time thannecessary will cause pulmonary congestion/oedema, particularly when reabsorptionof extravasated plasma occurs.

l Stagnant acidaemia blood promotes the occurrence/enhances the severity of DIC;acidosis must be corrected. Coagulogram should be evaluated.

l Platelet-rich plasma transfusion as prophylaxis for bleeding in all shock cases is notrecommended.

l There are abnormal haemostatic changes that potentiate bleeding in DHF/DSS.Severe bleeding (may be concealed) often occurs in cases with prolonged shock andfurther perpetuates shock.

l Refractory shock despite adequate volume replacement and a drop in HCT (at anyrate, e.g. from 50% to 40%) indicate significant bleeding and a need for fresh wholeblood transfusion (10ml/kg/dose).

Laboratory DiagnosisL ABORATORY tests essential for

confirmatory diagnosis of dengueinfection include: (a) isolation of the

virus, (b) demonstration of a rising titre ofspecific serum dengue antibodies, and(c) demonstration of a specific viral antigen orRNA in the tissue or serum(21, 22). Isolation ofthe virus is the most definitive approach, butthe techniques presently available require arelatively high level of technical skill andequipment. Serological tests are simpler andmore rapid, but cross-reactions betweenantibodies to dengue and other flavivirusesmay give false positive results. In addition,accurate identification of the infecting dengue

virus serotype is not possible with mostserological methods. New technologiesavailable for the laboratory diagnosis ofdengue infection include immunohisto-chemistry on autopsy tissues and polymerasechain reaction (PCR) to detect viral RNA in thetissue or serum(22).

5.1 Collection of SpecimensAn essential aspect of the laboratory diagnosisof dengue is proper collection, processing,storage and shipment of specimens. The typesof specimens and their storage and shipmentrequirements are presented in Table 4.

31

Table 4. Collecting and processing specimens forlaboratory diagnosis of dengue

Specimen Time of Clot Storage Shipment Type collection retraction

Acute phase 0-5 days after 2-6 hours, 4oC Serum - 70oC Dry iceblood (S1) onsetConvalescent 14-21 days 2-24 hours, Serum – 20oC Frozen orphase blood (S2+S3) after onset ambient ambientTissue As soon as possible 70oC or in Dry ice or

after death formalin ambient

Source: Gubler DJ, and Sather GE. 1988(21)

5

L


32

l Collect a specimen as soon as possibleafter the onset of i l lness, hospitaladmission or attendance at a clinic (this iscalled the acute serum, S1).

l Collect a specimen shortly beforedischarge from the hospital or, in the eventof a fatality, at the time of death(convalescent serum, S2).

l Collect a third specimen, in the eventhospital discharge occurs within 1-2 daysof the subsidence of fever, 7-21 days afterthe acute serum was drawn (lateconvalescent serum, S3).The optimal interval between the acute

(S1) and the convalescent (S2 or S3) serum is10 days. The above recommendations allowfor the collection of at least two serumsamples for comparison, and ideally willprovide for an adequate interval betweensera. Serological diagnoses are predicated onthe identification of changes in antibody levelsover time. Serial (paired) specimens arerequired to confirm or refute a diagnosis ofacute flavivirus or dengue infection.l The type of specimens to be collected,

the way they should be processed for alaboratory diagnosis of dengue, and theinformation required are presented in thischapter. Effective laboratory support forproactive DF/DHF surveillance requiresclose and frequent communicationbetween staff in the laboratory and thosein the epidemiology unit of the ministryof health. It also requires, at a minimum,weekly evaluation of laboratory results,including monitoring the geographiclocation of positive cases, the sero-positivity rate, the virus serotypes isolated,

and the occurrence of severe and fataldisease. This information must becommunicated on a weekly basis to theepidemiology unit for dissemination toother offices in the ministry of health andfor further action. Weekly laboratoryresults are clearly the driving force whichdetermine the response to be taken.

l The above data obtained from a proactivesurveillance system can be used effectivelyif they are disseminated to the propergovernment and community agencies.Thus, an effective communi-cation orreporting system is also a critical componentof the surveillance system. The availabilityof inexpensive yet powerful desktopcomputers that are networked canrevolutionize surveillance reporting since,with the touch of a button, all responsiblepersons/agencies can be informed of thelatest data needed for decision making.

l Samples of suitable request and reportingforms for arbovirus laboratory examinationare provided in Annex II. Blood ispreferably collected in tubes or vials, butfilter paper may be used if this is the onlyoption. Filter-paper samples cannot beused for virus isolation.

Blood collection in tubes or vials

l Aseptically collect 2-10 ml of venous blood.l Use adhesive tape marked with pencil,

indelible ink, or a typewritten self-adhesive label to identify the container.The name of the patient, identificationnumber and date of collection must beindicated on the label.

Laboratory Diagnosis

33

l Use vacuum tubes or vials with screwcaps, if possible. Fix the cap with adhesivetape, wax or other sealing material toprevent leakage during transport.

l Ship specimens to the laboratory on wetice (blood) or dry ice (serum) as soon aspossible. Do not freeze whole blood, ashaemolysis may interfere with serologytest results.

l If there will be more than a 24-hour delaybefore specimens can be submitted to thelaboratory, the serum should be separatedfrom the red blood cells and stored frozen.

Blood collection on filter paper

l With a pencil, write the patient’s initialsor number on two or three filter-paperdiscs or strips of standardized absorbentpaper.*

l Collect sufficient finger-tip blood (orvenous blood in a syringe) on the filterpaper to fully saturate it through to thereverse side. Most standard filter-paperdiscs or strips will absorb 0.1 ml of serum.

l Allow the discs or strips to dry in a placethat is protected from direct sunlight andinsects. Preferably, the blood-soakedpapers should be placed in a stand whichallows aeration of both sides. For unusuallythick papers, a drying chamber may beuseful, e.g. dessicator jar, air-conditionedroom, or warm-air incubator.

l Place the dried strips in plastic bags andstaple them to the laboratory examinationrequest form. Store without refrigeration.

Dried filter-paper discs may be sentthrough the mail.One of the recommended methods for

eluting the blood from filter-paper discs andpreparing it for the HI or IgM and IgG tests isas follows :l Elute the disc at room temperature for 60

minutes or at 4oC overnight, in 1 ml ofkaolin in borate saline (125 g/litre), pH9.0, in a test-tube.

l After elution, keep the tube at roomtemperature for 20 minutes, shakingperiodically.

l Centrifuge for 30 minutes at 600g.l For HI tests using goose erythrocytes,

without removing the kaolin, add 0.05 mlof 50% suspension of goose cells to thetube, shake without disturbing the pellet,and incubate at 37oC for 30 minutes.

l Add 1 ml of borate saline, pH 9.0, to thetube.

l Centrifuge at 600g for 10 minutes anddecant the supernatant.

l This is equivalent to a 1:30 serum dilution.l Each laboratory must standardize the

filter-paper technique against results withvenous blood from a panel of individuals.

5.2 Isolation of Dengue VirusIsolation of most strains of dengue virus fromclinical specimens can be accomplished in amajority of cases provided the sample is takenin the first few days of illness and processedwithout delay. Specimens that may be suitable

____________________________* Whatman No.3 filter-paper discs 12.7 mm (1/2 inch) in diameter are suitable for this purpose, or Nobuto Type 1

blood-sampling paper made by Toyo Roshi Kaisha Ltd., Tokyo, Japan.


34

for virus isolation include acute phase serum,plasma or washed buffy coat from the patient,autopsy tissues from fatal cases, especiallyliver, spleen, lymph nodes and thymus, andmosquitoes collected in nature.

For short periods of storage (up to 48hours), specimens to be used for virus isolationcan be kept at +4 to +8 oC. For longerstorage, the serum should be separated andfrozen at -70oC, and maintained at such sothat thawing does not occur. If isolation fromleucocytes is to be attempted, heparinizedblood samples should be delivered to thelaboratory within a few hours. Wheneverpossible, original material (viraemic serum orinfected mosquito pools) as well as laboratory-passaged materials should be preserved forfuture study.

Tissues and pooled mosquitoes aretriturated or sonicated prior to inoculation.The different methods of inoculation and themethods of confirming the presence ofdengue virus are shown in Table 5. (22)

The choice of methods for isolation andidentification of dengue virus will depend on

local availability of mosquitoes, cell culture, andlaboratory capability. Inoculation of serum orplasma into mosquitoes is the most sensitivemethod of virus isolation, but mosquito cellculture is the most cost-effective method forroutine virologic surveillance. It is essential forhealth workers interested in making adiagnosis by means of virus isolation to makecontact with the appropriate virologylaboratory prior to the collection of specimens.The acquisition, storage and shipment of thesamples can then be organized to have thebest chance of successful isolation.

In order to identify the different denguevirus serotypes, mosquito head squashes andslides of infected cell cultures are examinedby indirect immunoflourescence usingserotype-specific monoclonal antibodies.

5.3 Serological Tests for theDiagnosis of DF/DHF

Five basic serologic tests are routinely usedfor the diagnosis of dengue infection(21,23)

haemagglutination-inhibition (HI), complement

Table 5. Dengue virus isolation methods

Recommended methods Confirmation of dengue virus infection

Inoculation of mosquitoes Presence of antigen in head squashesdemonstrated by immunofluorescence

Inoculation of insect cells or (a) Presence of antigen in cells demonstratedmammalian cultures by immunofluorescence

(b) Cytopathic effect and plaque formation inmammalian cells


35

fixation (CF), neutralization test (NT), IgM-capture enzyme-linked immunosorbent assay(MAC-ELISA), and indirect IgG ELISA.Regardless of the test used, unequivocalserologic confirmation depends upon asignificant (4-fold or greater) rise in specificantibodies between acute-phase andconvalescent-phase serum samples. Theantigen battery for most of these serologic testsshould include all four dengue serotypes,another flavivirus, such as Japaneseencephalitis, a non-flavivirus such aschikungunya, and an uninfected tissue controlantigen, when possible.

Haemagglutination inhibition (HI) test

Of the above tests, HI has been the mostfrequently used for routine serologic diagnosisof dengue infections. It is sensitive, easy toperform, requires only minimal equipment,and is very reliable if properly done. BecauseHI antibodies persist for long periods (up to50 years or longer), the test is ideal forseroepidemiologic studies. The HI test isbased on the fact that the dengue viruses,under controlled conditions of pH andtemperature, can agglutinate goose red bloodcells, and this effect can be inhibited byspecific antibodies. The antigens employedare prepared from infected suckling micebrains by extraction with sucrose and acetoneto remove the lipids, or from infectedmosquito cell cultures that have beenconcentrated or purified. Serum specimensmust be treated to remove non-specificinhibitors and agglutinins.

The HI antibody usually begins to appearat detectable levels (titer of 10) by day five or

six of i l lness, and antibody titers inconvalescent-phase serum specimens aregenerally at or below 1:640 in primaryinfections, although there are exceptions. Bycontrast, there is an immediate anamnesticresponse in secondary and tertiary dengueinfections, and antibody titers increase rapidlyduring the first few days of illness, oftenreaching 1:5,120 to 1:10,240 or more. Thus,a titer of 1:1,280 or greater in an acute-phaseserum is considered a presumptive diagnosisof current dengue infection. High levels of HIantibody may persist for 2-3 months in somepatients, but in most antibody titers willgenerally begin to wane by 30-40 days andfall below the 1:1,280 level.

The major disadvantage of the HI test islack of specificity, which makes the testunreliable for identifying the infecting virusserotype. However, some primary infectionsmay show a relatively monotypic HI responsethat generally correlates with the virusisolated(21).

Complement fixation (CF) test

The CF test is not widely used for routinedengue diagnostic serology. It is more difficultto perform and requires highly-trainedpersonnel. The CF test is based on theprinciple that the complement is consumedduring antigen-antibody reactions. Tworeactions are involved, a test system and anindicator system. Antigens for the CF test areprepared in the same manner as those for theHI test.

CF antibodies generally appear later thanHI antibodies, are more specific in primary


36

infections, and usually persist for shorterperiods, although low-level antibodies maypersist in some persons. Because of the lateappearance of CF antibodies, some patientsmay show a diagnostic rise by CF, but haveonly stable antibody titers by HI. The greaterspecificity of CF test in primary infections isdemonstrated by the monotypic CF responses,whereas HI responses are broadly heterotypic.The CF test is not specific in secondaryinfections. The CF test is useful for patientswith current infections, but is of limited valuefor seroepidemiologic studies where detectionof persistent antibodies is important.

Neutralization test (NT)

The NT is the most specific and sensitiveserologic test for dengue viruses. The mostcommon protocol used in most denguelaboratories is the serum dilution plaquereduction neutralization test (PRNT). It isbased on the fact that dengue viruses producecytopathic effects (CPE) which can beobserved as plaques in susceptible cellcultures. This CPE is neutralized by thepresence of specific antibodies. In general,neutralizing antibodies rise at about the sametime or at a slightly slower rate than HIantibodies, but more quickly than CF, andpersist for at least 50 years or longer. BecauseNT is more sensitive, neutralizing antibodiesmay be detectable in the absence ofdetectable HI antibodies in some persons withpast dengue infection.

The NT can be used to identify theinfecting virus in primary dengue infections,

provided the serum samples are properlytimed. Relatively monotypic responses areobserved in properly timed convalescent-phase serum. As noted above, the HI and CFtests may also give monotypic responses todengue infection that generally agree with NTresults. In those cases where the responses aremonotypic, the interpretation is generallyreliable. In secondary and tertiary infections,it is not possible to reliably determine theinfecting virus serotype by NT. Because of thelong persistence of neutralizing antibodies, thetest may also be used for seroepidemiologicstudies. The major disadvantages are theexpense, time required to perform the test,and technical difficulty. It is therefore notroutinely used in most laboratories.

IgM-capture enzyme-linked immuno-sorbent assay (MAC-ELISA)

MAC-ELISA has become widely used in thepast few years. It is a simple, rapid test thatrequires very little sophisticated equipment.MAC-ELISA is based on detecting thedengue-specific IgM antibodies in the testserum by capturing them out of solutionusing anti-human IgM that was previouslybound to the solid phase (24). I f the IgMantibody from the patient’s serum is anti-dengue antibody, it will bind the dengueantigen that is added in the next step andcan be detected by subsequent addition ofan enzyme labelled anti-dengue antibody,which may be human or monoclonalantibody. An enzyme-substrate is added togive a colour reaction.


37

The anti-dengue IgM antibody developsa litt le faster than IgG, and is usuallydetectable by day five of the illness. However,the rapidity with which IgM develops variesconsiderably among patients. Some patientshave detectable IgM on days two to four afterthe onset of illness, while others may notdevelop IgM for seven to eight days after theonset (22). IgM antibody titers in primaryinfections are significantly higher than insecondary infections, although it is notuncommon to obtain IgM titers of 320 in thelatter cases. In some primary infections,detectable IgM may persist for more than 90days, but in most patients it wanes to anundetectable level by 60 days(21) (Fig.2).

MAC-ELISA is slightly less sensitive thanthe HI test for diagnosing dengue infection.It has the advantage, however, of frequentlyrequiring only a single, properly timed bloodsample. Considering the difficulty in obtainingsecond blood samples and the long delay inobtaining conclusive results from the HI test,this low error rate would be acceptable inmost surveil lance systems. It must beemphasized, however, that because of thepersistence of IgM antibody, MAC-ELISApositive results on single serum samples areonly provisional and do not necessarily meanthat the dengue infection is current. It isreasonably certain, however, that the personhad a dengue infection sometime in theprevious two to three months.

Figure 2. Representation of the temporal appearance of virus, IgM,and IgG antibodies in persons infected with dengue virus.

Shaded areas represent approximate time periods when virus or antibody can be detected using current methods; 1o = primaryinfection; 2o = secondary infection. Gubler DJ 1993, unpublished, prepared for Scientific Publication No.548, PAHO 1994.(25)

Onset ofsymptoms DAYS AFTER ONSET

Viraemia

IgM

IgG(10)

IgG(20)


38

MAC-ELISA has become an invaluabletool for surveillance of DF/DHF/DSS. In areaswhere dengue is not endemic, it can be usedin clinical surveillance for viral illness or forrandom, population-based serosurveys, withthe certainty that any positives detected arerecent infections(21). It is especially useful forhospitalized patients, who are generallyadmitted late in the illness after detectableIgM is already present in the blood.

IgG-ELISA

An indirect IgG-ELISA has been developedthat compares well to the HI test(23). This testcan also be used to differentiate primary andsecondary dengue infections. The test issimple and easy to perform, and is thus usefulfor high-volume testing. The IgG-ELISA is verynon-specific and exhibits the same broadcross-reactivity among flaviviruses as the HItest; it cannot be used to identify the infectingdengue serotype. However, it has a slightlyhigher sensitivity than the HI test. It isexpected that as more data are accumulatedon the IgG ELISA, it will replace the HI test.

Rapid serologic test kits

A number of commercial serologic test kits foranti-dengue IgM and IgG antibodies havebecome available in the past few years, someproducing results within 15 minutes23.Unfortunately, the accuracy of most of thesetests is unknown since they have not yet beenproperly validated. Some of the kits that havebeen independently evaluated at CDC havehad a high rate of false positive resultscompared to standard tests, while others haveagreed closely with standard tests. It isanticipated that these test kits can bereformulated to make them more accurate,thus making global laboratory-basedsurveillance for DF/DHF an obtainable goal inthe near future. It is important to note thatthese kits should not be used in the clinicalsetting to guide management of DF/DHF casesbecause many serum samples taken in the firstfive days after the onset of illness will not havedetectable IgM antibodies. The tests wouldthus give a false negative result. Reliance onsuch tests to guide clinical management could,therefore, result in an increase in case fatalityrates. The relative sensitivity and interpretationof serological tests are given in Annex III.

EpidemiologicalSurveillance

PIDEMIOLOGICAL surveillance ofDF/DHF must cover both disease (case)and entomological (vector) surveillance.

6.1 Case SurveillanceEffective surveillance of DF/DHF infection isessential for monitoring endemic transmissionand for early recognition of impendingepidemics. It depends on close collaborationbetween the epidemiologic, clinical andlaboratory components as well as on anefficient reporting system.

Passive surveillanceEvery dengue endemic country should have asurveillance system and it should be mandatedby law that DF/DHF is a reportable disease.The system should be based on standardizedcase definitions (see Box 14) and formalizedmandated reporting. Although passive systemsare not sensitive and have low specificity sincecases are not laboratory confirmed, they aremost useful in monitoring long-term trends indengue transmission.

The clinical spectrum of illnesses associatedwith dengue infection ranges from non-specific

viral syndrome to severe haemorrhagic diseaseor fatal shock. It may sometimes be difficultto differentiate the illnesses from those causedby other viruses, bacteria and parasites.Therefore, surveillance should be supported bylaboratory diagnosis. However, the reporting ofdengue disease generally has to rely on clinicaldiagnosis combined with simple clinicallaboratory tests and available epidemiologicalinformation.

Passive surveillance should require casereports from every clinic, private physician andhealth centre or hospital that provides medicalattention to the population at risk. However,even when mandated by law, passivesurveillance is insensitive because not all clinicalcases are correctly diagnosed during periods oflow transmission, when the level of suspicionamong medical professionals is low. Moreover,many patients with mild, non-specific viralsyndrome self-medicate at home and do notseek medical treatment. By the time denguecases are detected and reported by physiciansunder a passive surveillance system, substantialtransmission has already occured and may evenhave peaked. In this case, it is often too late tocontrol the epidemic.

39

E

6


40

Box 14Recommended case definition

Dengue Fever

Clinical descriptionAn acute febrile illness of 2-7 days duration with two or more of the following manifestations:headache, retro-orbital pain, myalgia, arthralgia, rash, haemorrhagic manifestations, leucopenia

Laboratory criteria for diagnosisOne or more of the following:

l Isolation of the dengue virus from serum, plasma, leucocytes, or autopsy samplesl Demonstration of a fourfold or greater change in reciprocal IgG or IgM antibody titres to one or

more dengue virus antigens in paired serum samplesl Demonstration of dengue virus antigen in autopsy tissue by immunohistochemistry or

immunofluorescence or in serum samples by ELISAl Detection of viral genomic sequences in autopsy tissue, serum or CSF samples by polymerase

chain reaction (PCR)

Case classificationSuspected: A case compatible with the clinical descriptionProbable: A case compatible with the clinical description with one or more of the following:

– supportive serology (reciprocal haemagglutination-inhibition antibody titre > 1280,comparable IgG ELISA titre or positive IgM antibody test in late acute or convales-cent-phase serum specimen)

– occurrence at same location and time as other confirmed cases of dengue feverConfirmed: A case compatible with the clinical description that is laboratory-confirmed

Criteria For Dengue Haemorrhagic Fever And Dengue Shock Syndrome

Dengue Haemorrhagic FeverA probable or confirmed case of dengue and haemorrhagic tendencies evidenced by one or more of thefollowing:

– positive tourniquet test– petechiae, ecchymoses or purpura– bleeding from mucosa, gastrointestinal tract, injection sites or other sites– haematemesis or melaena

and thrombocytopenia (100,000 cells per mm3 or less)and evidence of plasma leakage due to increased vascular permeability, manifested by one or more ofthe following:

– a rise in average haematocrit for age and sex > 20%– a > 20% drop in haematocrit following volume replacement treatment compared

to baseline– signs of plasma leakage (pleural effusion, ascites, hypoproteinaemia)

Dengue shock syndromeAll the above criteria for DHF plus evidence of circulatory failure manifested by rapid and weak pulse, andnarrow pulse pressure (< 20 mm Hg) or hypotension for age, and cold, clammy skin and restlessness

Source: WHO Recommended Surveillance Standards 1997(14)

Epidemiological Surveillance

41

Active surveillance

The goal of an active dengue surveillancesystem is to allow health authorities to monitordengue transmission in a community and beable to tell, at any point in time, wheretransmission is occurring, which virus serotypesare circulating, and what kind of illness isassociated with the dengue infection(10). Inorder to accomplish this, the system must beactive and have good diagnostic laboratorysupport. Effectively managed, such asurveillance system should be able to providean early warning or predictive capability forepidemic transmission. The rationale is that ifepidemics can be predicted, then they can beprevented.

This type of proactive surveillance systemmust have at least three components that

place the emphasis on the inter or pre-epidemic period, and include a sentinelclinic/physician network, a fever alert systemthat uses community health workers, and asentinel hospital system (Table 6). The sentinelclinic/physician and fever alert components aredesigned to monitor non-specific viralsyndromes in the community. This isespecially important for dengue virusesbecause they are frequently maintained intropical urban centres in a silent transmissioncycle, often presenting as non-specific viralsyndromes. The sentinel clinic/physician andfever alert systems are also very useful formonitoring other common infectious diseases,such as influenza, measles, malaria, typhoid,leptospirosis, and others that present in theacute phase as non-specific febrile illnesses.

Table 6. Components of Laboratory-Based, Proactive Surveillance for Dengue andDengue Haemorrhagic Fever during Interepidemic Periodsa

Type of Samplesb ApproachSurveillance

a During an epidemic, after the virus serotype(s) is known, the case definition should be more specific andsurveillance focused on severe disease.

b All samples are processed weekly for virus isolation and/or for dengue specific IgM antibodies.

SentinelHospital

Blood and tissue samples takenduring hospitalization and/or atdeath

All haemorrhagic disease and all viralsyndromes with fatal outcome areinvestigated immediately

Fever Alert Blood samples from representa-tive cases of febrile illness

Increased febrile illness in the commu-nity is investigated immediately

SentinelClinic/Physician

Blood from representative cases ofviral syndrome, taken from 3 to 15days after the onset of symptoms

Representative samples taken yearround and processed weekly forvirus isolation and for IgM antibodies


42

In contrast to the sentinel clinic/physiciancomponent, which requires sentinel sites tomonitor routine viral syndromes, the feveralert system relies on community health,sanitation and other workers to be alert to anyincrease in febrile activity in their communityand to report this to the central epidemiologyunit of the health department. Investigation bythe latter should be immediate, but flexible.It may involve telephone follow up or activeinvestigation by an epidemiologist who visitsthe area to take samples.

The sentinel hospital component shouldbe designed to monitor severe disease.Hospitals used as sentinel sites should includeall of those that admit patients for severeinfectious diseases in the community. Thisnetwork should also include the infectiousdisease physicians who usually consult on suchcases. The system can target any type ofsevere disease, but for dengue it shouldinclude all patients with any haemorrhagicmanifestation, an admission diagnosis of viralencephalitis, aseptic meningitis andmeningococcal shock, and/or a fatal outcomefollowing a viral prodrome(10).

All three surveillance components requirea good public health laboratory to providediagnostic support in virology, bacteriology andparasitology. The laboratory does not need tobe able to test for all agents, but should knowwhere to refer specimens for testing, i.e. toWHO collaborating centres for reference andresearch.

An active surveillance system is designedto monitor disease activity during the inter-epidemic period, prior to increased trans-mission. Individually, the three components

are not sensitive enough to provide effectiveearly warning, but used collectively, they canoften accurately predict epidemic activity.Table 6 outlines the active surveillance systemfor DF/DHF, giving the types of specimens andapproaches required. It must be emphasizedthat once epidemic transmission has begun,the active surveillance system is refocused onsevere disease rather than on viral syndromes.Surveillance systems should be designed andadapted to the areas where they will beinitiated.

6.2 Vector SurveillanceSurveillance for Ae. aegypti is important indetermining the distribution, populationdensity, major larval habitats, spatial andtemporal risk factors related to denguetransmission, and levels of insecticide suscepti-bility or resistance(26), in order to prioritize areasand seasons for vector control. These data willenable the selection and use of the mostappropriate vector control tools, and can beused to monitor their effectiveness. There areseveral methods available for the detection andmonitoring of larval and adult populations. Theselection of appropriate sampling methodsdepends on surveillance objectives, levels ofinfestation, and availability of resources.

Larval surveys

For practical reasons, the most common surveymethodologies employ larval samplingprocedures rather than egg or adultcollections. The basic sampling unit is thehouse or premise, which is systematicallysearched for water-holding containers.


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Containers are examined for the presence ofmosquito larvae and pupae. Depending on theobjectives of the survey, the search may beterminated as soon as Aedes larvae are found,or it may be continued until all containers havebeen examined. The collection of specimensfor laboratory examination is necessary toconfirm the species present. Three indices thatare commonly used to monitor Ae. aegyptiinfestation levels(25, 26) are presented in Box 15.

The house index has been most widelyused for monitoring infestation levels, but itdoes not take into account the number ofpositive containers nor the productivity of thosecontainers. Similarly, the container index only

provides information on the proportion ofwater-holding containers that are positive. TheBreteau index establishes a relationshipbetween positive containers and houses, andis considered to be the most informative, butagain there is no reflection of containerproductivity. Nevertheless, in the course ofgathering basic information for calculating theBreteau index, it is possible and desirable toobtain a profile of the larval habitatcharacteristics by simultaneously recording therelative abundance of the various containertypes, either as potential or actual sites ofmosquito production (e.g. number of positivedrums per 100 houses, number of positivetyres per 100 houses, etc.). These data areparticularly relevant for focusing control effortson the management or elimination of themost common habitats and for the orientationof educational messages for community-based initiatives.

The rate of contribution of newly-emerged adults to the adult mosquitopopulation from different container types canvary widely. The estimates of relative adultproduction may be based on pupal counts(26)

(i.e. counting all pupae found in eachcontainer). The corresponding index is thePupal index (Box 16).

Box 15Indices used to assess the levels of

Ae. aegypti infestations

House index (HI): percentage of housesinfested with larvae and/or pupae.

Number of houses infestedHI = ———————————— x 100

Number of houses inspected

Container index(CI): percentage ofwater-holding containers infested withlarvae or pupae.

Number of positive containersCI = ————————————— x 100

Number of containers inspected

Breteau index (BI): number of positivecontainers per 100 houses inspected.

Number of positive containersBI = ————————————— x 100


Box 16Pupal index: number of pupae

per 100 houses

Number of pupaePI = —————————————X 100



44

In order to compare the relative importanceof larval habitats, the pupal index can be brokendown to “useful”, “non-essential” and “natural”containers, or by specific habitat types, such astyres, flower vases, drums, clay pots, etc. Giventhe practical difficulties and labour-intensiveefforts entailed in obtaining pupal counts,especially from large containers, this methoddoes not need to be used in every survey, butmay be reserved for special studies or used oncein each locality during the wet season and onceduring the dry season, to determine the mostproductive container types. The pupal index hasbeen most frequently used for operationalresearch purposes.

Adult surveys

Adult vector sampling procedures can providevaluable data for specific studies, such asseasonal population trends, transmissiondynamics, transmission risk, and evaluation ofadulticiding interventions. However, resultsmay be less reproducible than those obtainedfrom sampling of immature stages. Thecollection methods also tend to be labour-intensive and heavily dependent on thecollector’s proficiency and skill.

Landing/biting collections

Landing/biting collections on humans are asensitive means of detecting low-levelinfestations, but are very labour-intensive. Bothmale and female Ae. aegypti are attracted tohumans. Because adult males have lowdispersal rates, their presence can be a reliableindicator of close proximity to hidden larvalhabitats. The rates of capture, typically using

hand nets or aspirators as mosquitoes approachor land on the collector, are usually expressedin terms of landing/biting counts per man hour.

As there is no prophylaxis for dengue orother viruses transmitted by Aedes mosquitoes,it is highly desirable, for ethical reasons, thatadult captures of Aedes vectors should bebased on “landing collections” only. Instructionmust be clearly given to all field staff involvedin entomological work in DF/DHF controlprogrammes that every effort should be madeto avoid being bitten.

Resting collections

During periods of inactivity, adult mosquitoestypically rest indoors, especially in bedrooms,and mostly in dark places, such as clothes closetsand other sheltered sites. Resting collectionsrequire systematic searching of these sites foradult mosquitoes with the aid of a flashlight. Alabour-intensive method is to capture the adultsusing mouth or battery-powered aspirators andhand-held nets with the aid of flashlights.Recently, a much more productive, standardizedand less labour-intensive method using battery-operated back-pack aspirators has beendeveloped(27). Following a standardized, timedcollection routine in selected rooms of eachhouse, densities are recorded as the number ofadults per house (females, males or both) or thenumber of adults per human-hour of effort.When the mosquito population density is low,the percentage of houses positive for adults issometimes used.

Oviposition traps

“Ovitraps” are devices used to detect thepresence of Ae. aegypti and Ae. albopictus


45

where the population density is low and larvalsurveys are largely unproductive (e.g. whenthe Breteau index is less than 5), as well asunder normal conditions. They are particularlyuseful for the early detection of newinfestations in areas from which themosquitoes have been previously eliminated.For this reason, they are used for surveillanceat international ports of entry, particularlyairports, which comply with internationalsanitary regulations and which should bemaintained free of vector breeding. An ovitrapenhanced with hay infusion has been shownto be a very reproducible and efficientmethod for Ae. aegypti surveillance in urbanareas and has also been shown to be usefulto evaluate control programmes, such as theimpact of adulticidal space spraying on adultfemale populations(28).

The standard ovitrap is a wide-mouthed,pint-sized glass jar, painted black on theoutside. It is equipped with a hardboard orwooden paddle clipped vertically to the insidewith its rough side facing inwards. The jar ispartially filled with water and is placedappropriately in a suspected habitat, generallyin or around homes in the environment. The“enhanced CDC ovitrap” has yielded eighttimes more Ae. aegypti eggs than the originalversion. In this method, double ovitraps areplaced. One jar contains an olfactory attractantmade from a “standardized” seven-day-oldinfusion, while the other contains a 10 percentdilution of the same infusion. Ovitraps areusually serviced on a weekly basis, but in thecase of enhanced ovitraps, they are servicedevery 24 hours. The paddles are examinedunder a dissecting microscope for the presence

of Ae. aegypti eggs, which are then countedand stored. In areas where both Ae. aegyptiand Ae. albopictus occur, eggs should behatched and larvae or adults identified, sincethe eggs of those species cannot be reliablydistinguished from each other. The percentageof positive ovitraps provides a simple index ofinfestation levels, or if the eggs are counted,it can provide an estimate of the adult femalepopulation.

Tyre section larvitraps

Tyre section larvitraps of various designs havealso been used for monitoring oviposition activity,the simplest being a water-filled radial sectionof an automobile tyre. A prerequisite for anydesign is that it either facilitates visual inspectionof the water in situ or allows the ready transferof the contents to another container forexamination. Tyre larvitraps differ from ovitrapsin that water level fluctuations brought about byrainfall induce hatching of eggs, hence thepresence of larvae is noted rather than thepaddles on which eggs have been deposited.The placement and use of this method isdiscussed in more details in reference 26.

Epidemiological interpretations ofvector surveillance

Adult surveillance

The epidemiology of dengue infection may becomplicated because Ae. aegypti may proberepeatedly on one or more persons during asingle blood meal. The correlation of differententomological indices in terms of actual diseasetransmission is difficult. The interpretation of


46

the epidemiology of dengue transmission musttake into account inter-urban populationmovement, focality of Aedes populationswithin the urban area, and fluctuations in adultpopulation densities, which influencetransmission intensity. More attention shouldbe given to understanding the relationshipsamong adult vector densities, densities of thehuman population in different areas of the city,and the transmission of dengue viruses.

Larval surveillance

The commonly-used larval indices (house,container and Breteau) are useful fordetermining general distribution, seasonalchanges and principal larval habitats, as wellas for evaluating environmental sanitationprogrammes. However, they generally have norelevance to the dynamics of diseasetransmission. The precise levels of vectorinfestation that constitute a “risk” level fordengue transmission are influenced by manyfactors, including mosquito longevity andimmunological status of the human population.There are examples (e.g. Singapore) wheredengue transmission occurred even when theHouse Index was less than 2%. Therefore, thelimitations of these indices must be recognizedand studied more carefully to determine howthey correlate with adult female populationdensities, and how all indices correlate withthe disease-transmission risk. The developmentof alternative, practical and more sensitiveentomological surveillance methodologies is anurgent need. The level and type of vectorsurveillance selected by each country orcontrol programme should be determined byoperational research activities conducted at thelocal level.

Sampling strategiesThe sample size for routine larval surveysshould be calculated using statistical methodsbased on the expected level of infestation andthe desired level of confidence in the results.Annex IV gives tables and examples fordetermining the number of houses to beinspected. Several approaches can be used.

Systematic samplingEvery nth house is examined throughout acommunity or along linear transects throughthe community. For example, if a sample of5% of the houses is to be inspected, every20th house would be inspected. This is apractical option for rapid assessment of vectorpopulation levels, especially in areas wherethere is no house numbering system.

Simple random samplingThe houses to be examined are obtained froma table of random numbers (found in statisticaltext books or from a calculator or computer-generated list). This is a more laboriousprocess, as detailed house maps or lists ofstreet addresses are a prerequisite foridentifying the selected houses.

Stratified random samplingThis approach minimizes the problem of under-and over-representation by subdividing thelocalities into sectors or “strata”. Strata areusually based on identified risk factors, suchas areas without piped water supply, areas notserved by sanitation services, and densely-populated areas. A simple random sample istaken from each stratum, with the number ofhouses inspected being in proportion to thenumber of houses in that sector.


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Frequency of sampling

Control programmes using integrated strategiesdo not require sampling at frequent intervalsto assess the impact of the applied controlmeasures. This is especially true where theeffect of the alternative strategies outlastsresidual insecticides (for example, larvivorousfish in large potable water storage containers,source reduction or mosquito-proofing ofcontainers) or when larval indices are high (HIgreater than 10%). On the other hand,feedback on at least a monthly basis may bedesirable to monitor and guide communityactivities and to identify the issues that needmore scrutiny, especially when the HI is 10%or lower. For specific research studies, it maybe necessary to sample on a weekly, daily oreven hourly basis (e.g. to determine thediurnal pattern of biting activity).

Insecticide susceptibility testing

Information on the susceptibility of Ae. aegyptito insecticides for the planning and evaluationof control is of fundamental importance. Thestatus of resistance in a population must becarefully monitored to ensure that timely andappropriate decisions are made to use alternativeinsecticides or to change control strategies.

Standard WHO susceptibility testprocedures and kits are available to determinethe susceptibility or level of resistance ofmosquito larvae and adults to insecticides(WHO, 1981) (29). Test kits can be ordered andpurchased through WHO Representatives(WRs) at country level and WHO regionaloffices. Biochemical and immunologictechniques for testing individual mosquitoes

have also been developed but are not yetavailable for routine field use.

Additional information forentomological surveillance

In addition to the evaluation of aspects directlypertaining to vector density and distribution,community-oriented, integrated pestmanagement strategies require that otherparameters be measured or periodicallymonitored. These include the distribution anddensity of the human population, settlementcharacteristics, and conditions of land tenure,housing styles and education. The monitoringof these parameters is relevant and ofimportance to planning purposes and forassessing the dengue risk. The knowledge ofchanges over time in the distribution of watersupply services, their quality and reliability, aswell as in domestic water storage and solidwaste disposal practices is also particularlyrelevant. Meteorological data are alsoimportant. Such information aids in planningtargeted source reduction and managementactivities, as well as in organizing epidemicintervention measures.

Some of these data sets are generated bythe health sector, but other sources of datamay be necessary. In most cases, annual oreven less frequent updates will suffice forprogramme management purposes. In thecase of meteorologic data, especially rainfallpatterns, humidity and temperature, a morefrequent weekly analysis is warranted if it isto be of predictive value in determining theseasonal trends and short-term fluctuations ofvector populations.

Vector Distribution andBioecology

I N the South-East Asia Region, Aedesaegypti is the principal epidemic vectorof dengue viruses. Aedes albopictus has

been recognized as a secondary vector, whichalso is important in the maintenance of theviruses. The distribution and biology of thesetwo species are described below.

7.1 Aedes aegypti

Taxonomic status

Aedes aegypti exhibits a continuous spectrumof scale patterns across its range of distributionfrom a very pale form to a dark form, withassociated behavioural differences(30). It isessential to understand the bionomics of thelocal mosquito population as a basis for itscontrol.

Geographical distribution in South-East Asia

Distribution

Ae. aegypti is widespread in tropical andsubtropical areas of South-East Asia, and iscommon in most urban areas. The rural spread

of Ae. aegypti is a relatively recent occurrenceassociated with the development of rural watersupply schemes and improved transportsystems (see Figure 3).

In semi-arid areas, i.e. India, Ae. aegyptiis an urban vector and populations typicallyfluctuate with rainfall and water storagehabits(31). In other countries of South-East Asia,where the annual rainfall is greater than 200cm, Ae. aegypti populations are more stableand are established in urban, semi-urban andrural areas. Because of traditional water storagepractices in Indonesia, Myanmar and Thailand,their densities are higher in semi-urban areasthan in urban areas.

Urbanization tends to increase thenumber of habitats suitable for Ae. aegypti. Insome cities where vegetation is abundant,both Ae. aegypti and Ae. albopictus occurtogether, but generally Ae. aegypti is thedominant species, depending on theavailability and type of larval habitat and theextent of urbanization. In Singapore, forexample, the premise index was highest forAe. aegypti in slum houses, shop houses andmultistoried flats. Ae. albopictus, on the otherhand, did not seem to be related to the

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prevailing housing types, but was more commonin areas with open spaces and vegetation.

Altitude

Altitude is an important factor in limiting thedistribution of Ae. aegypti. In India, Ae. aegyptiranges from sea level to 1000 metres above sealevel. Lower elevations (less than 500 meters)have moderate to heavy mosquito popula-tions(32) while mountainous areas (greater than500 meters) have low populations. In countriesof South-East Asia, 1000 to 1500 metres appearsto be the limit for Ae. aegypti distribution. Inother regions of the world, it is found at evenhigher altitudes, i.e. up to 2200 metres(33) inColumbia.

Ecology and bionomics

Eggs

Eggs are deposited singly on damp surfaces justabove the water line. Most female Ae. aegyptiwill lay eggs in several oviposition sites duringa single gonotrophic cycle. Embryonicdevelopment is usually completed in 48 hoursin a warm and humid environment. Onceembryonation development is complete, theeggs can withstand long periods of desiccation(more than a year). Eggs hatch once thecontainers are flooded, but not all eggs hatchat the same time. The capacity of eggs towithstand desiccation facilitates the survival ofthe species during adverse climatic conditions.

Figure 3. World distribution map of Dengue and Aedes aegypti in 1998

Areas infested with Aedes aegyptiAreas with Aedes aegypti and dengue epidemic activity

Source: Gubler DJ. 1998(10)

Vector Distribution and Bioecology

51

Larvae and pupae

The larvae pass through four developmentalstages. The duration of larval developmentdepends on temperature, availability of food,and larval density in the receptacle. Underoptimal conditions, the time taken fromhatching to adult emergence can be as shortas seven days, including two days in the pupalstage. At low temperatures, however, it maytake several weeks for adults to emerge.

Throughout most of South-East Asia,Ae.aegypti oviposits almost entirely indomestic, man-made water receptacles. Theseinclude a multitude of receptacles found inand around urban environments (households,construction sites and factories), such as water-storage jars, plates on which flower pots stand,flower vases, cement baths, foot baths,wooden and metal barrels, metal cisterns,tyres, bottles, tin cans, polystyrene containers,plastic cups, discarded wet-cell batteries, glasscontainers associated with “spirit houses”(shrines), drain pipes and ant-traps in whichthe legs of cupboards and tables often stand.Natural larval habitats are more rare, butinclude tree-holes, leaf axils and coconutshells. In hot and dry regions, overhead tanks,groundwater storage tanks and septic tanksmay be primary habitats. In areas where watersupplies are irregular, inhabitants store waterfor household use, thereby increasing thenumber of available larval habitats.

Adults

Soon after emergence, the adult mosquitoesmate and the inseminated female may take ablood meal within 24-36 hours. Blood is thesource of protein essential for the maturationof eggs.

Feeding behaviour

Ae. aegypti is highly anthropophilic, althoughit may feed on other available warm bloodedanimals. Being a diurnal species, females havetwo periods of biting activity, one in themorning for several hours after daybreak andthe other in the afternoon for several hoursbefore dark(34,35,36). The actual peaks of bitingactivity may vary with location and season. Inthe case of interrupted feeding, Ae. aegyptimay feed on more than one person. Thisbehaviour greatly increases the epidemictransmission efficiency. Thus, it is notuncommon to see several members of thesame household with an onset of illnessoccurring within 24 hours, suggesting that theywere infected by the same infectivemosquito(10). Ae. aegypti generally does not biteat night, but it will feed at night in lightedrooms(35).

Resting behaviour

Ae. aegypti prefers to rest in dark, humid,secluded places inside houses or buildings,including bedrooms, closets, bathrooms andkitchens. Less often it can be found outdoorsin vegetation or other protected sites. Thepreferred indoor resting surfaces are theundersides of furniture, hanging objects suchas clothes and curtains, and on walls.

Flight range

The dispersal of adult female Aedes aegypti isinfluenced by a number of factors includingavailability of oviposition sites and blood meals,but appears to be often limited to within 100meters of the site of emergence. However,


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recent studies in Puerto Rico indicate that theymay disperse more than 400 meters primarilyin search of oviposition sites. (37) Passivetransportation can occur via eggs and larvae incontainers.

Longevity

Aedes aegypti has an average adult survival ofonly eight days(36). During the rainy season,when survival is longer, the risk of virustransmission is greater. More research isrequired on the natural survival of Ae. aegyptiunder various environmental conditions.

Virus transmission

A vector mosquito may become infectedwhen it feeds on a viraemic human host. Inthe case of DF/DHF, viraemia in the humanhost may occur 1-2 days before the onset offever and lasts for about five days after theonset of fever(38). After an intrinsic incubationperiod of 10-12 days, the virus grows throughthe midgut to infect other tissues in themosquito, including the salivary glands. If itbites other susceptible persons after thesalivary glands become infected, it transmitsdengue virus to those persons by injecting thesalivary fluid.

7.2 Aedes albopictusAedes albopictus belongs to the same subgenus(Stegomyia) as Ae. aegypti. This species iswidely distributed in Asia from tropical to

temperate countries. During the past twodecades, the species has extended its rangeto North and South America, the Caribbean,Africa, Southern Europe and some Pacificislands (39).

Ae. albopictus is primarily a forest speciesthat has become adapted to rural, suburbanand urban human environments. It ovipositsand develops in tree holes, bamboo stumpsand leaf axils in forest habitats; and in theseplus artificial containers in urban settings. It isan indiscriminate blood feeder and morezoophagic than Ae. aegypti. Its flight rangemay be up to 500 metres. Unlike Ae. aegypti,some strains are cold adapted in Northern Asiaand America, with eggs that spend the winterin diapause.

In some areas of Asia and in theSeychelles, Ae. albopictus has beenoccasionally incriminated as the vector ofepidemic DF/DHF, though it is much lessimportant than Ae. aegypti. In the laboratory,both species can transmit dengue virusvertically from a female through the eggs toher progeny, although Ae. albopictus does somore readily(9).

7.3 Vector IdentificationPictorial keys to Aedes (Stegomyia) mosquitoesbreeding in domestic containers are given inAnnex V (40). The keys include Culexquinquefasciatus which may be found in thesame habitats.

Prevention and ControlMeasures

N O VACCINE is available yet for theprevention of dengue infection andthere are no specific drugs for its

treatment. Hence DF/DHF control is primarilydependent on the control of Ae. aegypti.

Dengue control programmes in theRegion have in general not been verysuccessful, primarily because they have reliedalmost exclusively on space spraying ofinsecticides for adult mosquito control.However, space spraying requires specificoperations which were often not adhered to,and most countries found it cost prohibitive.

In order to achieve sustainability of asuccessful DF/DHF vector control programme,it is essential to focus on larval sourcereduction and to have complete cooperationwith non-health sectors, such as nongovern-mental organizations, civic organizations andcommunity groups, to ensure communityunderstanding and involvement in implemen-tation. There is, therefore, a need to adopt anintegrated approach to mosquito control byincluding all appropriate methods (environ-mental, biological and chemical) which are

safe, cost-effective and environmentallyacceptable. A successful, sustainable Ae.aegypti control programme must involve apartnership between government controlagencies and the community. The approachesdescribed below are considered necessary toachieve long-term, sustainable control of Ae.aegypti.

8.1 Environmental ManagementEnvironmental management involves anychange that prevents or minimizes vectorbreeding and hence reduces human-vectorcontact. The control of Ae. aegypti in Cuba andPanama in the early part of this century wasbased mainly on environmental management.Such measures remain applicable whereverdengue is endemic. The World HealthOrganization(41) (1982) has defined three kindsof environmental management (Box 17).

Environmental methods to control Ae.aegypti and Ae. albopictus and to reduceman-vector contact are source reduction, solidwaste management, modification of man-

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made breeding sites, and improved housedesign. The major environmentalmanagement methods used for the control ofthe immature stages of dengue vectors aresummarized in Box 18.

Environmental modification

Improved water supply

Whenever piped water supply is inadequateand available only at restricted hours or at lowpressure, the storage of water in varied typesof containers is encouraged, thus leading toincreased Aedes breeding. The majority ofsuch containers are large and heavy (e.gstorage jars) and can neither be easilydisposed of nor cleaned. In rural areas,unpolluted, disused wells become breedinggrounds for Ae. aegypti. It is essential thatpotable water supplies be delivered insufficient quantity, quality and consistency toreduce the necessity and use of water storagecontainers that serve as the most productivelarval habitats.

Mosquito-proofing of overhead tanks/cisterns or underground reservoirs

Where Ae. aegypti larval habitats includeoverhead tanks/cisterns and masonarychambers of piped waterlines, these structuresshould be mosquito-proofed(42). A suggesteddesign is illustrated in Annex VI. Similarly,mosquito-proofing of domestic wells andundergroundwater storage tanks should beundertaken. Masonary chambers of sluicevalves and water meters are required to beprovided with soak pits as part of preventivemaintenance (Annex VI).

Environmental manipulation

Draining of water supply installations

Water collection/leakages in masonrychambers, distribution pipes, valves, sluicevalves, surface boxes for fire hydrants, watermeters, etc. collect water and serve asimportant Ae.aegypti larval habitats in theabsence of preventive maintenance.

Domestic storage

The major sources of Ae. aegypti breeding inmost urban areas of South-East Asia arecontainers storing water for household useincluding clay, ceramic and cement water jarsof 200 litre size, 210 litre (50 gallon) metaldrums, and smaller containers storing freshwater or rain water. Water storage containersshould be covered with tight-fitting lids or

Box 17Environmental Management

Methods

l Environmental modification: long-lasting physical transformation ofvector habitats.

l Environmental manipulation:temporary changes to vectorhabitats that involve themanagement of “essential” and“nonessential” containers; andmanagement or removal of“natural” breeding sites.

l Changes to human habitation orbehaviour: efforts to reduce man-vector-virus contact.

Prevention and Control Measures

55

Box 18Environmental measures for the control of

Aedes aegypti production sites

Store Modify Fill Collect PunctureProduction site Clean Cover under design (sand/ recycle/ or drain

roof soil) dispose

EssentialWater storage tank/cistern + + +

Drum (40-55 gal) + + +

Flower vase with water + +

Potted plants with saucers +

Ornamental pool/fountain +

Roof gutter/sun shades +

Animal water container +

Ant trap +

Non-essentialUsed tyres + + + +

Discarded large appliances +

Discarded buckets + +

Tin cans + +

NaturalTreeholes +

Rock holes +


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screens, care being taken to replace themafter water is used. An example of the efficacyof this approach has recently beendemonstrated in Thailand(43).

Flower pots/vases and ant traps

Flower pots, flower vases and ant traps arecommon sources of Ae. aegypti breeding. Theyshould be punctured to produce a drain hole.Alternatively, live flowers can be placed in amixture of sand and water. Flowers should beremoved and discarded weekly and vasesscrubbed and cleaned before reuse. Brassflower pots, which make poor larval habitats,can be used in cemeteries in place of traditionalglass containers. Ant traps to protect foodstorage cabinets can be treated with commonsalt or oil.

Aedes breeding in incidental watercollections

Desert (evaporation) water coolers,condensation collection pans underrefrigerators, and air conditioners should beregularly inspected, drained and cleaned.Desert water coolers generally employed inarid/semi-arid regions(44) of South-East Asia tocool houses during summer contain twomanufacturing defects. These are as follows:(1) The exit pipe at the bottom of the water-holding tray is generally fixed a fewcentimetres above the bottom. This exit pipeshould be fitted at such a level that whileemptying the tray, all the water should getdrained off without any retention at thebottom.(2) Desert coolers are normally fitted towindows with the exit pipe located on the

exterior portion of the tray. These sites areusually difficult to access, and, therefore, thereis a need to change the design so that boththe filling and emptying of the water-holdingtrays can be manipulated from the room, thuseliminating the need of climbing to approachthe exit pipe at the exterior of the building.

It is recommended that each countryshould develop regulatory mechanisms toensure the design specifications as outlinedabove for manufacturing desert coolers.

Building exteriors

The design of buildings is important to preventAedes breeding. Drainage pipes of rooftopssunshades/porticos often get blocked andbecome breeding sites for Aedes mosquitoes.There is a need for periodic inspection ofbuildings during the rainy season to locatepotential breeding sites.

Mandatory water storage for firefighting

Fire prevention regulations may requiremandatory water storage. Such storage tanksneed to be kept mosquito-proofed. In somemunicipalities in India(45), timber merchantsare required to maintain two metal drums (50gallons) full of water for fire fighting. Thesedrums should be kept covered with tight lids.Also, metal drums used for water storage atconstruction sites should be mosquito-proofed.

Solid waste disposal

Solid wastes, namely tins, bottles, buckets orany other waste material scattered around


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houses, should be removed and buried inland fills. Scrap material in factories andwarehouses should be stored appropriatelyuntil disposal. Household and garden utensils(buckets, bowls and watering devices) shouldbe turned upside down to prevent theaccumulation of rain water. Similarly, canoesand small boats should be emptied of waterand turned upside down when not in use. Plantwaste (coconut shells, cocoa husks) should bedisposed of properly and without delay.

Tyre management

Used automobile tyres are of major importanceas breeding sites for urban Aedes, and aretherefore a significant public health problem.Imported used tyres are believed responsible forthe introduction of Ae. albopictus into theUnited States, Europe and Africa(46). Tyre depotsshould always be kept under cover to preventthe collection of rain water.

New technologies for tyre recycling anddisposal are continually coming into use, butmost of them have proved to be of limitedapplication or cost-effectiveness. Used tyrescan be filled with earth or concrete and usedfor planters or traffic/crash barriers. They mayalso be used as soil erosion barriers, or usedto create artificial reefs and reduce beacherosion by wave action. Tyres can also berecycled for sandals, floormats, industrialwashers, gaskets, buckets, garbage pails andcarpet backing, while truck tyres have beenmade into durable, low-cost refuse containers.

Filling of cavities of fences

Fences and fence posts made from hollowtrees such as bamboo should be cut down to

the node, and concrete blocks should be filledwith packed sand, crushed glass, or concreteto eliminate potential Aedes larval habitats.

Glass bottles and cans

Glass bottles, cans and other small containersshould be buried in land fills or crushed andrecycled for industrial use.

8.2 Personal Protection

Protective clothing

Clothing reduces the risk of mosquito bitingif the cloth is sufficiently thick or loosely fitting.Long sleeves and trousers with stockings mayprotect the arms and legs, the preferred sitesfor mosquito bites. Schoolchildren shouldadhere to these practices whenever possible.Impregnating clothing with chemicals such aspermethrin can be especially effective inpreventing mosquito bites.

Mats, coils and aerosols

Household insecticidal products, namelymosquito coils, pyrethrum space spray andaerosols have been used extensively forpersonal protection against mosquitoes.Electric vaporizer mats and liquid vaporizersare more recent additions which are marketedin practically all urban areas.

Repellents

Repellents are a common means of personalprotection against mosquitoes and other bitinginsects. These are broadly classified into twocategories, natural repellents and chemical


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repellents. Essential oils from plant extracts arethe main natural repellent ingredients, i.e.citronella oil, lemongrass oil and neem oil.Chemical repellents such as DEET (N, N-Diethyl-m-Toluamide) can provide protectionagainst Ae. albopictus, Ae. aegypti andanopheline species for several hours.Permethrin is an effective repellant whenimpregnated in cloth.

Insecticide-treated mosquito nets andcurtains

Insecticide-treated mosquito nets (ITMN) havelimited utility in dengue control programmes,since the vector species bites during the day.However, treated nets can be effectivelyutilized to protect infants and night workerswho sleep by day. They can also be effectivefor people who generally have an afternoonsleep. For details of insecticide treatment ofmosquito nets and curtains, see Annex VII.

“Olyset net”, a wide mesh net wovenfrom polyethylene thread containing 2%permethrin, is yet another improvement inITMN technology. This net has two advantagesover traditional nets in that the wide meshpermits better ventilation and light, and thetreated thread enables a slow release ofpermethrin to the fibre surface, ensuring along residual effect (over a year). In studiescarried out in Malaysia, four washings withsoap and water did not diminish the efficacyand the mortality of Ae. aegypti was 86.7%(47).For control of DF/DHF in Vietnam, Olyset netcurtains were hung on the inside againstdoors/windows; Ae. aegypti was adverselyaffected and dengue virus transmission was

interrupted(48). Further studies on impregnatedfabrics appear warranted.

8.3 Biological ControlThe application of biological control agentswhich are directed against the larval stages ofdengue vectors in South-East Asia has beensomewhat restricted to small-scale fieldoperations.

Fish

Larvivorus fish (Gambusia affinis and Poeciliareticulata) have been extensively used for thecontrol of An. stephensi and/or Ae. aegypti inlarge water bodies or large water containersin many countries in South-East Asia. Theapplicability and efficiency of this controlmeasure depend on the type of containers.

Bacteria

Two species of endotoxin-producing bacteria,Bacillus thuringiensis serotype H-14 (Bt.H-14)and Bacillus sphaericus (Bs) are effectivemosquito control agents. They do not affectnon-target species. Bt.H-14 has been found tobe most effective against An. stephensi and Ae.aegypti, while Bs is the most effective againstCulex quinquefasciatus which breeds in pollutedwaters. There is a whole range of formulatedBti products produced by several majorcompanies for control of vector mosquitoes.Such products include wettable powders andvarious slow-release formulations includingbriquettes, tablets and pellets. Furtherdevelopments are expected in slow-releaseformulations. Bt.H-14 has an extremely low-


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level mammalian toxicity and has beenaccepted for the control of mosquitoes incontainers storing water for household use.

Cyclopoids

The predatory role of copepod crustaceans*was documented between 1930-50, butscientific evaluation was taken up only in1980 in Tahiti, French Polynesia, where it wasfound that Mesocyclops aspericornis couldeffect a 99.3% mortality rate among Aedes(Stegomyia) larvae and 9.7% and 1.9%,respectively among Cx. quinquefasciatus andToxorhynchities amboinensis larvae.(49) Trials incrab burrows against Ae. polynesiensis and inwater tanks, drums, and covered wells metwith mixed results. In Queensland, Australia,out of seven species evaluated in thelaboratory, all but M. notius were found to beeffective predators of both Ae. aegypti and An.farauti but not against Cx. quinquifasciatus.Field releases in both northern and southernQueensland, however, showed mixed results.In Thailand, results were also mixed, but inVietnam, results were more successful,contributing to the eradication of Ae. aegyptifrom one village(50).

Although the lack of nutrients and frequentcleaning of some containers can prevent thesustainability of copepods, they could besuitable for large containers which cannot becleaned regularly (wells, concrete tanks andtyres)(50). They can also be used in conjunctionwith Bt.H-14. Copepods have a role in denguevector control, but more research is required onthe feasibility of operational use.

Autocidal ovitraps

Autocidal ovitraps were successfully used inSingapore as a control device in the eradicationof Ae. aegypti from the Changgi internationalairport. In Thailand, this autocidal trap wasfurther modified as an auto-larval trap usingplastic material available locally. Unfortunately,under the local conditions of water storagepractices in Thailand, the technique was notvery efficient in reducing natural populations ofAe. aegypti. Better results can be expected if thenumber of existing potential larval habitats isreduced, or more autocidal traps are placed inthe area under control, or both activities arecarried out simultaneously. It is believed that,under certain conditions, this technique couldbe an economical and rapid means of reducingthe natural density of adult females as well asserve as a device for monitoring infestations inareas where some reduction in populationdensities of the vector have already taken place.However, the successful application of autocidalovitraps/larval traps depends on the numberplaced, the location of placement, and theirattractiveness as Ae. aegypti female ovipositionsites(51).

8.4 Chemical ControlChemicals have been used to control Ae.aegypti since the turn of the century. In thefirst campaigns against the yellow fever vectorin Cuba and Panama, in conjunction withwidespread clean-up campaigns, Aedes larvalhabitats were treated with oil and houses werefumigated with pyrethrins. When the

____________________________* Copepods should not be used in countries where guineaworm and gnathostomiasis are endemic, as they may act as

intermediate hosts for these parasites.


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insecticidal properties of DDT werediscovered in the 1940s, this compoundbecame a principal method of Ae. aegyptieradication programmes in the Americas.When resistance to DDT emerged in the early1960s, organophosphate insecticides,including fenthion, malathion and fenitrothionwere used for Ae. aegypti adult control andtemephos as a larvicide. Current methods forapplying insecticides include larvicideapplication and space spraying(51).

Chemical larviciding

Larviciding or “focal” control of Ae. aegypti isusually limited to domestic-use containers thatcannot be destroyed, eliminated, or otherwisemanaged. It is difficult and expensive to applychemical larvicides on a long-term basis.Therefore chemical larvicides are best used insituations where the disease and vectorsurveillance indicate the existence of certainperiods of high risk and in localities whereoutbreaks might occur. Establishing the precisetiming and location are essential for maximumeffectiveness. Control personnel distributingthe larvicide should always encourage houseoccupants to control larvae by environmentalsanitation. There are three insecticides thatcan be used for treating containers that holddrinking water.

Temephos 1% sand granules

One per cent temephos sand granules areapplied to containers using a calibrated plasticspoon to administer a dosage of 1 ppm. Thisdosage has been found to be effective for 8-12weeks, especially in porous earthen jars, undernormal water use patterns. The quantity of sand

granules required to treat various size watercontainers is shown in Annex VIII. Althoughresistance to temephos in Ae. aegypti and Ae.albopictus populations has not been reportedfrom the South-East Asia Region, thesusceptibility level of Aedes mosquitoes shouldbe monitored regularly in order to ensure theeffective use of the insecticide.

Insect growth regulators

Insect growth regulators (IGRs) interfere withthe development of the immature stages ofthe mosquito by interference of chitinsynthesis during the molting process in larvaeor disruption of pupal and adulttransformation processes. Most IGRs haveextremely low mammalian toxicity (LD50value of acute oral toxicity for methoprene(Altosid) is 34 600 mg/kg). In general, IGRsmay provide long-term residual effects (threeto six months) at relatively low dosages whenused in porous earthen jars. Because IGRs donot cause immediate mortality of theimmature mosquitoes, countries withlegislation stipulating that the breeding ofAedes larvae is an offense, will require somealteration of the law, so as not to penalizehome owners who use these compounds.

Bacillus thuringiensis H-14 (Bt.H-14)

Bt.H-14, which is commercially availableunder a number of trade names, is a proven,environmentally-nonintrusive mosquitolarvicide. It is entirely safe for humans whenthe larvicide is used in drinking water innormal dosages(52). Slow-release formulationsof Bt.H-14 are being developed. Briquetteformulations that appear to have greater


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residual activity are commercially availableand can be used with confidence in drinkingwater. The use of Bt.H-14 is described in thesection on biological control. The largeparabasal body that forms in this agentcontains a toxin that degranulates solely in thealkaline environment of the mosquito midgut.The advantage of Bt.H-14 is that anapplication destroys larval mosquitoes butspares any entomophagus predators and othernon-target species that may be present. Bt.H-14 formulations tend to rapidly settle at thebottom of water containers, and frequentapplications are therefore required. The toxinis also photolabile and is destroyed bysunlight.

Space sprays

Space spraying involves the application ofsmall droplets of insecticide into the air in anattempt to kill adult mosquitoes. It has beenthe principal method of DF/DHF control usedby most countries in the Region for 25 years.Unfortunately, it has not been effective, asillustrated by the dramatic increase in DHFincidence in these countries during the sameperiod of t ime. Recent studies havedemonstrated that the method has little effecton the mosquito population, and thus ondengue transmission (53,54,55). Moreover, whenspace spraying is conducted in a community,it creates a false sense of security amongresidents, which has a detrimental effect oncommunity-based source reductionprogrammes. From a political point of view,however, it is a desirable approach becauseit is highly visible and conveys the messagethat the government is doing something about

the disease. This, however, is poor justificationfor using space sprays. The currentrecommendations are that space spraying ofinsecticides (fogging) should not be usedexcept in the most extreme conditions duringa major DHF epidemic. However, theoperations should be carried out at the righttime, at the right place, and according to theprescribed instructions with maximumcoverage, so that the fog penetration effect iscomplete enough to achieve the desiredresults.When space sprays are employed, it isimportant to follow the instructions on boththe application equipment and the insecticidelabel and to make sure the applicationequipment is well maintained and properlycalibrated. Droplets that are too small tend todrift beyond the target area, while largedroplets fall out rapidly. Nozzles for ultra-lowvolume ground equipment should be capableof producing droplets in the 5 to 27 micronrange and the mass median diameter shouldnot exceed the droplet size recommended bythe manufacturer. Desirable spraycharacteristics include a sufficient period ofsuspension in the air with suitable drift andpenetration into target areas with the ultimateaim of impacting adult mosquitoes. Generally,there are two forms of space-spray that havebeen used for Ae. aegypti control, namely“thermal fogs” and “cold fogs”. Both can bedispensed by vehicle-mounted or hand-operated machines.

Thermal fogs

Thermal fogs containing insecticides arenormally produced when a suitable


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formulation condenses after being vaporizedat a high temperature. Generally, a thermalfogging machine employs the resonant pulseprinciple to generate hot gas (over 200oC) athigh velocity. These gases atomize theinsecticide formulation instantly so that it isvaporized and condensed rapidly with onlynegligible formulation breakdown. Thermalfogging formulations can be oil-based orwater-based. The oil(diesel)-basedformulations produce dense clouds of whitesmoke, whereas water-based formulationsproduce a colorless fine mist. The droplet(particle) size of a thermal fog is usually lessthan 15 microns in diameter. The exactdroplet size depends on the type of machineand operational conditions. However, uniformdroplet size is difficult to achieve in normalfogging operations.

Ultra-low volume (ULV), aerosols (coldfogs) and mists

ULV involves the application of a smallquantity of concentrated liquid insecticides.The use of less than 4.6 litres/ha of aninsecticide concentrate is usually consideredas an ULV application. ULV is directly relatedto the application volume and not to thedroplet size. Nevertheless, droplet size isimportant and the equipment used should becapable of producing droplets in the 10 to 15micron range, although the effectivenesschanges little when the droplet size range isextended to 5-25 microns. The droplet sizeshould be monitored by exposure on teflonor silocone-coated slides and examined undera microscope. Aerosols, mists and fogs may beapplied by portable machines, vehicle-mounted generators or aircraft equipment.

House-to-house application usingportable equipment

Portable spray units can be used when thearea to be treated is not very large or in areaswhere vehicle-mounted equipment cannot beused effectively. This equipment is meant forrestricted outdoor use and for enclosed spaces(buildings) of not less than 14m3. Portableapplication can be made in congested low-income housing areas, multistoried buildings,godowns and warehouses, covered drains,sewer tanks and residential or commercialpremises. Operators can treat an average of80 houses per day, but the weight of themachine and the vibrations caused by theengine make it necessary to allow theoperators to rest, so that two or threeoperators are required per machine.

Vehicle-mounted fogging

Vehicle-mounted aerosol generators can beused in urban or suburban areas with a goodroad system. One machine can cover up to1500-2000 houses (or approximately 80 ha)per day. It is necessary to calibrate theequipment, vehicle speed, and swath width(60-90m) to determine the coverage obtainedby a single pass. A good map of the areashowing all roads is of great help in undertakingthe application. An educational effort may berequired to persuade the residents tocooperate by opening doors and windows.

The speed of the vehicle and the time ofday of application are important factors toconsider when insecticides are applied byground vehicles. The vehicle should not travelfaster than 16 kph (10 mph). When the windspeed is greater than 16 kph or when the


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ambient air temperature is greater than 28oC(82oF), the insecticide should not beapplied(25). The best time for application is inthe early morning (approximately 0600-0830hours) or late afternoon (approximately 1700-1930 hours). For details of procedures, timing,frequency of thermal fogging and ULV spaceoperation please see Annex IX.

Performance of fogging machines

Estimates have been made of the averagecoverage per day with certain aerosol andthermal fog procedures (Box 19).

Insecticide formulations for spacesprays

Organophosphate insecticides, such asmalathion, fenitrothion and pirimiphos methylhave been used for the control of adult Aedesvectors. Undiluted technical grade malathion(active ingredient 95%+) or one part technicalgrade diluted with 24 parts of diesel havebeen used for ULV spraying and thermalfogging respectively. For undiluted technicalgrade ULV malathion applications fromvehicles, the dosage on an area basis is 0.5liters per hectare.

Apart from the above-mentionedformulations, a number of companies producepyrethroid formulations containing eitherpermethrin, deltamethrin, lambda-cyhalothinor other compounds which can be used forspace spray applications. It is important notto under-dose during operational conditions.Low dosages of pyrethroid insecticides areusually more effective indoors than outdoors.

Also, low dosages are usually more effectivewhen applied with portable equipment (closeto or inside houses) than with vehicle-mounted equipment, even if wind andclimatic conditions are favourable for outdoorapplications. Outdoor permethrin applicationswithout a synergist should be applied atconcentrations ranging from 0.5% to 1.0%,particularly in countries with limited resourcesand a lack of staff experienced in routinespraying operations. Regardless of the type ofequipment and spray formulations andconcentrations used, an evaluation should bemade from time to time to ensure thateffective vector control is being achieved.Insecticides suitable as cold aerosols andthermal fogging for mosquito control areincluded in Annex X.

Box 19Average coverage per day with

space spraying procedures

Equipment Possible dailycoverage

1. Vehicle-mountedcold fogger 225 ha

2. Vehicle-mountedthermal fogger 150 ha

3. Back-pack ULVmist blower 30 ha

4. Hand carried thermalfogger. Swing fog 5 ha

5. Hand carried ULV 5 ha oraerosol generators 250 houses


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Integrated control approach

The use of insecticides for the prevention andcontrol of dengue vectors should be integratedinto environmental methods whereverpossible. During periods of little or no denguevirus activity, the routine source reductionmeasures described earlier can be integratedinto larvicide application in containers thatcannot be eliminated, covered, filled orotherwise managed. For emergency control tosuppress a dengue virus epidemic or toprevent an imminent outbreak, a programmeof rapid and massive destruction of the Ae.aegypti population should be undertaken withboth insecticides and source reduction, usingthe techniques described in these guidelinesin an integrated manner.

Insecticide susceptibility monitoring

During the past 40 years, chemicals have beenwidely used to control mosquitoes and otherinsects from spreading diseases of publichealth importance. As a result, Ae. aegypti andother dengue vectors in several countries have

developed resistance to commonly-usedinsecticides, including temephos, malathion,fenthion, permethrin, propoxur andfenitrothion. It is therefore advisable to obtainbaseline data on insecticide susceptibilitybefore insecticidal control operations arestarted, and to continue monitoringsusceptibility levels periodically. WHO kits areavailable for testing the susceptibility of adultand larval mosquitoes and other arthropodvectors to commonly-used insecticides. Thesecan be obtained from the CommunicableDiseases Cluster, World Health Organization,1211 Geneva 27, Switzerland, or throughWHO Regional Offices or WHORepresentatives in the countries.

Safety precautions for chemical control

All pesticides are toxic to some degree. Safetyprecautions should therefore be followed,including care in the handling of pesticides,safe work practices for those who apply them,and their appropriate use in and aroundoccupied housing. A safety plan for insecticideapplication is included in Annex XI.

Sustainable Preventionand Control Measures

9.1 Community ParticipationCommunity participation (CP) has beendefined “as a process whereby individuals,families and communities are involved in theplanning and conduct of local vector controlactivities so as to ensure that the programmemeets the local needs and priorities of thepeople who live in the community, andpromotes community’s self-reliance in respectto development.” In short, CP entails thecreation of opportunities that enable allmembers of the community and extendedsociety to actively contribute to, influence thedevelopment of, and share equitably in thefruits of accrued benefits.

Objectives of community participationin dengue prevention and control

(1) To extend the coverage of the programmeto the whole community by creatingcommunity awareness. This however oftenrequires intensive inputs.(2) To make the programme more efficientand cost-effective, with greater coordination

of resources, activities and efforts pooled bythe community.(3) To make the programme more effectivethrough joint community efforts to set goals,objectives and strategies for action.(4) To promote equity through sharing ofresponsibility, and through solidarity in servingthose in greatest need and at greatest risk .(5) To promote self-reliance amongcommunity members and increase their senseof control over their own health and destiny.

How to invoke community participation

By showing concernCommunity and government organizersshould reflect the true concern for humansuffering, i.e. morbidity and mortality due todengue in the country, economic losses to thefamilies and the country, and how the benefitsof the programme fit into the people’s needsand expectations.

Initiating dialogue

Community organizers and opinion leaders orother key personnel in the power structure of

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the community, namely women’s groups,youth groups and civic organizations, shouldbe identified. Dialogue should be undertakenthrough personal contacts, group discussionsand film shows. Interaction should generatemutual understanding, trust and confidence,enthusiasm and motivation. The interactionshould not be a one-time affair, but should bea continuing dialogue to achieve sustainability.

Creating community ownership

Organizers should use community ideas andparticipation to initiate the programme,community leaders to assist the programme,and community resources to fund theprogramme. Mosquito control, abatementagency and community partnerships shouldbe strong, but limited to providing technicalguidance and expertise.

Health education (HE)

Health education should not be based on tellingpeople the do’s and don’ts through a vertical,top-down communication process. Instead,health education should be based on formativeresearch to identify what is important to thecommunity and should be implemented atthree levels, i.e. the community level, systemslevel and political level.

Community level

People should not only be provided withknowledge and skills on vector control, buteducation materials should empower themwith the knowledge that allows them to makepositive health choices and gives them theability to act individually and collectively.

Systems level

To enable people to mobilize local actions andsocietal forces beyond a single community, i.e.health, development and social services.

Political level

Mechanisms must be made available to allowpeople to articulate their health priorities topolitical authorities. This will facilitate placingvector control high on the priority agenda andeffectively lobby for policies and actions.

Defining community actions

For sustaining DF/DHF prevention and controlprogrammes, the following community actionsare essential(56):(1) At the individual level, encourage eachhousehold to adopt routine health measuresthat will help in the control of DF and DHF,including source reduction and implementa-tion of proper personal protection measures.(2) At the community level, organize “clean-up” campaigns two or more times a year tocontrol the larval habitats of the vectors inpublic and private areas of the community.Some key factors for the success of suchcampaigns include extensive publicity viamass media, posters and pamphlets, properplanning, pre-campaign evaluation of foci,execution in the community as promised, andfollow-up evaluations. Participation bymunicipal sanitation services should bepromoted.(3) Where community-wide participation isdifficult to arrange for geographical,occupational or demographic reasons,participation can be arranged through

Sustainable Prevention and Control Measures

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voluntary associations and organizations. Thepeople in these organizations may interactdaily in work or institutional settings, or cometogether for special purposes, i.e. religiousactivities, civic clubs, women’s groups andschools.(4) Emphasize school-based programmestargeting children and parents to eliminatevector breeding at home and at school.(5) Challenge and encourage the privatesector to participate in the beautification andsanitary improvement of the community assponsors, emphasizing source reduction ofdengue vectors.(6) Combine community participation inDHF prevention and control with otherpriorit ies of community development.Where municipal services (such as refusecollection, wastewater disposal, provision ofpotable water, etc.) are either lacking orinadequate, the community and theirpartners can be mobilized to improve suchservices, and at the same time reduce thelarval habitats of Aedes vectors as part ofan overal l ef fort at communitydevelopment.(7) Combine dengue vector control with thecontrol of all species of disease-bearing andnuisance mosquitoes as well as other vermin,to ensure greater benefits for the communityand consequently greater participation inneighbourhood campaigns.(8) Arrange novel incentives for those whoparticipate in community programmes fordengue control. For example, a nationwidecompetition can be promoted to identifythe cleanest communities or those with thelowest larval indices within an urban area.

Detailed requirements for sustainableparticipation in a vector-borne disease controlprogramme are presented in Annex XII.

9.2 Intersectoral CoordinationDeveloping economies in countries of theSouth-East Asia Region have recognizedmany social, economic and environmentalproblems which promote mosqui tobreeding. The dengue problem thusexceeds the capabilities of ministries ofhealth. The prevention and control ofdengue requires close collaboration andpartnerships between the health and non-health sectors (both government andprivate), nongovernmental organizations(NGOs) and local communities. Duringepidemics such cooperation becomes evenmore critical, since it requires pooling ofresources from all groups to check the spreadof the disease. Intersectoral cooperationinvolves at least two components :(i) resource-shar ing, and ( i i) policyadjustments among the various ministriesand nongovernmental sectors.

Resource sharing

Resource shar ing should be soughtwherever the dengue control coordinatorcan make use of underutilized humanresources, e.g. for local manufacture ofneeded too l s , seasona l governmentlabourers for water supply improvementactivities, or community and youth groupsto clean up discarded tyres and containersin neighbourhoods.


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Policy adjustment

The dengue control programme should seekthe accommodation or adjustment of existingpolicies and practices of other ministries,sectors, and municipal governments to includepublic health as a central focus for their goals.For instance, the public works sector could beencouraged to adjust its policies to give firstpriority to water supply improvements forcommunities at highest risk of dengue. Inreturn, the Ministry of Health could authorizethe use of some of its field staff to assist theministry responsible for public works to repairwater supply and sewerage systems in otherurban areas.

Role of non-health sectors in denguecontrol

The following examples show how severalgovernment ministries may contribute todengue vector control efforts.

Role of the ministry responsible forpublic works

The ministry responsible for public works andits municipal counterparts should play a keyrole in dengue control. They can contributeto source reduction by providing a safe,dependable water supply, adequatesanitation, and effective solid wastemanagement. In addition, through theadoption and enforcement of housing andbuilding codes, a municipality may mandatethe provision of utilities such as individualhousehold piped water supplies or sewerageconnections, and rainwater (stormwater) run-

off control for new housing developments, orforbid open surface wells.

Role of the Ministry of Education

The Ministry of Health should work closelywith the Ministry of Education to develop ahealth education (health communication)component targeted at school children, anddevise and communicate appropriate healthmessages. Health education models can bejointly developed, tested, implemented andevaluated for various age groups. Researchprogrammes in universities and colleges canbe encouraged to include components thatproduce information of direct importance(e.g. vector biology and control, casemanagement) or indirect importance (e.g.improved water supply, educational inter-ventions to promote community sanitation,waste characterization studies) to denguecontrol programmes.

Role of the ministry responsible for theenvironment

The Ministry of Environment can help theMinistry of Health collect data and informa-tion on ecosystems and habitats in or aroundcities at high risk of dengue. Data andinformation on local geology and climate, landusages, forest cover, surface waters, andhuman populations are useful in planningcontrol measures for specific ecosystems andhabitats. The Ministry of Environment mayalso be helpful in determining the beneficialand adverse impacts of various Ae. aegypticontrol tactics (chemical, environmental andbiological).


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Role of the ministry responsible forinformation, communication andthe mass media

Information directed at the community atlarge is best achieved through the mass media,such as television, radio and newspapers.Therefore, the ministry responsible forinformation, communication and the massmedia should be approached to coordinatethe release of messages on the prevention andcontrol of dengue developed by public healthspecialists.

Role of nongovernmentalorganizations (NGOs)

NGOs can play an important role inpromoting community participation andimplementing environmental management fordengue vector control. This will most ofteninvolve health education, source reduction,and housing improvement related to vectorcontrol. Community NGOs may be informalneighbourhood groups or formal privatevoluntary organizations, service clubs, churchesor other religious groups, or environmental andsocial action groups.

After proper training by the Ministry ofHealth staff in source reduction methods,NGOs can collect discarded containers (tyres,bottles, tins, etc.), clean drains and culverts,fill depressions, remove abandoned cars androadside junk, and distribute sand or cementto fill treeholes. NGOs may also play a keyrole in the development of recycling activitiesto remove discarded containers from yardsand streets. Such activities must becoordinated with the environmental sanitationservice.

NGOs may also be able to play a specific,but as yet unexplored, role in environmentalmanagement during epidemic control. Underguidance from the Ministry of Health, NGOscould concentrate on the physical control oflocally identified, key breeding sites such aswater drums, waste tyre piles, and cemeteryflower vases.

Service clubs such as Rotary Internationalhave supported DF/DHF prevention andcontrol programmes in the American Regionfor over 15 years (57). In Asia and the Pacific,programmes have been initiated in Sri Lanka,Philippines, Indonesia and Australia to provideeconomic and political support for successfulcommunity-based campaigns. A new grantfrom the Rotary Foundation of RotaryInternational has been awarded to study thepossibility of upscaling this project to a globalprogramme. Women’s clubs have contributedto Ae. aegypti control by conductinghousehold inspections for foci and carryingout source reduction. There are manyopportunities, mostly untapped, forenvironmental organizations and religiousservice groups to play similar roles in eachAe. aegypti-infested community.

9.3 Model DevelopmentModel development for dengue controlthrough a community participation approachshould be initiated in order to define potentialprime movers in the communities and tostudy ways to persuade them to participate invector control activities. Social, economic andcultural factors that promote or discourage theparticipation of these groups should be


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intensively studied in order to gain moreparticipation from the community. Modeldevelopment focusing on school children hasbeen studied in several countries and thisstrategy should be modified and introducedinto each country.

9.4 Social MobilizationAdvocacy meetings should be conducted forpolicy makers to attain political commitmentfor mass clean-up campaigns andenvironmental sanitation. Intersectoralcoordination meetings should be conductedto explore possible donors for mass antilarvalcontrol campaigns and measures and to helpfinance the programme. Reorientation trainingof health workers should be conducted toimprove their technical capability and abilityto supervise prevention and control activities.A “DHF month” should be identified twice ayear, during the pre-transmission season andduring the peak transmission period.

9.5 Health EducationHealth education is very important inachieving community participation. It is along-term process to achieve humanbehavioural change, and thus should becarried out on a continuous basis. Eventhough countries may have limited resources,health education should be given priority inendemic areas and in areas at high risk forDHF. Health education is conducted throughthe different channels of personalcommunication, group educational activities,and mass media. Health education can be

implemented by women’s groups, schoolteachers, formal and informal communityleaders, and health workers. Health educationefforts should be intensified before the periodof dengue transmission as one of thecomponents of social mobilization. The maintarget groups are school children and women.

9.6 Legislative SupportLegislative support is essential for the successof dengue control programmes. All countriesof the Region have legislation addressingcontrol of epidemic diseases which authorizehealth officers to take necessary action withinthe community for the control of epidemics.On a continuous and sustainable basis, variousmunicipalities have adapted legislation for theprevention of “nuisance mosquitoes”,however they lack specific provision relatedto dengue and/or Ae. aegypti control. At thenational level, all countries are signatories tothe International Health Regulations whichhave a specific provision for the control of Ae.aegypti and other disease vectors aroundinternational sea/airports.

The formulation of legislation on dengue/Ae.aegypti control should, therefore, take intoconsideration the following points:(1) Legislation should be a necessarycomponent of all dengue/Ae.aegyptiprevention and control programmes.(2) All existing decrees and resolutions ondengue/Ae.aegypti prevention and controlmust be reviewed, and their effectivenessevaluated in terms of structural, institutionaland administrative changes. It is alsoimportant to add dengue to the list of diseases


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that require mandatory notification in eachcountry.(3) Regulations should be formulated on thebasis of existing sanitary codes, a strategy thatis most needed in those countries which lacklegislation on the subject. In countries wheresanitary regulations are primarily theresponsibility of agencies other than theMinistry of Health (e.g. municipalgovernments), a coordinated and cooperativeline of action with the ministry should bedeveloped.(4) Legislation should incorporate municipalauthorities from affected regions as the centralelement for implementation and enforcement.Where national legislation is weak or absent,municipal governments may consider theadoption of local ordinances for Ae. aegypticontrol.(5) Legislation should contemplateintersectoral coordination among theministries involved in national development inorder to prevent isolated implementation ofindividual programmes and harmfulenvironmental changes that could createpotentially hazardous public healthconditions. Ministries should be advised onthe best ways to encourage diseaseprevention.(6) Legislation should cover all aspects ofenvironmental sanitation in order to effectivelycontribute to the prevention of alltransmissible diseases.(7) Laws should contemplate the existingjudicial administrative framework in thecontext of national public administration.Importance should also be placed on norms

aimed at developing human resources withinthe institutional framework.(8) In developing legislation, the socialcomponent must be considered. Legislationshould seek support based on justice andjustification: individuals and the communitymust be persuaded that the law is good andthat it is intended to protect them and theirfamilies, and that compliance with it is oneof the most important components for denguecontrol (Box 20).

Box 20Examples of other enforcement

methods that may be considered

l Ordinances that require mosquito-proofing of cisterns, water-storagetanks, wells and septic tanks.

l Ordinances that authorize theremoval of junk cars and otherscrap, after proper notification.

l Ordinances that authorize theposting of “No Dumping” and “NoLittering” signs and civil penalties forviolators.

l Ordinances that require house-owners to keep their yards free ofjunk, litter, and potential foci, underthreat of civil penalty.

l Ordinances requiring mandatoryhousehold collection of solid wastesfor all neighbourhoods.

l Statutes/laws that require certifica-tion of imported tyres as being dryand pest-free upon arrival at ports.

Evaluation of DF/DHF Preventionand Control Programmes

IT is essential to monitor and evaluate theprogress of DF/DHF prevention andcontrol programmes. They enable the

programme manager to assess theeffectiveness of control initiatives and must becontinuous operational processes. The specificobjectives of programme evaluation are:l to measure progress and programme

achievements,l to detect and solve problems,l to assess programme effectiveness and

efficiency,l to guide the allocation of programme

resources,l to collect information needed for revising

policy and replanning interventions, andl to assess the sustainability of the

programme.

10.1 Types of Evaluation(58)

There are two types of evaluation:(1) Monitoring(2) Formal evaluation

Monitoring

Monitoring or concurrent evaluation involvesthe continuous collection of informationduring programme implementation. It allowsimmediate assessment and identification ofdeficiencies that can be rectified withoutdelaying the programme’s progress.Monitoring provides the type of feedbackwhich is important to programme managers.

Most monitoring systems follow thequantity and timings of various programmeelements such as activities undertaken, staffmovements, service utilization, supplies andequipment, and budgeting. Focus should alsobe made on the process of implementation ofthe dengue control strategy in time and spaceand the quality of implementation, seekingreasons for successes and failures.

Monitoring should be undertaken bypersons involved in the programme at variouslevels. This exercise by programme managerswill give a better and deeper understandingof the programme’s progress, strengths andweaknesses. The information collected should

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help programme managers strengthen theweaker links and optimize output.

Formal evaluation

In addition to regular monitoring, which isgenerally built-in, there is also a need for moreformal evaluation at different intervals toobtain a precise picture of programmeprogress. This type of evaluation is even moreessential when the programme is failing toachieve its targets or goals or when it hasbecome static. This type of special evaluationshould be done systematically and should takeinto account all programme elements. Themain idea of such a study is to determinewhether the programme is moving towards itstargets and goals, to identify new needs,particularly for increased inputs (e.g.additional manpower, money, materials, IECactivities, capacity building), and to identifyoperational research areas for maximumoperationalization.

Formal evaluation, therefore, shouldsystematically assess the elements outlinedbelow. However, the evaluation can cover oneor more other processes depending on theobjectives of the evaluation.l Evaluation of need, i.e. evaluation of the

relative need for the programme.l Evaluation of plans and design, i.e. evalua-

tion of the feasibility and adequacy ofprogramme plans or proposals.

l Evaluation of implementation, i.e. evalua-tion of the conformity of the programmeto its design. Does the programme providethe goods and services laid down in theplan, in both quality and quantity?

l Evaluation of outcomes, i.e. evaluation ofthe more immediate and direct effects ofthe programme on relevant knowledge,attitudes and behaviour. For trainingactivities, for example, outcome measuresmight relate to the achievement oflearning objectives and changes in staffperformance.

l Evaluation of impact, i.e. evaluation of theprogramme’s direct and indirect effectson the health and socioeconomic statusof individuals and the demography of thecommunity.

10.2 Evaluation PlansAn evaluation plan should have realistic andassessable targets. With this proviso, thedevelopment of an evaluation plan consists ofthe following steps:l Clarification of the objectives of the

evaluation – these must be agreed uponby all concerned.

l Identification of the resources available –there must be sufficient resources tocollect the data on the scale envisaged andturn them into useful information.

l Selection of the type of evaluation – oncethe purpose of the evaluation is clear, it isnecessary to decide the type of evaluationand the depth of information required.

l Selection of indicators – a good indicatoris directly related to programme activitiesand anticipated outcomes. Therefore,indicators chosen should be limited innumber, readily and uniformly inter-pretable, and operationally useful. Forcomparison purposes, use of standard

Evaluation of DF/DHF Prevention and Control Programme

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indictors will introduce consistency intoprogramme reviews and allowcomparison over time and amongcountries. Although there are many waysof classifying indicators, one useful way isaccording to the programme structureoutlined in Box 21. Thus, there can beinput, process, outcome and impactindicators.

l Formulation of the detailed evaluation plan– the detailed plan should include theobjectives, methods, sampling procedures,source of data, and methods of data analysisto be used, as well as budgeting andadministrative arrangements. It should alsogive details of staff responsibilities for eachactivity, the reporting mechanism, and thestrategies for ensuring that results are usedfor programme replanning andimplementation.

l Collection of data – the objective of thisstep is to ensure that procedures arefollowed in such a way that data arecollected in a reliable and timely manner.

l Interpretation and analysis of data –decisions about the main approaches todata analysis will have been made whenthe indicators were selected and thedetailed plan was formulated.

l Replanning – at this step the results of theevaluation are fed back into themanagerial process. Unfortunately, it isoften this replanning step that is done theleast well.

10.3 Cost-Effective EvaluationIn most countries of the Region, it is difficultto estimate how much money dengueprevention and/or control programmes spendannually. Often, dengue or Aedes controlprogrammes function as branches of malariacontrol programmes and/or operatesporadically in response to real or perceivedemergencies. Supplies, equipment andpersonnel are not continuously available. Inemergencies, or under public pressure,expenditures of national funds or donations

Box 21Aspects of a programme that can be evaluated

Inputs

• buildings• staff• finance• equipment• supplies

Processes

• training• planning• management• supervision• community

participation

Outputs

• servicesdelivered

• goodsdelivered

• staff trained

Outcomes

• changes inknowledge

• changes inpractice andbehaviour

Impact

• changes inhealthsituation


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can be very high, especially for insecticides,while little money is available for routineoperations at other times.

As a result, substantial funds are spent onunstructured activities, the results of which aredifficult or impossible to evaluate. It istherefore important that economic factors beconsidered during the reorganization orstrengthening of dengue control programmes.Information of this nature is essential forplanning, for evaluating the cost-effectivenessof individual control measures, for comparingdifferent control measures, and for evaluatingnew methods. Examples of types of costestimates that should be obtained aredescribed below.

(a) Vector control costs

Operational costs

It is not enough to merely estimate thequantities of insecticide required. Costingshould begin with the size of the populationto be protected and the number of premisesor the area to be treated, as well as thepersonnel requirements (at all levels) based onthe frequency of application. Personnel costsinclude expenditures on training, safetyequipment, and per diem or overtime whereapplicable. Initial capital costs for equipment,depreciation and/or shared usage with otherprogrammes must also be considered.Operational costs, especially for ULV spacespraying, should include machinery andvehicle maintenance, regular calibration ofpumps, as well as the costs of monitoringvector populations, penetration of droplets,and the level of compliance by the local

population, depending on the controlmeasures employed. The compilation andanalysis of data also involve costs.

Environmental management

Source reduction programmes are oftenconsidered less expensive alternatives tochemical control measures. However, this mayonly be true for short-term “clean up”campaigns. Long-term success inenvironmental management requires healtheducation, public health communication, anddevelopment of community cooperation.Educational materials, promotion through themedia, introduction of sanitary concepts intoschool curricula, training of teachers, etc. mayinvolve considerable costs. Some of thesecosts can be covered by other sectors such aseducation, municipal or private, and suchcollaboration should be encouraged.

Environmental management campaigns,especially clean-up campaigns, may fail fromlack of transport and facilities for solid wastedisposal. Communities, especially cities, needeither to invest in such equipment or makearrangements to rent or borrow it from othersources. As with chemical control,environmental management programmesmust be evaluated and the vector and diseasedata organized and analysed. All of theseactivities involve costs.

(b) Laboratory surveillance

Most national laboratories that performserology or virus isolation for other agents(measles, polio, etc.) can also include dengue.The cost of the dengue component must be


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adequately assessed based on an analysis ofthe number of samples processed, the cost ofreagents, and the equipment required. Long-term investment must be made andaccounted for in the training of professionalsand technicians. Refresher training sessionsneed to be routinely scheduled.

(c) Coordination with hospitals andmedical supplies

In addition to coordination among itscomponent parts, the programme requirescoordination between curative and preventiveservices and these expenses should berecognized. An information exchange networkis also required. In order to meet the potentialfor epidemic situations, hospital supplies andequipment must be readily available and bereplaced and/or updated regularly.

Each country should estimate the costsassociated with individual case management.Through cooperation with and informationfrom neighbouring countries and internationalorganizations, it should estimate itsrequirements on an annual or biennial basis.

(d) Surveillance

Guidelines for entomological andepidemiological surveillance methods aregiven in the chapter on surveillance. Thesecan be used as a framework for estimating thesize of the required surveillance system in agiven city, state, province or country, as wellas the cost of the surveillance that, in additionto laboratory costs and information exchange,includes expenditures for collecting andprocessing samples in the field.

(e) Community participation, healtheducation and communicationcosts

In addition to the costs that have already beenmentioned, liaison must be established withcommunity groups. This is in order to providetechnical assistance where required and todetermine how the health authorities canassist these groups with their individual andcollective efforts. Health education andcommunication activities will play a significantrole in community participation efforts.Consequently, it is extremely important toestimate their cost. The calculation of actualcosts of health education, communication andcommunity participation should also be madeon an annual basis.

(f) Social and economic impact

The social and economic burden of DF/DHFis another element to be considered whendetermining the cost-effectiveness of DHFcontrol. In a 1995 study carried out by theFaculty of Tropical Medicine of MahidolUniversity in Thailand(59), in collaboration withthe Faculty of Economics of ChulalongkornUniversity in Bangkok, Thailand, severalparameters [treatment-seeking behaviour,direct impact, i.e. cost of the illness of patients(average 7.9 days) and time-cost spent byparents/caretakers (average 9.5 days), andindirect impact due to disruption of family liferesulting in increased expenses] wereidentified. From the provider side,expenditures for the hospitalization of DHFpatients included drug, laboratory and nursingcosts and the cost of prevention and control.


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The estimated costs for these items areprovided in Box 22.

Another approach is to measure thedisability-adjusted life years (DALYs) associatedwith dengue infection. A recent study inPuerto Rico showed a constant increase in theDALYs associated with dengue infection from1984 to 1994(60,61). Surprisingly, the DALYsassociated with dengue infection in PuertoRico were of the same order of magnitude asthe DALYs caused by a number of otherinfectious diseases in Latin America, includingmalaria, tuberculosis, sexually transmitted

diseases (excluding HIV/AIDS), hepatitis, thechildhood cluster and the tropical cluster.

(g) Other costs

Each national programme will have additionalcost elements depending on the governmentalstructure and the requirements of theiraccounting systems. These may includedepreciating capital investments (vehicles,pumps, etc.), shared use of faci l i t ies(warehouses, administrative services, etc.),and in-country purchase and delivery ofsupplies (insecticides).

Box 22Costs of DHF control in Thailand (58)

US$1. Cost due to morbidity (per patient)

User cost : total patient cost Child 113.0Adult 154.6

Provider cost : hospitalization 44.0

Total morbidity cost Child 157.0Adult 198.6

2. Cost due to mortality (per patient)Funeral cost Child 395.0

Adult 648.0Potential income loss (50 working years) 120,000.0

Total mortality cost Child 120,395.0Adult 120,648.0

3. Cost for prevention and control in 1994Ministry of Public Health annual budget 1,868,968.0Bangkok Municipality Administration annual budget 112,000.0Ministry of Interior (75 provinces,est. 0.25 million/province) 2,891,400.0

Total prevention and control cost 4,872,368.0

Note: Costs from providers do not include salaries, administration and supportive expenditures.


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Once the costs of the components ofindividual dengue control projects have beendetermined, it will not only be possible toestimate total costs, but also to identify wheresavings may be gained through collaborationwith other government agencies and theprivate sector. The cost data collected, alongwith the epidemiological and entomologicaldata, provide an initial framework forconducting cost-effectiveness studies of the

different interventions used in the nationalprogramme. New methods and improvementsof existing methods can be more effectivelyevaluated for operational use when theireconomic benefits or limitations are fullyunderstood. The benefits to dengue controlprogrammes should be considered in the lightof social and economic considerations as wellas the health impact of epidemics.

The Regional Strategy forthe Prevention and Control

of DF/DHF11.1 Basic ElementsThe basic elements of the regional strategy

(62)

are to:(1) Establish effective disease and vector

surveillance systems based on reliablelaboratory and health information systems.

(2) Undertake disease prevention throughselective, stratified and integrated vectorcontrol with community and intersectoralparticipation.

(3) Establish emergency preparednesscapacity to prevent and control outbreakswith appropriate contingency plans forvector control, hospitalization, educationand adequate logistics.

(4) Ensure prompt case management ofDHF/DSS, including early recognition ofthe signs and symptoms, to prevent casemortality.

(5) Strengthen capacity and promote training,health education, and research onsurveillance, vector control, laboratorydiagnosis and case management(see Box 23).

Strategy requirements

(1) Recognition of DF/DHF as an importanthealth problem in endemic countries.

(2) Decison to include DF/DHF in the list ofreportable diseases for all endemiccountries.

(3) Long-term political commitment fromgovernments and multisectoralinvolvement.

Box 23Regional Strategy

l Effective disease and vectorsurveillance

l Selective and stratified integratedvector control through communityparticipation

l Emergency preparedness andresponse

l Clinical diagnosis and prompt case-management

l Capacity building and promotion oftraining and research

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(4) Sustainable national financial support toDF/DHF prevention and controlprogrammes in the context of health careand overall development.

(5) Development of national plans of actionwith realistic and clear objectives andtargets to reduce DHF mortality anddengue morbidity.

(6) Development of monitoring systems fordisease activity and vector distribution anddensity, through improved surveillancewhich must include clinical, laboratory andentomological components.

(7) Support to health services to ensure earlydiagnosis and prompt treatment of DHF/DSS cases.

(8) Development of national capacity forundertaking selective and sustainablevector control and other preventivemeasures within the health and othersectors, as well as within the community.

(9) Development of national capacity toundertake research related to the vectorand the epidemiology and laboratorydiagnosis of the infection.In order to ensure their sustainability,

national strategies for the prevention andcontrol of DF/DHF should be made a part ofthe existing infrastructure of infectious diseasecontrol programmes and should be based onlarval source reduction. The communityshould actively participate in control activities,particularly in eliminating vector breedingsources.

11.2 National Dengue ControlProgrammes in South-EastAsian Countries

In several countries of the Region where DHFis prevalent, national dengue control

programmes have existed for several decades.In others, where DHF is a newly emergentdisease, there are no existing controlprogrammes.In Indonesia, the national dengue controlprogramme started in 1974 and graduallyexpanded to become an integral part ofgeneral health services in the context ofprimary health care. In Thailand, controlmeasures were confined to high-risk areasuntil 1974, when a national campaign fordengue control was established. The verticallystructured programme was later integratedinto local health services with logisticssupplied at the central level. Community-based vector control has now been developedin the country, focusing particularly on schoolchildren. In Myanmar, prevention and controlmeasures have been focused mainly onsource reduction measures by activecommunity participation and intersectoralcoordination with the education sector forprevention and control in primary schools.Local NGOs have also actively participated.

In the wake of the increasing incidenceof DHF and its geographic spread, it isdesirable to organize national dengue controlprogrammes in each country within theframework outlined below with modificationsas needed for the local situation.

11.3 Planning a Dengue ControlProgramme

A dengue control programme is aimed atreducing morbidity and mortality due to DHF.In the absence of a safe, effective andeconomic vaccine against DF/DHF, vectorcontrol is the only method available to preventand control the disease.

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Source reduction (elimination of Ae.aegypti larval habitats) through communityparticipation is the most promising method fora sustainable, long-term control programme,and is the fundamental control strategy of DF/DHF. However, it is realized that full participa-tion of communities will require considerabletime, since it is based on behavioural change.Meanwhile, outbreaks of DHF accompaniedby deaths continue to occur in manycountries. Therefore, emergency preparednessplans to prevent and control DHF epidemicsshould also be developed, especially in high-risk areas. The planning of DF/DHF controlprogrammes requires the collection andevaluation of basic epidemio-logical,entomological and other relevant informationto determine which control measures shouldbe combined in an integrated manner for thesuccess of the programme. The desired goalmust first be clearly defined. The informationcollected should be analysed for theformulation of a sound and feasible controlstrategy which will best meet the localconditions, needs and resources.

Preparatory phaseVarious basic data to be collected include thoseon metereology, geography, epidemiology andentomology. Data are also required on thesociocultural characteristics of communities aswell as on the feasibility and extent ofcommunity participation, intersectoral action,degree of awareness of the problem in thecommunity, and the community’s expectationsfrom the proposed control programme. Suchdata can be collected through knowledge,attitude and practice (KAP) surveys and otherformative research.

Planning phase

Based upon basic data and epidemiologicalinformation collected in target areas, aworking plan should be prepared oncefeasibility is confirmed. The plan of actionshould be formulated in the light ofadministrative support from variousdepartments and agencies. An intersectoralcommittee should be established to developa collaborative plan and formulate policy,defining objectives, targets, budgeting,logistics, technical guidance, evaluation,training, intersectoral linkages, etc. The itemslisted below should be clearly mentioned inthe plan of action.

ObjectivesThe main purpose and desired goals of thecontrol programme should be defined.

Targets

The degree of desired outcomes of theprogramme with reference to a time lineshould be determined. Each country shouldset up its own targets according to itsepidemiological situation, available manpowerand financial resources.

Strategy

The intervention methods to achieve the goalsand targets of the programme should beoutlined. Area prioritization should beincluded in order to emphasize high-riskareas. Such prioritization of areas should bereviewed periodically to ensure that thelimited resources are effectively allocated.Case management should be emphasized inall areas, but especially in those with high


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mortality. Control measures should be focusedon source reduction by community partici-pation. Decentralization down to local healthservices and intersectoral coordination shouldbe introduced to the control programmes inorder to sustain vector control activities.

Activity Plan

Details of activities to support the strategy,including responsible organizations/agenciesand timeframe, should be defined (Table 7).

Logistic support

Routine requirements for DF/DHF controlshould be estimated and calculated based onthe past experience of the country concerned.Additional requirements for unexpected oremergency requirements of supplies,equipment and insecticides should be plannedfor well in advance. The WHO TechnicalAdvisory Committee has recommended thefollowing items for treating a town covering a20 sq km area during an emergency:

Table 7. Plan of action for the control of dengue fever/dengue haemorrhagic fever vectors

Controlmethod Agent Activities Ways and means

of approach

Source: Bang and Tonn 1993 – Vector Control and Intervention Regional Publication: SEARO No.22 (51)

Government 1. Disposal of refuse2. Provision of reliable

piped water3. Legislation4. Monitoring and

assessment

1. Set up core workingcommittee for inter-and intrasectoralcoordination

Larvalcontrol

Community 1. Larviciding2. Release of larvivorous

fish/copepods

Same as for sourcereduction

Same as for sourcereduction

Government 1. Supply of controlmaterials (larvicides,copepods, fish) andequipment as needed

Sourcereduction

Community 1. Removal/reduction ofnon-essential watercontainers receptive tomosquito breeding

2. Protection of watercontainers from larvalbreeding

1. Health education2. Mass media (radio,

TV, films)3. School children/

housewives4. Volunteers5. PHC workers6. Community leaders

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– technical malathion – 1000 litres (fortwo applications),

– one vehicle-mounted aerosolgenerator, and

– five mist blowers and ten swing fogs.The total number of DHF/DSS cases

should be estimated and essential supplies,equipment and beds needed for casemanagement should be obtained. Diseasesurveillance and information systems shouldbe established and strengthened for earlydetection of DHF/DSS, for early referral tohospitals, and for effective transmissioncontrol. Intensive care units in children’shospitals should develop contingency plans toaccommodate an increased patient load,including diagnostic facilities, drugs and otherrequirements. Development of IEC materialsshould be considered a priority for allocationto high-risk areas.

Implementation phase

After basic information has been collected andworking plans drawn up for each task, a planshould be developed for the efficientoperation of the programme. The programmeshould then be formally inaugurated by theleaders of the concerned villages/towns withthe participation of community leaders from

different localities. These prominent citizensshould appeal to the public to accept theprogramme in the interest of their families,and to extend their full cooperation for itssuccess. The function should be widelypublicized by the mass media.

In a community-based programme, it isimportant to give feedback to the communityabout the successes, failures, and benefits ofthe programme. Such feedback helps inretaining continued support fromcommunities, and thus in sustaining theprogramme, as experienced in Singapore.

Monitoring and evaluation

The plan should include (a) periodicoperational assessments to determine theprogress of work and actual inputs receivedby the programme in terms of materials andmanpower, and (b) periodic entomologicalassessments to determine the success orfailure of the control measures applied to thevector population and/or epidemiologicalanalysis. When the bulk of the work is beingcarried out through community participation,it is desirable to have a built-in mechanism tocross check the work.

Emergency Preperednessand Effective Response

12.1 Predictive IndicatorsDespite ongoing control programmes in somecountries of the Region, dengue epidemics arebeing reported with ever-increasing frequencyand greater numbers of DHF cases. There istherefore an urgent need to establish an early-warning, predictive capability of epidemictransmission, and a rapid emergency responsecapability to contain outbreaks.

Prediction of impending epidemics

Identification of high-risk areas has beendescribed in Chapter 2. The ability to predictan impending epidemic depends on thefollowing factors.

Receptivity for dengue epidemic

Geographical reconnaissance of towns andcities should be carried out to identify andmap all permanent foci of Aedes breeding.The maps should be updated each yearbefore the rainy season.

Vulnerability of the areaAll places where people congregate, which actas centres of transmission, should be identifiedand the pattern of both intra and inter-citymovements of the human population shouldbe determined.

Active surveillance

Active surveillance of suspected, probable andconfirmed cases of DF/DHF should bemaintained as described in Chapter 6. Thelocation of cases by number and serotypesshould be actively monitored. Other cities andcountries in the region should also bemonitored, with regular exchange ofsurveillance data among public healthcounterparts. Sentinel hospitals, clinics andphysicians, and fever-alert surveillance systemsshould be implemented to provide currentdata on the location of virus serotypes and theseverity of illness in the catchment areas. Theobjective is to detect, without delay, theintroduction of a new strain or serotype of

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dengue virus or to detect any unusual increasein the spread of dengue transmission (seesection on Surveillance).

Routine monitoring of DF/DHF cases

The most effective method of predicting aDHF epidemic is the active monitoring ofDF/DHF cases on a weekly basis in thecommu-nity. In addit ion to seasonaltransmission patterns and the number ofreported cases, the disease sever i ty,seroposit ivity rate, virus serotype andgeographic clustering of cases can provideearly warning information on which theprediction of epidemic activity can bebased. This can be done at the health-centre level. Impending epidemics can bedetected by comparing the DHF cases of agiven month/fortnight/week with eitherthose of the same period of the previousyear (last month, fortnight, week) or withthe average number of cases during thatmonth over the last 3-5 years.

12.2 DF/DHF EpidemicManagement

DF/DHF outbreaks can cause high morbidityand mortality in a short span of time, and maycreate panic among the people who expecturgent action from the government. At suchtimes it becomes essential to have a rapid,emergency response plan and to haveadministrative flexibility at the central,provincial and local government levels(63). Sucha response requires the setting of priorities forthe control of DF/DHF/DSS epidemics.

Administrative actions

Emergency Action Committee (EAC)and Rapid Action Team (RAT)

For contingency planning of DHF epidemiccontrol, it is essential that a mechanism isembodied at national, state and local levels forcreation of a multidisciplinary Emergency ActionCommittee (EAC) and a Rapid Action Team(RAT). The EAC is entrusted with alladministrative actions and coordinates allactivities aimed at emergency interventions. TheRAT undertakes epidemiological investigationsand control measures(62,63) (see Annex XIII).

Establishment of emergency controlcentres

Emergency control centres are under theadministrative control of a technical managerappointed by the EAC. The control centremonitors the progress of the epidemic on a24-hour basis throughout the emergency.

Declaration of dengue as a notifiabledisease

DF/DHF should be made a notifiable diseaseto ensure that individual medical practitioners,clinics and hospitals report all suspected casesto the government. This facilitates theidentification and appropriate management ofcases in hospitals, and ensures that measuresare taken to keep hospitals free of Ae. aegypti.

Reporting system

l Peripheral health units should report tothe District/Municipal Health Officer.

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l Confirmation of the epidemic is made bythe Chief, MOD/DOH.

l Reports should be made to the ChiefAdministrator of the District/MunicipalCorporation.

l Reports should be made to the provincialand national level.

Activities

Contingency plans require the following:l Delimitation of epidemic areas.l Mobilization of adequate human and

financial resources, materials andequipment.

l Intersectoral meeting at district/city levelto inform the local authorities of plans.

l Provision of information to communitiesthrough the mass media.

l Implementation of the action plan forcontrol measures.

Case management

Adequate provision of hospital beds,diagnostic facilities, fluids, drugs, equipmentand other requirements must be ensured.

Vector control

Vector control should be based on:(i) insecticide space spraying, (ii) applicationof larvicides, (iii) source reduction, and(iv) health education to ensure involvement ofcommunities, school children and NGOs.

Intersectoral collaboration

This requires (i) political commitment andfinancing, (ii) constitution of intersectoralcommittees for joint activities, and

(iii) maximizing the use of the mass media forhealth education and urgent implementationof plans by communities, school children andNGOs.

Role and functions of publicinformation, media and community

Public information

Public information is vital to allay the fears ofthe community when an epidemic occurs.Public information, therefore, should beexhaustive and clear and should explain howthe disease is caused, how it spreads, how itis controlled, the responsibility of the citizensof the community, and where to gettreatment. Comprehensive communicationguidelines on the treatment and control ofdengue epidemics, including the “Do’s andDon’ts” should be developed to inform thepublic. This includes information generated byother sources.

Role of the media

It is acknowledged that the media can playan important role in epidemic prevention andcontrol. To be effective, the media should begiven accurate information quickly andcomprehensively. Such information should beprovided only through an authorized mediaspokesperson of the Ministry of Health or viathe municipal/district health officer. TheMinistry of Health should provide addressesof authorized information outlets to ensure thereliability of information. It is important toprovide consistent messages. Press releases arethe recommended means of communication.


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Community participation

The prevention and control of dengueepidemics cannot be achieved without thecooperation and involvement of thecommunity. Health managers mustunderstand the social and cultural beliefs ofthe population regarding dengue fever,including whether they understand the role ofthe mosquito in dengue transmission and thebenefit they perceive from vector control. Anintensive campaign to implement communityparticipation should be initiated as part of theemergency response. In DF/DHF emergencyepidemic control campaigns, members of thecommunity are encouraged to undertakesource reduction measures, such as emptyingwater containers, removing solid wastematerial including used tyres, preventingbreeding in man-made breeding places (e.g.cisterns and wells), and undertaking personalprotection methods (e.g. using mosquito netsand coils, etc.) to prevent mosquito bites.

For the success of any campaign, thecommunity should understand theimportance of DF/DHF and that sustainabilityis enhanced by linking the programme withexisting well-organized programmes and bymobilizing societal forces and organizations,both within and outside the health sector, toinitiate and maintain dengue control activities.Details about community actions duringepidemics are included in Annex XIV.

Management of DF/DHF/DSS andlaboratory services in hospitalsduring epidemics

Appointment of coordination committee

During an epidemic of DHF there will be alarge number of patients with DF. As an

epidemic becomes known to the public, largenumbers of patients, both dengue and non-dengue, may overwhelm outpatient andinpatient facilities, rapidly exhausting themedical care staff. It is essential, therefore, toestablish a coordination committee within thehospital to facilitate interdisciplinary andinteragency communication.

Outpatient medical services – specialDHF OPD

Since the prognosis of DHF depends on earlydiagnosis and proper management, and sinceduring the early febrile phase DHF resemblesDF and numerous other viral, bacterial andparasitic infections, patients with high feverand a positive tourniquet test should besuspected of having DHF. They should betested for thrombocytopenia and plasmaleakage which are constant findings in DHF.A CBC with platelet count and haematocritshould be done in the hospital outpatientdepartment or clinic. Since only about one-third of DHF patients will develop shock andthe critical period is reached about the timeof defervesence, patients who are suspectedto have DHF can stay at home during thefebrile phase, with regular follow up every 24hours to monitor whether there is significantleakage of plasma. Patients who live far awayfrom hospitals or whose parents or relativescannot be relied upon to observe clinicalchanges, should be kept for observation asoutpatients. An observation unit ofapproximately 10-20 beds should be set upto accommodate these patients. Dengue feverand some mild cases of DHF can be treatedat outpatient departments and clinics. Thisobservation unit will help to avoid


91

overcrowding of hospital wards and ensurethat persons who have DHF and genuinelyrequire hospital care are admitted. It isessential that the observation unit is wellstaffed and that it has clinical laboratorycapability (see below).

Inpatient services – special DHFtreatment unit

A special DHF treatment unit should beestablished for providing care to DHF/DSSpatients. Those in shock require intensivenursing and medical care, and the unit shouldbe staffed with well-trained nurses. Thereshould be about 20-30 beds with adequateequipment and supplies needed for takingcare of DSS patients. Paramedical workers orparents can assist by giving oral fluid therapyor by monitoring the rate of intravenousadministration and the general status of thepatient.

Clinical laboratory support

Laboratory studies necessary for clinicaldiagnosis include total white blood count,

platelet count and haematocrit determi-nation. The ability to conduct these laboratorytests should be available at outpatientdepartments at all times. A microcentrifuge forhaematocrit determination and a microscopefor platelet estimation should be available atall institutions providing care to DHF patients.

Equipment and medications

A blood pressure manometer with differentsizes of arm cuffs for children in different agegroups is required for tourniquet testing andblood pressure measurements. It is estimatedthat about 20-30% of DHF patients willprogress to shock, that about half of the gradeI-II patients will require intravenous therapywith isotonic salt solution, and that about 10%of the patients may require blood transfusion.Based on these assumptions, the estimates inBox 24 can be made for materials needed.

Training

(a) Hospital staff, doctors and nurses shouldbe trained (short course/seminar) to diagnosecases of DHF, to recognize shock, and to

Box 24Estimated DF/DHF materials required in hospitals

100 cases of DHF – 200-300 litres of normal saline or Ringers acetate solution.

30 cases with shock – 30 litres of volume expander, e.g. Dextran 40 or plasma.

10 cases of DHF – Approximately 10-20 units of fresh whole blood. with significant Oral electrolyte solution as used in diarrhoea. haemorrhage Solutions for volume replacement: 5% dextrose in

normal saline, 5% dextran in 1/2 normal saline.Ringer’s lactate or acetate, plasma expander, Dextran 40.


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provide proper management using WHOcriteria and guidelines.(b) Laboratory workers should be trained todo haematocrits, CBCs and platelet counts orestimation by examination of peripheral bloodsmears and coagulogramme. They should alsobe trained to collect blood specimens forserological diagnosis and/or virus isolation.

Prevention of death

Prevention of death can be achieved by earlydiagnosis, hospital admission, good nursingcare and proper case management. Since onlyabout one-third of DHF cases develop shock,the parents or attendants of patients shouldbe given thorough instructions for taking careof the patient at home during the febrile phaseand to recognize the early warning signs ofshock.

Management of dengue haemorrhagicfever

The major pathophysiologic hallmarks thatdistinguish DHF from DF and other diseasesare abnormal haemostasis and increasedvascular permeability that leads to leakage ofplasma. The clinical features of DHF are ratherstereotypical, with the acute onset of highfever, haemorrhagic diathesis (most frequentlyon the skin), and circulatory disturbance (inthe most severe form as dengue shocksyndrome). Hepatomegaly is usually present,but not always. Thrombocytopenia andconcurrent haemoconcentration, whichrepresent abnormal haemostasis and plasmaleakage respectively, are constant findings. Itis thus possible to make an early and accurate

clinical diagnosis of DHF before the criticalstage of shock occurs.

The management of DHF is entirelysupportive and symptomatic and is directedtowards the replacement of plasma losses.Survival depends on early clinical recognitionand frequent monitoring of patients for plasmaleakage. Early volume replacement when thehaematocrit rises can prevent shock and/ormodify disease severity. In shock cases,satisfactory results have been obtained withthe regimen described in Box 25.

At the Children’s Hospital in Thailand, (64)

where a large number of DHF cases aretreated every year, this regimen (without usingsteroids or vasopressors) has resulted in asteady decline in the case fatality rate of shockcases, from about 5% in 1971 to 2% in 1984and to 0.2% in 1991. The results of studies

Box 25Recommended regimen for

shock cases of DHF

l Immediately and rapidly replace theplasma loss with isotonic salt solutionand plasma or plasma expander (incases of profound shock).

l Continue to replace further plasmalosses to maintain effective circula-tion for a period of 24-48 hours.

l Correct metabolic and electrolytedisturbances (metabolic acidosis,hyponatraemia, hypoglycaemia orhypocalcaemia).

l Give blood transfusion in cases withsignificant bleeding.


93

from various places on the use ofcorticosteroids in treating DSS showed nobenefit, either in reducing the fatality rate, orreducing the volume or duration of fluidtherapy.

Vector control for containment ofepidemics

Development of emergency vectorcontrol programmes

DF/DHF outbreaks often evolve quickly,requiring emergency actions to immediatelycontrol infected mosquitoes in order tointerrupt or reduce transmission and to reduceor eliminate the breeding sites of Ae. aegypti.In order to meet such emergencies, it isessential that persons at all levels, includingindividuals, the family, the community and thegovernment, contribute to preventing thespread of the epidemic. In the followingsections, an attempt is made to highlightemergency actions that can be taken toprevent or contain an incipient epidemic.

Self-reliance actions for vector controland personal protection

At household level

l Kill adult mosquitoes by making use ofcommercially-available safe aerosols(pyrethroid-based). Spray bedroomsincluding c losets , bathrooms andkitchens for a few seconds and closethe rooms for 15-20 minutes. Thetiming of spray should coincide with thepeak biting times of early morning orlate afternoon.

l Intensify efforts to reduce actual orpotential larva habitats.

l Cover water containers in the house toprevent fresh egg-laying.

l Have infants sleep under bed nets duringthe day.

l Wear protective clothing, preferablysprayed with a repellent.

l Use commonly-available repellents duringthe day time and also make liberal use ofmats and coils, etc. during night and day(including all family members – whetherthey stay at home or go to work).

At school level

School children should be provided withhealth education on all aspects of denguefever, i.e. what it is, how it spreads, the roleof mosquitoes, how they breed, and how theycan be controlled. Following health education,school children should be trained on how todetect and eliminate the breeding of Ae.aegypti in and around schools, in their homesand in the neighbourhood.

At community level

At the community level, people should formgroups to supplement and reinforce efforts atthe household level. Such groups can identifycommercial activities such as traders dealingin used tyres, which may be contributing larvalhabitats for the vector. They can createawareness about dengue and seekcooperation for the removal of breedingplaces (see also Annex XIV).

Action by local health authorities

For the control of epidemics, chemical controlof the adult mosquito vector is considered an


94

important strategy in an attempt to interruptor reduce transmission. It should beemphasized, however, that rapid and effectivesource reduction will achieve the same results.Moreover, larval control is more economicaland provides sustainable control by elimina-ting the source of newly-emergent adultmosquitoes. Under most conditions, chemicalspace sprays are not effective and it is rare thatan epidemic will be controlled using thesemethods. Because of their visibility, however,people think the government is doingsomething. This often creates a false sense ofsecurity and prevents the implementation ofthe community as well as the individual effortsoutlined above(53).

There are two main methods of spacespraying for adult mosquito control: (i) coldaerosol ULV, and (ii) thermal fogging. Theguidelines for space spraying with adulticides,and equipment which has been experi-mentally shown to be effective in the controlof caged adult mosquitoes, are included inAnnexes VII and VIII.

12.3 Post-DHF EpidemicManagement

The evaluation of prevention and controlmeasures implemented during an epidemic

are an important learning tool to improveeffectiveness during subsequent epidemics. Aretrospective study of an outbreak providesessential material for case studies as well asfor teaching purposes.

Retrospective study of epidemics –lessons learned

A retrospective study should cover all aspectsof hospital care and case management, anyvariation in clinical signs and symptoms fromthe known management successes, and alladministrative aspects relative to theadequacy of hospital management to meetsuch emergencies. The evaluation studyshould cover all aspects of the agent-host-vector interaction and all morbidity andmortality data including prevalence of theinfection by age, sex, occupation andsociocultural factors which may havepromoted outbreaks, vector prevalence, typesof containers promoting breeding, evaluationof all Ae.aegypti control measures, factorsrelated to cost-effectiveness and sustainability,degree of community participation, degree ofgovernmental preparedness to respond toand control such epidemics, and all otherfactors which will enhance the futurecapabilities of all those involved in epidemiccontrol.

WHO Support ActivitiesThe WHO Regional Office for South-East Asia(SEARO) is committed to:l Together with Member States, continue

to support implementation of the regionalstrategy for the prevention and control ofDF/DHF.

l Cooperate with Member States tocoordinate and strengthen surveillanceactivities on a regular basis, in order toanalyse trends, provide feedback toMember States, and exchangeinformation.

l Lay special emphasis to support countries’efforts in selective, effective, stratified andintegrated vector control with communityand intersectoral participation.

l The establishment of emergencypreparedness capacity to control dengueepidemics and development ofcontingency plans for vector control,including timely hospitalization of DHFcases, education and adequate logistics.

l Provide a Regional Rapid Response Teamto cooperate with Member States in theemergency management of DHF asrequested or required by countries.

l Provide continued support to thedevelopment of training modules,guidelines and other training/educational

materials for case management of DF/DHF/DSS including audio/video materialson the prevention and control of DF/DHF/DSS.

l Facilitate the organization of workshopsand seminars on vector control, laboratorydiagnosis, production of diagnosticreagents, and clinical case managementof DF/DHF/DSS.

l Together with WHO collaborating centresand national reference laboratories,support the establishment of a surveillancenetwork in the Region.

l Continue to support basic research tounderstand the epidemiologicalcomplexities of the disease andoperational research to develop cost-effective control strategies.

l Make an inventory of dengue virusesisolated from DF/DHF cases in eachcountry and coordinate genotypingstudies at WHO collaborating centres.

l Continue to support the development andfield testing of live attenuated tetravalentdengue vaccine at the Mahidol University,Bangkok, Thailand, and futureimplementation of this vaccine for massvaccination in dengue-endemic countriesin the South-East Asia Region.

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Annex IList of National Programmes and

WHO Collaborating Centres

Institutions

Bangladesh

l Malaria and Other Parasitic Control,Directorate-General of Health Services,Mohakhali, Dhaka,BangladeshTel. (8802)606326 Fax (8802)863247

l Institute of Epidemiology, Disease Control and Research,Directorate-General of Health Services,Dhaka, Bangladesh

Bhutanl National Malaria Control Programme,

Gaylegphu, BhutanTel. (975)-3-51115

Indial Director, National Malaria Eradication

Programme22 Sham Nath Marg,Delhi 110052Tel. (91-11)2918576, 2927108Fax 2518329

l Director, National Institute of Communicable Diseases22 Sham Nath Marg,Delhi 110052Tel. (91-11)2913148

Indonesial Directorate of Vector Borne Disease

ControlDirectorate General of Communicable Disease ControlMinistry of Health and Environmental Health, Jl. Percetakan Negara No.29Jakarta, IndonesiaTel. 4247573Fax 62-21 424 7573

Maldivesl Programme Manager

Department of Public Health, MaleRepublic of MaldivesTel. 322488 Fax 314653

Myanmarl Vector Borne Disease Control

Division of Control of Communicable Diseases, Department of HealthMinistry of Health,Yangon, Myanmar

Nepall Epidemiology and Disease Control

Division,Department of Health Services,Teku, Panchali,KathmanduTel. 227268

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102

Sri Lanka

l Epidemiology Unit, Department of Health, Ministry of HealthColomboSri LankaTel. (00-94-1)501110

l Director, Anti Malaria CampaignP.O. Box 1472, Colombo 5Sri LankaTel. (00-94-1)581918

l Medical Research InstituteColombo 8Sri LankaTel. (00-94-1)693532, Fax 691495

Thailand

l Division of General Communicable Disease Control, Department of Communicable Disease ControlMinistry of Public HealthSoi Bamrajnaradul, Tivanond RoadNonthaburi 11000ThailandTel. (66-2)9659182, 5903160-1Fax (66-2)5918432

WHO Collaborating Centres

SEARO

India

l National Institute of Virology (NIV)20-A Dr Ambedkar RoadP.O. Box 11, 411001PoonaFax (+91-212) 622669

l Vector Control Research Centre (VCRC)PondicherryTel. (91-413)72784, 72396Fax (91-413)72422, 72041

Indonesial Vector Control Research Station

Health Ecology Research CentreNational Institute for Health Research and DevelopmentSalatiga, SemarangIndonesiaTel. (0298)27096, Fax (0298)22604

l U.S. Naval Medical Research Unit No.2NAMRU-2 Laboratory, Kotak Pos 226Jakarta Pusat 10570Fax (+62)21 4244507

Thailand

l Queen Sirikit’s National Institute of Child Health, 420/8 Rajvithi RoadBangkok, 10400ThailandFax (+66-2) 2457580

WPRO

Australia

l Queensland University of Technology2 George Street, GPO Box 2434Brisbane Queensland 4001Fax (+61)7 8641534

Japan

l Institute of Tropical MedicineDepartment of VirologyNagasaki University12-4 Sakamoto-Machi852 NagasakiFax (+81)958 476607

Malaysia

l Department of Medical MicrobiologyUniversity of Malaya,59100 Kuala LumpurFax (+60)3 7557740

Annexes

103

Australial University of Western Australia

Queen Elizabeth II Medical CentreNedlandsWestern Australia 6090Fax (+61) 7 33654620

Other RegionsBrazill Instituto Evandro Chagas

c/o Fundacao SESPCaixo Postal 1530BelemFax (+55) 91 2661284

Canadal Laboratory Center for

Disease ControlHealth Protection BranchTunney’s PastureOttawa, Ontario, K1A 0L2Fax (+1)613 9540207

Finlandl Department of Virology

Haartman InstituteUniversity of HelsinkiP.O. Box 21HelsinkiFax (+358)0 94346491

Francel Centre National de

Reference pour les Fievres Hemorragiques et lesArbovirus, Institut Pasteur25 rue du Dr Roux75724 ParisCedex 15Fax (+33)1 40613151

Italyl Laboratory of Virology

Arbovirus UnitIstituto Superiore de Sanita299 Viale Regina Elena00161 RomeFax (+39)6 49902082

Netherlands

l Department of VirologyErasmus University RotterdamP.O. Box 17383000 DR RotterdamFax (+31)10 4365145

Russian Federation

l Ivanovsky Institute of VirologyDepartment of Arboviruses16 Gamaleya Street123098 MoscowFax (+7)095 1907485

United Kingdoml Division of Pathology

Public Health Laboratory ServiceCentre for Applied Microbiology and ResearchPorton Down, SalisburyWiltshire SP4 0JGEnglandFax (+44)1980 612731

USAl Division of Vector-borne Infectious

DiseasesCenters for Disease Control and PreventionP.O. Box 2087Fort CollinsCO 80522Fax (+1)303 2216428


104

l Department of Epidemiology and Public HealthYale University School of Medicine60 College StreetP.O. Box 208034New Haven, CT 06520-8034Fax (+1)203 7854782

l Special Pathogens BranchDivision of Viral and Rickettsial DiseasesNational Center for Infectious Diseases

l Centers for Disease Control and Prevention1600 Clifton Road NEAtlanta, GA 30333Fax (+1)404 6391118

l Center for Tropical DiseasesUniversity of Texas Medical Branch,GalvestonTX 77555-0609Fax (+1)409 7472429

Annexes

105

Annex IIArbovirus Laboratory Request Form

Name of patient _____________________________________ Hospital No. ______________________Address _____________________________________________ Hospital _______________________________________ Age _____________ Sex _________________ Physician _________________________

Date of admission ____________________________ Admission complaint ________________________Date of onset ________________________________

Instructions: Fill the form completely with all clinical findings in duplicate. Saturate the filter-paper discs completely so that the reverse side is saturated and clip them to the form. Obtainadmission and discharge specimens from all patients. If the patient does not return for aconvalescent sample, mail promptly.

Source: Dengue Haemorrhagic Fever: Diagnosis, treatment, prevention and control, second edition, WHO, Geneva, 1995.

Clinical findings: 1. Fever __________________ 0C or 0F (max). Duration ______ days2. Tourniquet test ____________ Petechiae _______________ Epistaxis _________________

Haematemesis/melaena ______________ Other bleeding (describe) __________________3. Hepatomegaly _________________ (cm at right costal margin). Tenderness ___________4. Shock _____________ blood pressure _________ (mmHg) Pulse ________ (per min.)

Restlessness/Lethargy __________ Coldness of extremities/body ___________________

Clinical laboratory findings:

Platelets (X103 ) ____________________/mm3 (on ____________________ day of illness).Haematocrit (%) ____________________ (max) _________________________ (min)

Blood specimens(Acute)Hospital admission Hospital discharge ConvalescentDate____________ Date___________ Date_____________


106

Annex IIIRelative Sensitivity and Interpretation of

Serological Tests

(1) Haemagglutination Inhibition (HI)

l Ideal for seroepidemiology; sensitive; easyto perform; minimal equipment; reliable;best for most flaviviruses, well-standardized.

l Remove non-specific inhibitors andagglutinins from serum; lack of specificity

of serotypes; usually paired serumsamples.

(2) Complement Fixation (CF)

l More specificl More difficult, longer, less widely used;

requires highly-trained personnel.

Interpretation of Dengue Haemagglutination-Inhibition Antibody Responsea

ConvalescentAntibody response S1-S2 Titrec Convalescent titrec Interpretation

intervalb <<1

>4-fold rise >7 days <1:1280 Acute flavivirusinfection, primary

>4-fold rise Any >1:2560 Acute flavivirusspecimen infection, secondary

>4-fold rise >7 days <1:1280 Acute flavivirusinfection, eitherprimary or secondary

No change Any >1:2560 Recent flavivirusSpecimen infection, secondary

No change >7 days <1:1280 Not dengueNo change <7 days <1:1280 UninterpretableUnknown Single <1:1280 Uninterpretable

specimen

Clarke OH, Casals J. -American Journal of Tropical Medicine and Hygiene, 1958, 7:561-573.(a) These criteria were derived empirically from data accumulated at the US Armed Forces Research Institute of Medical

Sciences, Bangkok, Thailand. Individual laboratories should assess the sensitivity of their assay with standard serafrom WHO collaborating centres. Laboratories should also establish baseline data for the population they serveduring a period of little or no flavivirus transmission. Test results should be transformed to reduce variance. Resultsthat are two standard deviations greater than the geometric mean may be presumed to indicate recent dengueinfection.

(b) Interval in days between acute (S1) and convalescent (S2) specimens.(c) Against any dengue antigen.

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(3) Neutralization Test (NT)

l Most specific and sensitive; mostly usedPRNT

l Detects past infectionl Expensive and time-consuming

(4) IgM-capture (Mac-ELISA)

l New, simple, RAPID, IgM, only one sampleneeded, screening many samples.

l Less sensitive than HI

(5) IgG-EIA (Indirect IgG ELISA)

l Insensitive

(6) Dot Blot Immunoassay

l Reagents and test procedures areevolving

l Needs standardization

Interpretation of MAC-ELIZA Resultsa

IgM antibody S1-S2 IgM to Interpretationc,d

response intervalb IgG ratio

Increase in molar 2-14 days High Acute flavivirus infection,fraction primary

Low Acute flavivirus infection,secondary

Elevated, no change 2-14 days High Recent flavivirus infection,or decrease in primarymolar fraction

Low Recent flavivirus infection,secondary

Elevated Single High Recent flavivirus infection,specimen primary

Low Recent flavivirus infection,secondary

(a) These criteria were derived empirically from the data accumulated at the US Armed Forces Research Institute ofMedical Sciences, Bangkok, Thailand. Individual laboratories should assess the sensitivity of their assay withstandard sera from WHO collaborating centres. Test results should be transformed to reduce variance. Resultsthat are two standard deviations greater than the geometric mean may be presumed to indicate elevated levelsof anti-dengue IgM or IgG.

(b) Guidelines do not apply to intervals between acute (S1) and convalescent (S2) specimens greater than 14 days.(c) In order to infer whether the dengue virus elicited anti-flavivirus IgM, laboratories must test with a regionally

appropriate panel of flavivirus antigens. Laboratories must also determine appropriate criteria for categorizingprimary and secondary sero responses.

(d) Sera for standardization of the assay are available from the Chief, Department of Virology, US Armed ForcesResearch Institute of Medical Sciences, 315/6 Rajvithi Road, Bangkok 10400, Thailand (fax 66-2-247-6030).

Source: Management of Dengue Epidemic, WHO/SEARO, May, 1997


108

Annex IVSample Size in Aedes Larval Surveys

For Aedes larval surveys, the number of housesto be inspected in each locality depends onthe level of precision required, level ofinfestation, and available resources. Althoughincreasing the number of houses inspectedleads to greater precision, it is usuallyimpractical to inspect a large percentage ofhouses because of limited human resources.

Table 1 shows the number of houses thatshould be inspected to detect the presenceor absence of infestation. For example, in alocality with 5,000 houses, in order to detectan infestation of >1%, it is necessary toinspect at least 290 houses. There is still a 5%chance of not finding any positive houseswhen the true house index = 1%.

Table 2 shows the number of houses thatshould be inspected in a large (>5 000houses) positive locality, as determined by theexpected house index and the degree ofprecision desired. For example, if thepreliminary sampling has indicated that the


100 200 300 1,000

2 0.2-7.0 0.5-5.0 0.7-4.3 1.2-3.1 5 2-11 2-9 3-8 4-710 5-18 6-14 7-14 8-1220 13-29 16-26 16-25 18-2350 40-60 43-57 44-56 47-5370 60-79 62-76 64-75 67-73

Table 2. Precision of the Aedes houseindex in large localities (>5,000 houses)

95% confidence interval of the house indexHouse

index (%)

Table 1. Number of houses thatshould be inspected to detect

Aedes larval infestation

True house indexNumber of houses

in the locality

>1% >2% >5%

100200300400500

1,0002,0005,000

10,000Infinite

95155189211225258277290294299

78105117124129138143147148149

45515455565758595959

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expected house index is approximately 10%,and a 95% confidence interval of 8%-12% isdesired, then 1,000 houses should beinspected. If there are only sufficient resourcesto inspect 200 houses, the 95% confidencelimits will be 6%-14%. In other words, thereis a 5% chance that the true house index isless than 6% or greater than 14%.

In small localities, the same precision maybe obtained by inspecting fewer houses. Forexample, if the expected house index is 50%and a 95% confidence interval of 44%-56%is acceptable, then in a large locality it wouldbe necessary to inspect 300 houses (Table 2).However, as seen in Table 3, if the localityconsists of only 1,000 houses, the sameprecision will be obtained by inspecting 231houses.

Table 3. Number of houses to inspectin small localities

100 200 300 1,000

50 33 40 50 50100 50 66 75 100200 67 100 120 170300 77 122 150 230400 80 134 171 290500 83 142 189 330

1,000 91 166 231 5005,000 100 200 285 830

10,000 100 200 300 91020,000 100 200 300 95030,000 100 200 300 1,00040,000 100 200 300 1,000

100,000 200 300 1,000

Total numberof houses inthe locality

Number of houses to be inspectedfor desired precision if this were a

large locality (from Table 2)

Source: Scientific Publication No.548, PAHO, 1994


110

Annex VPictorial Key to Aedes (Stegomyia) Mosquitoes in

Domestic Containers in South-East Asia*Adults

Postspiracular setae absent Postspiracular setae present

Aedes albopictusAedes aegypti

Scutum with lyre-shaped white markings

Scutum with a long median longitudinalwhite stripe extending from anteriormargin to about level of wing root

Erect forked scales numerous,not restricted to occiput

Erect forked scales notnumerous, restricted to occiput

Lower mesepimeralsetae present

* Adapted from Yiau-Min Huang. The mosquitoes of Polynesia with a pictorial key to some species associated with filariasis and/or dengue fever.Mosquito Systematics, 1977, 9: 289-322.

Lower mesepimeralsetae absent

Culex quinquefasciatus Say Polynesian feral species Polynesian feral species

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Annex V (contd.)

Larvae

Siphon with 4 pairs of subventral tufts Siphon with a single pair of subventral tufts

Culex quinquefasciatus Say

(1) Comb in a patch of several rows ofscales, those of distal row elongate

and varied in development

(1) Comb in a single row

(1) Mental plate with at least 10 teeth on eachside of median tooth

(1) Ventral brush with 4 or 5 pairs of setae and(2) no precratal tufts

(2) Seta 1-C very slender, filamentous distally,usually very lightly pigmented

Polynesian feral Aedes species


112

Annex V (contd.)

(1) Ventral brush with 5 pairs of setae (1) Ventral brush with 4 pairs of setae

Saddle complete Saddle incomplete(2) Comb scale with very strongdenticles at base of apical spine

Aedes aegypti (Linnaeus)

Seta 4a, b-X single Seta 4a, b-X branched

Aedes albopictus (Skuse) Polynesian feral Aedes species

Polynesian feral Aedes spp.

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Annex VIStandard Design for Mosquito Proofing of

Overhead Tanks and Cisterns

Standard Design for Overhead Tank with Cover Design for Mosquito Proofing ofOverhead Tank/Wells/Cisterns

Source: R.S.Sharma, G.K.Sharma and G.P.S.Dhillon, Epidemiology and control of malaria in India - 1996.Dte. of NMEP, 22 Sham Nath Marg, Delhi 110 054, India

Design for Masonry Chamber and Soak Pit for Sluice Valve and Water Meter

LOCK45 c.m. Dia. COVER

(Slightly Convex)

CHECK NUT

OVERFLOW PIPEPROTECTED WITHMETALLIC PLACEPERFORATIONS NOTEXCEEDING 1.5 m.m.

M.S. OR R.C.C.EXTERNAL SIDE OF TANK

PERFORATIONSNOT EXCEEDING1.5 m.m.

SECTION

SOAK PIT


114

Annex VIIProcedure for Treating Mosquito Nets

and Curtains

The steps described below mainly refer totreatment of mosquito nets with permethrin.The net treatment technique can be easilyused for curtains.

(a) Calculate the area to be treated

Measure the height, length and width of thenet. Assuming a rectangular mosquito net is150 cm high, 200 cm long and 107 cm wide,the calculations are as follows:

Area of one end = 107 x 150= 16,050 cm2

Area of one side = 200 x 150= 30,000 cm2

Area of top = 107 x 200= 21,400 cm2

The s ides and ends need to bemultiplied by 2:2(16,050+30,000) = 92,100+21,400 (end) (side) (top)

= 113,500 cm2

If 10,000 cm2 = 1m2 then113,500/10,000 = 11.35 m2 area of net

(b) Determine how much insecticide isneeded

Assume that a permethrin emulsifiableconcentrate will be used, and the dosagedesired is 0.5 grams per square metre.

To determine the total grams required,multiply the net size by the dosage:

11.35 x 0.5 = 5.67 grams ofinsecticide needed.

(c) Determine the amount of liquidrequired to saturate a net

In order to determine the percentage solutionto be used for dipping, it is first necessary todetermine the approximate amount of waterretained by a net. Another term for dippingis soaking.

Pour five litres of water, but preferably adilute solution of the insecticide to be used,into a plastic pan or other suitable container.For cotton, a 0.3% solution can be tried; forpolyethylene or other synthetic fiber, a 1.5%solution can be tried. Add the net to thesolution till it is thoroughly wet and thenremove it. Allow the drips to fall into a bucketfor 15 to 30 seconds. Set the net aside.Repeat the process with two other nets.Cotton nets can be lightly squeezed but notthe synthetic ones. Measure the water orsolution remaining in the dripping/soakingcontainer and in the bucket to calculate theamount of liquid used per net.

Assuming that one polyethylene netretained 280 ml of solution, the percentage

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concentration required for dipping iscalculated as follows:

grams required per net 5.67---------------------------------------- = --------ml solution retained per net 280

= 2%

(d) Preparation of dipping solutions totreat bulk quantities of mosquitonets or curtains

The general formula is:

X = (A/B) - 1in which X = parts of water to beadded to 1 part of emulsifiableconcentrateA = concentration of the emulsifiableconcentrate (%)B = required concentration of thefinal solution (%)Example: A 2.0% solution of perme-thrin for dipping nylon mosquito netsor curtains is to be prepared from a25% concentrate.

X = (25/2.0) - 1= 12.5 - 1 = 11.5Therefore 11.5 parts of water to 1 partof concentrate are required, or one litreof concentrate to 11.5 litres of water.Example: A 2.0% solution of perme-thrin for dipping nylon mosquito netsor curtains is to be prepared from a50% concentrate.

X = (50/2) - 1 = 24Therefore, 24 parts of water to 1 partof concentrate are required, or one litreof concentrate to 24 litres of water.Example: A 0.3% solution ofpermethrin for dipping cotton

mosquito nets or curtains is to beprepared from a 25% concentrate.

X = (25/.3) - 1= 83.3 - 1 = 82.3

or rounded to 82.Therefore, 82 parts of water to 1 partconcentrate are required, or one litreof concentrate to 82 litres of water, orone-half litre of concentrate to 41litres of water to accommodate asmaller container.Example: A 0.3% solution of perme-thrin for dipping cotton mosquito netsor curtains is to be prepared from a50% concentrate.

X = (50/.3) - 1= 166.6 - 1 = 165.6

or rounded to 166.Therefore, 166 parts of water to 1part of concentrate are required, orone litre of concentrate to 166 litresof water, or one-half litres ofconcentrate to 83 litres of water toaccommodate a smaller container.

(e) Preparation of a 2% dippingsolution using a one-litre bottle of25% or 50% permethrin emulsifi-able concentrate for soakingpolyethylene or other syntheticfiber nets or curtains. This opera-tional approach minimizes detailedmeasurements in the field.

For 25% concentrate:

Add 11.5 litres water to a container (with pre-measured marks to indicate volume)


116

Add 1 litre (1 bottle) concentrate tothe containerTotal volume : 12.5 litresGrams permethrin : 250% concentration : 2%


Add 24 litres water to a containerAdd 1 litre (1 bottle) concentrate tothe containerTotal volume : 25 litresGrams permethrin : 500% concentration : 2%

(f) Preparation of a 0.3% dippingsolution using a one-litre bottle of25% or 50% permethrinemulsifiable concentrate forsoaking cotton nets or curtains


Add 82 litres of water to a containerAdd 1 litre (1 bottle) concentrate tothe containerTotal volume : 83 litresGrams permethrin : 250% concentration : 0.3%


Add 166 litre of water to a containerAdd 1 litre (1 bottle) concentrate tothe containerTotal volume : 167 litresGrams permethrin : 500% concentration : 0.3%

(g) Drying of nets

Polyethylene and synthetic nets are dried ina horizontal position. Do not hang to dry.Drying the nets on mats removed from houseshas proved to be convenient and acceptable.The nets should be turned over about onceevery hour for up to three or four hours. If theweather is good, the nets can be dried outsidein the sun but for not more than several hours.Under rainy conditions, they can be placedunder sheltered areas or inside and leftovernight to dry. When dripping no longeroccurs, they can be hung up to finish drying.Treated cotton nets which are not over-saturated and do not drip can be hung up todry soon after the soaking procedure.

(h) Treatment of one net in a plasticbag (soaking)

As shown in (a) above, if it is assumed thatthe net size is 11.35 m2, 5.67 grams ofpermethrin are needed to achieve a targetdosage of 0.5 grams per square metre, andthis size net absorbs 280 ml of solution.

The amount of 25% permethrin emulsifi-able concentrate to use is determined asfollows:

grams required x 100= 5.67 x 100= 22.68 ml

rounded to 23 ml% concentrated used: 25Therefore, 23 ml of 25% permethrin is

mixed with 280 ml of water. The net is placedinside the bag and the solution added. Thenet and solution are mixed together, shakenand kneaded in the bag. The net is removedand dried on top of the bag or a mat as

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described in (g) above. The amount of watercan be reduced by 23 ml if there is excessrun-off after the net is removed from the bag.

(i) Summary of treatment procedures

The important points in the treatment aresummarized as follows:(1) Dipping is the preferred method of nettreatment. A 2% solution is usually sufficientto achieve a target dosage of 0.5 grams persquare metre of permethrin on polyethylene,polyester, nylon or other type of synthetic fibernet or curtain. The residual effect lasts for sixmonths or more. A 2% solution can be simplyprepared by pouring the contents of a one-litre bottle of 25% permethrin emulsionconcentrate into a container with 11.5 litresof water. With a 50% concentrate, one litreis poured into 24 litres of water. The containerused can be marked to show one or both ofthese volume levels. A 0.3% solution isnormally required for cotton material, whichabsorbs more liquid. Responsible staff need tocheck on the dosage applied and refine theoperation accordingly. With bamboo curtainsor mats used over doors or windows, a higherdosage (1.0 gram per square metre) can beused.(2) Dipping the nets in a permethrin solutionis a fast and simple method for treating nets

and curtains under urban or rural housingconditions. Community members can easilylearn the technique required for follow-uptreatment. A dish-pan type of plastic oraluminium container which holds 15 to 25litres of solution has been found to be quitesuitable. Normally, about one litre of solutioncan treat four to five double (10m2) sizepolyethylene or polyester nets. When the netsare removed from the solution, they shouldbe held to drip in a bucket for no more thanone minute before being laid out to dry in ahorizontal position. Straw mats removed fromhouses are quite suitable for drying the netsoutside in open air. With one dipping station,about 150 nets or curtains can be treated intwo hours or less.(3) About 100 treated double-size nets or anequivalent area of curtain material can protect250 persons. It is not reasonable to expectevery person in a crowded household to sleepunder a net. It is important that every housein a community or village has one or twotreated nets to kill mosquitoes so as to reducethe vector density. When used in this manner,protection is provided to those who do noteven sleep under the nets. Infants and smallchildren can sleep under the nets during daytime.

Source: WHO/Western Pacific Region. Background Document No.16, 1995


118

Annex VIIIQuantities of 1% Temephos (Abate) Sand GranulesRequired to Treat Different-size Water Containers

to Kill Mosquito Larvae

50 5 1100 10 2200 20 4250 25 5500 50 10

1000 100 20

Methoprene (altosid) briquettes can also be used in large water drums or overhead storage tanks. Onebriquette is suitable to treat 284 litres of water. Briquettes of Bacillus thuringiensis H-14 can also beused in large cistern tanks.

Size of water jar, drum orother container in litres

Less than 25

Grams of 1% granulesrequired

Less than 5

Number of teaspoons required,assuming one teaspoon holds 5 grams

Pinch: small amount heldbetween thumb and finger

Source: WHO/Western Pacific Region Background Document No. 16, 1995

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Annex IXProcedure, Timing and Frequency of

Thermal Fogging and ULV Space Spray Operations

l The vehicle is driven at a steady speed of6-8 km/hr (3.5-4.5 mile/hr) along thestreets. Spray production should be turnedoff when the vehicle is stationery.

l When possible, spraying should be carriedout along streets that are at right angles tothe wind direction. Spraying shouldcommence on the downwind side of thetarget area and progressively move upwind.

l In areas where streets run parallel as wellas perpendicular to the wind direction,spraying is only done when the vehicletravels upwind on the road parallel to thewind direction.

l In areas with wide streets with houses andbuildings far from the roadside, the sprayhead should point at an angle to the leftside of the vehicle (in countries wheredriving is on the left side of the road). Thevehicle should be driven close to the edgeof the road.

l In areas where the roads are narrow, andhouses are close to the roadside, the sprayhead should be pointed directly towardsthe back of the vehicle.

l In dead-end roads, the spraying is doneonly when the vehicle is coming out ofthe dead-end, not while going in.

Basic stepsThe steps listed below are to be followed incarrying out the space spraying of adesignated area:l The street maps of the area to be sprayed

must be studied carefully before thespraying operation begins.

l The area covered should be at least 300metres within the radius of the housewhere the dengue case was located.

l Residents should be warned before theoperation so that food is covered, firesextinguished, and pets are moved outtogether with the occupants.

l Ensure proper traffic control whenconducting outdoor thermal fogging sinceit can pose a traffic hazard to motoristsand pedestrians.

l The most essential information about theoperation area is the wind direction.Spraying should always be done fromdownwind to upwind, i.e. going againstthe direction of the wind.

Vehicle-mounted sprayingl Doors and windows of houses and

buildings in the area to be sprayed shouldbe opened.


120

l The spray head should be pointed at a45o angle to the horizontal to achievemaximum throw of droplets.

l Vector mortality increases downwind asmore streets are sprayed upwind inrelation to the target area.

Portable thermal foggingl Thermal fogging with portable thermal

foggers is done from house to house, alwaysfogging from downwind to upwind.

l All windows and doors should be shut forhalf an hour after the fogging to ensuregood penetration of the fog and maximumdestruction of the target mosquitoes.

l In single-storey houses, fogging can bedone from the front door or through anopen window without having to enterevery room of the house. All bedroomdoors should be left open to allowdispersal of the fog throughout the house.

l In multi-storey buildings, fogging is carriedout from upper floors to the ground floor,and from the back of the building to thefront. This ensures that the operator hasgood visibility along his spraying path.

l When fogging outdoors, it is important todirect the fog at all possible mosquitoresting sites, including hedges, covereddrains, bushes, and tree-shaded areas.

l The most effective type of thermal fog formosquito control is a medium/dry fog, i.e.it should just moisten the hand when thehand is passed quickly through the fog ata distance of about 2.5-3.0 metres in frontof the fog tube. Adjust the fog setting sothat oily deposits on the floor and furnitureare reduced.

Back-pack aerosol spraying withULV attachments

Basic points

l Each spray squad consists of fourspraymen and one supervisor.

l Each sprayman sprays for 15-30 minutesand then is relieved by the next sprayman.For reasons of safety, he must not spraywhen tired.

l The supervisor must keep each spraymanin his sight during actual spraying in casehe falls or needs help for any reason.

l Do not directly spray humans, birds oranimals that are in front of spray nozzlesand less than five metres away.

l Spray at full throttle. For example, a ULVFontan nozzle tip 0.4 can deliver 25 mlof malathion per minute, and a 0.5 tip,65 ml. The smaller tip is usually preferredunless spraymen move quickly from houseto house. Some machines can run forabout one hour on a full tank of petrol.

House spraying technique

l Do not enter the house. House sprayingmeans spraying in the vicinity of the house.

l Stand 3-5 metres in front of the house andspray for 10 to 15 seconds, directing thenozzle towards all open doors, windowsand eaves. If appropriate, turn away fromthe house and, standing in the same place,spray the surrounding vegetation for 10to 15 seconds.

l If it is not possible to stand three metresfrom the house due to the closeness ofhouses and lack of space, the spray nozzleshould be directed towards houseopenings, narrow spaces and upwards.

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l While walking from house to house, holdthe nozzle upwards so that particles candrift through the area. Do not point thenozzle towards the ground.

l Spray particles drift through the area andinto houses to kill mosquitoes whichbecome irritated and fly into the particles.The settled deposits can be residual forseveral days to kill mosquitoes restinginside houses and on vegetation notexposed to the rain.

l This technique permits treatment of ahouse with an insecticide ranging from 1to 25 grams in one minute. The dosagedepends on the discharge rate, concen-tration of insecticide applied, and time ittakes to spray the house. For comparison,an indoor residual house spray mayrequire 30 minutes of spraying to deposit300 grams of insecticide. This assumes adosage of two grams per square metre to150 square metres of sprayable surface.

Information to be given to inhabitants

l Time of spraying, for example 0630 to1000 hours.

l All doors and windows should be open.l Dishes, food, fish tanks, and bird cages

should be covered.l Stay away from open doors and windows

during spraying, or temporarily leave thehouse and/or the sprayed area until thespraying is completed.

l Children or adults should not follow thespray squad from house to house.

Timing of applicationSpraying is carried out only when the rightweather conditions are present and usuallyonly at the prescribed time. These conditionsare summarized below:

For optimum sprayingconditions, please notel In the early morning and late evening

hours, the temperature is usually cool.Cool weather is more comfortable forworkers wearing protective clothing. Also,adult Aedes mosquitoes are most activeat these hours.

Most favourable Average Unfavourableconditions conditions conditions

Time Early morning Early to mid-morning Mid-morning to(0630-0830 hrs) or late afternoon, mid-afternoonor late evening early evening

Wind Steady, between 0-3 km/hr Medium to strong,3-13 km/hr over 13 km/hr

Rain No rain Light showers Heavy rain

Temperature Cool Mild Hot


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In the middle of the day, when thetemperature is high, convection currentsfrom the ground will prevent concentrationof the spray close to the ground where adultmosquitoes are flying or resting, thusrendering the spray ineffective.

l An optimum wind speed of between 3and 13 hm/hr enables the spray to moveslowly and steadily over the ground,allowing for maximum exposure ofmosquitoes to the spray. Air movementsof less than 3 km/hr may result in verticalmixing, while winds greater than 13 km/hr disperse the spray too quickly.

l In heavy rain, the spray generated losesits consistency and effectiveness. Whenthe rain is heavy, spraying should stop andthe spray head of the ULV machine shouldbe turned down to prevent water fromentering the blower.

l Spraying is permissible during lightshowers. Also, mosquito activity increaseswhen the relative humidity reaches 90,especially during light showers.

Frequency of applicationThe commencement and frequency ofspraying generally recommended is as follows:l Spraying is started in an area (residential

houses, offices, factories, schools) as soonas possible after a DF/DHF case from thatarea is suspected.

l At least one treatment should be carriedout within each breeding cycle of the

mosquitoes (seven to ten days for Aedes).Therefore, a repeat spraying is carried outwithin seven to ten days after the firstspraying. Also, the extrinsic incubationperiod of dengue virus in the mosquito is8 to 10 days.

Evaluation of epidemic sprayingWithin two days after spraying duringoutbreaks, a parous rate of 10% or less, incomparison to a much higher rate beforespray ing, indicates that most o f themosquito population is newly-emerged andincapable of transmitting the disease. Thisalso indicates the spray was effective andgreatly reduced transmission by killing theolder infected mosquito populat ion.However, a low parous rate after sprayingcan occur in the absence of a markedreduction in vector density. This can beattributed to the emergence of a newpopulation of mosquitoes which escapedthe spray, a relatively low adult densitybefore spraying and adult samplingmethods which show considerablevariations in density in the absence ofcontrol. An effective spray programmeshould also be accompanied by a reductionin hospitalized cases after the incubationperiod of the disease in humans (about5 - 7 days) has elapsed. The spraying shouldbe repeated at seven day intervals toe l iminate the poss ib i l i ty of in fectedmosquitoes.


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Annex XGuidelines For Chemical Space Spraying

Aedes aegypti is the main vector of DF/DHFand has been responsible for all urbanepidemics of this disease. Ae. albopictus is alsoinvolved in dengue transmission, mainly in theSouth-East Asia and the Western PacificRegions. Ae. aegypti has a close associationwith man and it is a highly domestic species,with more than 90% resting on non-sprayablesurfaces in houses. Indoor residual treatmentof houses is therefore not generallyrecommended. Chemical control usinginsecticides generally has very little impact forlong-term control of DF/DHF. Thus use ofinsecticides should be discouraged for long-term prevention and control. However,experiments on the control of Ae. aegypti in

several countries in the Region has shown thatthorough treatment at an interval of 1-2 weekswith portable fogging applicators together withtruck-mounted applicators yielded control ofAe. aegypti. Space spraying with insecticidesshould be considered an epidemiccontingency measure. Total coverage shouldbe targeted for, however attention should befocused inside houses and in places wherehigh vector densities have been recorded.Space spraying should be implemented in acompact community and should be within aradius of 400-500 metres of the affectedhouses.

Suitable insecticides for thermal and coldaerosols are indicated in the table below.


124

Insecticides suitable as cold aerosol sprays and forthermal fogs for mosquito control

Toxicity:Insecticide Chemicala oral LD50of ai.b

for rats(mg/kgbody weight)

Chlorpyrifos OP 10-40 150-200P 135Cyfluthrin PY 1-2 - 500Cypermethrin PY 1-3 - 7180Cyphenothrin PY 2-5 - 2250-2640Deltamethrin PY 0.5-1.0 - >2940c,d

D-phenothrin PY 5-10 - >10,000Etofenprox PY 10-20 10-20 >40,000Fenitrothion OP 250-300 270-300 503Fenthion OP 150 - 330d

Malathion OP 112-693 500-600 >4000Naled OP 56-280 - 430Permethrine PY 5-10 - >4000c,d

Pirimiphos-Methyl OP 230-330 180-200 2018Propoxur C 100 - 95Zeta-Cypermethrin PY 1-3 - 86

a PY = Synthetic pyrethroid, OP = organophosphorus, and C= Carbamateb ai.= active ingredientc Because of their low dermal toxicity and on the basis of experience with their use, these products have been

classified as Class III in the WHO Hazard Classification, Table 5 (WHO/PCS/94.2).d Dermal toxicitye Also used in mixtures with knock-down agents or synergists

Source: WHO (1997), WHO/CTD/WHOPES/97.2

Cold Thermal

Dosage of ai.b (g/ha)

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Annex XISafety Measures For Insecticide Use

Safety measures for insecticide use areadopted to protect the health and lives ofthose applying insecticides. These measuresseek to minimize the degree of poisoning byinsecticides and exposure to insecticides,prevent accidental poisoning, monitor sub-acute poisoning, and provide adequatetreatment for acute poisoning. These mea-sures can be broken down into the four broadcategories listed in the box below.

The human population exposed toinsecticide treatment is of prime importance.It must be ensured that health hazards are nota problem.

1. Choice of insecticides to beused

The choice of an insecticide for vector controlis determined by the following factors:l toxicity and its safety to humans and to

the environment;l effectiveness against the vector, andl cost of the insecticide.

In weighing the relative importance of thethree factors above, the following are impor-tant aspects from a safety standpoint.l An effective and/or cheap insecticide

should not be used if the chemical is highlytoxic to humans and other non-targetorganisms.

l Pyrethroids, generally, have very lowmammalian toxicity when compared toother groups of insecticides such ascarbamates.

l The liquid formulation of an insecticideis usually more dangerous than a solidformulation of the same strength. Certainsolvents in liquid formulation facilitate skinpenetration.

l With regard to occupational exposure,dermal exposure is more important thangastrointestinal or respiratory exposure.

Four Issues forSafety Measures

l the choice of insecticides to beused;

l the safe use of insecticides;

l the monitoring of sub-acuteinsecticide poisoning, and

l the treatment of insecticidepoisoning.


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Thus, an insecticide with low dermaltoxicity is preferred.

l The latest information on the safety aspectof insecticides being considered must beavailable before a wise choice can be made.

2. The safe use of insecticidesThe key to the safe use of insecticides is tocontrol and minimize the level of routine oraccidental exposure of an individual to a giveninsecticide. The level of exposure is in turndependent on many factors, as outlined in thebox below.

In order to minimize the routine andaccidental exposure of staff to insecticides,safety precautions must be observed at allstages of insecticide use.

Safety precautions during storage:

l Store insecticides in containers with theoriginal label. Labels should identify thecontents, nature of the material,preparation methods, and precautions tobe employed.

l Do not transfer insecticides to othercontainers, or to containers used for foodor beverages.

l All insecticide containers must be sealed.l Keep insecticides in a properly-designated

place, away from direct sunlight, food,medicine, clothing, children and animals,and protected from rain and flooding,preferably in a locked room with postedwarning signs such as “Dangerous -Insecticides - Keey Away”.

l To avoid unnecessary and prolongedstorage of insecticides, order onlysufficient amounts needed for a givenoperation, or order on a regular basis (e.g.every three months depending on routineneeds), or order only when stocks aregetting low.

l Stocks received first must be used first.This avoids prolonged storage of any batchof insecticide.

Steps before insecticide use:

l Read the label carefully and understandthe directions for preparing and applyingthe insecticides as well as the precautionslisted, then follow the directions andprecautions exactly.

l Know the first-aid measures and anti-dotes for the insecticides being used.

Level of Exposure Depends on:

l Insecticide storage conditions;

l Personal hygiene and attitude ofworkers;

l Knowledge and understanding ofworkers concerning insecticides;

l Equipment used;

l Method and rate of application;

l Environmental conditions such asprevailing winds, temperature andhumidity;

l Duration of work, and

l Protective clothing and mask used.

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During mixing and spraying/foggingwith insecticides:

l Do not drink, eat or smoke while working.This prevents accidental inhalation oringestion of insecticides.

l Mix insecticides in a well-ventilated area,preferably outdoors.

l Mix only as much insecticide as is neededfor each application. This will reduce theproblem of storing and disposing of excessinsecticide.

l Do not smell or inhale insecticides.l Never mix insecticides directly with bare

hands.l Stand with the wind blowing from behind

when mixing insecticides.l Do not clear blocked spray nozzles by

blowing with the mouth.l Make sure that the spray equipment does

not leak; check all joints regularly.l Keep all unconcerned people away from

where insecticides are being mixed.l Exposure to spraying normally should not

exceed five hours a day.l When spraying is undertaken, the hottest,

most humid period of the day should beavoided if possible. It is best to applyinsecticides early in the morning or latein the evening. This minimizes excessivesweating and encourages the use ofprotective clothing. Also, high temp-eratures increase skin absorption ofinsecticides.

l Those applying insecticides should alwayswear long-sleeved shirts and trousers.

l Wear protective clothing and headgear,where necessary, to protect the main part

of the body, as well as the head and neck,lower legs, hands, mouth, nose and eyes.Depending on the insecticide and typeof application, boots, gloves, goggles andrespirator may be required.

l Mixers and baggers should wear rubberboots, gloves, aprons and masks, sincethey come in contact with technicalmaterial and concentrated formulations.

l Those engaged in thermal fogging andULV spraying should be provided withoveralls, goggles, hats and masks.

l Those engaged in larviciding (e.g. withtemephos) need no special protectiveclothing because the risk of toxicity is low.

l To protect yourself and your family, neverwork with insecticides in your streetclothes.

l Do not wear unwashed protectiveclothing. Make sure your gloves and bootshave been washed inside and outsidebefore you put them on.

l Take heed of the wind direction to avoiddrift.

Steps after spraying/fogging ofinsecticides:

l Wash all spray equipment thoroughly andreturn to the storeroom. It is important tomaintain equipment in good workingorder after usage.

l Empty insecticide containers should notbe used in the household to store food ordrinking water. They should be buried orburned. Larger metal containers shouldbe punctured so that they cannot bereused.


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l Used containers can be rinsed two orthree times with water, scrubbing the sidesthoroughly. If a drum has contained anorganophosphorus compound, an addi-tional rinse should be carried out withwashing soda, 50 g/l (5%), and the solutionallowed to remain in the containerovernight. A soakage pit should beprovided for rinsings.

l All workers must wash thoroughly withsoap and water. This removes deposits ofinsecticides on the skin.

l All protective clothing should be washedafter each use.

l All usages of insecticides must be recorded.l Eat only after a thorough washing with

soap and water.

3. Monitoring sub-acuteinsecticide poisoning

Regular medical surveillance of all spraymenmay be required if space spray operations aredone on a routine, long-term basis.l Mixers, baggers, and spraymen should be

instructed to detect and report any earlysigns and symptoms of mild intoxication.

l Any undue prevalence of illness notassociated with well recognized signs andsymptoms of poisoning by a particularinsecticide should be noted and reported.

l A regular medical examination, includingthe determination of blood cholinesterasefor those applying organophosphoruscompounds, should be conducted. If thelevel of cholinesterase activity decreasessignificantly (50% of a well-establishedpre-exposure value), the affected operatormust be withdrawn from exposure untilhe recovers. Test kits for monitoringcholinesterase activity are available.

Symptoms of insecticide poisoning

Field workers should be taught to recognizethe following symptoms:

DDT and other organochlorinesApprehension, excitement, dizziness, hyper-excitability, disorientation, headache, muscularweakness and convulsions. These compoundsare normally not used for DHF vector control.

Malathion, fenitrothion and otherorganophosphates

Early symptoms include nausea, headache,excessive sweating, blurred vision, lacrimation(tears from eyes), giddiness, hypersalivation,muscular weakness, excessive bronchialsecretion, vomiting, stomach pains, slurredspeech and muscular twitching. Lateradvanced symptoms may include diarrhoea,convulsions, coma, loss of relaxes, and loss ofsphincter control.(Note: Temephos has a very low toxicity ratingand can safely be used in drinking water tokill mosquito larvae).

CarbamatesHeadache, nausea, vomiting, bradycardia,diarrhoea, tremors, convulsive seizures ofmuscles, increased secretion of bronchial,lacrimal, salivary and sweat glands.

Pyrethroids (e.g. permethrin andS-bioallethrin)These insecticides have very low mammaliantoxicity, and it is deduced that only singledoses above 15 gm could be a serious hazardto an adult. In general, the effective dosages

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of pyrethroids for vector control are muchlower when compared with other majorgroups of synthetic insecticides. Althoughpyrethroids may be absorbed by ingestion,significant skin penetration is unlikely.Symptoms, if they, develop, reflect stimulationof the central nervous system. No cases ofaccidental poisoning from pyrethroids havebeen reported in humans. Some pyrethroids,such as deltamethrin, cypermethrin andlambdacyhalothrin, can cause eye and skinirritation if adequate precautions are nottaken.

Bacterial insecticide Bacillusthuringiensis H-14 and insect growthregulators (Methoprene)

These control agents have exceedingly lowmammalian toxicity and cause no side-effects.They can be safely used in drinking water.

4. Treatment of acuteinsecticide poisoning

l Know the symptoms of poisoning due todifferent insecticides.

l Call a physician.l Begin emergency treatment in the field.

This treatment is continued duringtransport and ends in a medical centre.

l Provide supportive treatment for thepatient. This may include:– Artificial respiration if spontaneous

respiration is inadequate.– A free airway must be maintained.

Excess vomitus and secretions shouldbe removed.

– Oxygen therapy for cyanosis (a blue orpurplish discoloration of the skin dueto insufficient oxygen).

l Decontaminate the patient as soon aspossible. This may involve:– Removal of contaminated clothing.– Thorough washing of the skin and hair

with soap and water.– Flushing contaminated eyes with water

or saline solution for 10 minutes.– Evacuation to fresh air.

l Eliminate the poison. Determine whetherthe insecticide is in water emulsion orpetroleum solution, if possible.– If the insecticide is dissolved in a water

emulsion, induce vomiting by putting afinger or spoon down the throat. If thisfails, give one tablespoon of salt in a glassof warm water until vomitus is clear.

– If the insecticide is dissolved in apetroleum product, have the doctor ornurse perform gastric lavage, suckingthe insecticide out of the stomach witha tube to prevent the possibility of thepetroleum product entering the lungsand causing pneumonia.

– Administer a laxative such as epsomsalts or milk of magnesia in water toeliminate the insecticide from thealimentary tract. Avoid oily laxatives,such as caster oil, which might increasethe absorption of insecticide.

l Administer an antidote, where possible.This involves the following steps:– The insecticide container must be

made available to the physician,wherever possible. This will help indetermining the group of insecticidesinvolved in the poisoning. The label willindicate if it is a chlorinated hydro-


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carbon, an organosphosphate, acarbamate, a pyrethroid or a bacterialinsecticide.

– If the insecticide is an organo-phosphate, either airopine sulphateor a 2-PAM chloride (Pralidoximechloride) can be used as an antidote.An injection of 2 to 4 mg atropinesulfate is given intravenously. More

atropine may be required dependingon the severity of the poisoning. Thedose of 2-PAM chloride is 1 gm for anadult and 0.25 gm for an infant.

– If the insecticide is a carbamate,atropine sulphate is used as anantidote. 2-PAM and other oximes arenot to be used.


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Annex XIIRequirements for Sustainable Community Participation

in Vector-borne Disease Control

Technologies

Proven needs(down to earth)visible

Approaches

HolisticSustainable

Inputs

HealthEducationSeed money/material

Processes

ParticipatoryHarmonious

Outputs

Address feltneeds

Inter- and intra-sectoralcooperation

Incentive/income-linkedschemes

Voluntary agenciesCommunity leaders

ResearchTrainingHealth Education

CulturalSocioeconomic

Support structuresQuality of input

Political andsocial willCommunity motivation

DiseasePrevalence

Vector control, parasite control, and improved economy and environment

Source: WHO, Geneva, Technical Report Series, 857.

Influencing factors

Supported by

Requirements

Result

Impact

Cost-effective and sustainable vector-borne disease control


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Annex XIIIFunctions of Emergency Action Committee (EAC)

and Rapid Action Team (RAT)

related to health education andcommunity participation.

(B) Rapid Action Team (RAT)

Constitution

The RAT at state/provincial levels willcomprise epidemiologists, entomologists, anda laboratory specialist at state and local levels.

Local Levels

Medical officer, public health officer, non-health staff, local government staff.

Functions

l Undertake urgent epidemiological andentomological investigations.

l Provide required emergency logisticalsupport, e.g. delivery of medical andlaboratory supplies to health facilities.

l Provide on-the-spot training in casemanagement for local health staff.

l Supervise the elimination of breedingplaces and application of vector controlmeasures.

l Carry out health education activities.l Sample the collection of serum

specimens.

(A) Emergency Action Committee(EAC)

Constitution

The EAC will comprise administrators,epidemiologists, entomologists, clinicians andlaboratory specialists, school health officers,health educators, and representatives of otherrelated sectors.

Functions

(a) To take all administrative actions and tocoordinate activities aimed at the manage-ment of serious cases in all medical carecentres and undertake emergency vectorcontrol intervention measures.

(b) To draw urgent plans of action and resourcemobilization in respect of medicines,intravenous fluids, blood products, insecti-cides, equipment and vehicles.

(c) To liaise with intersectoral committees inorder to mobilize resources from non-health sectors, namely Urban Develop-ment; Ministry of Education; Ministry ofinformation; Legal Department;WaterSupply; Waste Disposal, and Informationfor the elimination of Breeding Potential ofAedes aegypti.

(d) To interact with the news media andNGOs for dissemination of information

Source: Management of Dengue Epidemic, WHO/SEARO, May 1997

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Annex XIVCommunity Actions for Aedes Control

during Epidemics

Community activities againstlarvae and adult mosquitoescan include:l Cleaning and covering water storage

containers;l Keeping surroundings clean and

improving basic sanitation measures;l Burning mosquito coils to kill or repel

mosquitoes;l Burning coconut shells and husks to repel

mosquitoes and also eliminate thesepotential outdoor breeding sites;

l Screening houses, particularly bedrooms;l Making available hand aerosols for killing

mosquitoes;l Clearing weeds and tall grass to reduce

the available outdoor resting places foradult mosquitoes near houses, and

l Using mosquito nets to protect infants andsmall children from bites during the daytime, and also insecticide-treatedmosquito nets and curtains to killmosquitoes attempting to bite through thenets or resting on the nets or curtains.

Specific activities for controllinglarvae are:l Collection, removal, disposal, burying or

burning of all unusable tin cans, jars,bottles, tyres, coconut shells and husks,cocoa pods and other items that cancollect and hold water.

l Keeping tyres, metal boxes, discardedappliances, sinks, basins, vehicle framesand parts of other items on industrial andcommercial premises in sheltered areasprotected from rainfall.

l Arranging clean-up campaigns once ortwice a year by the local health authoritiesor community leaders in order to collectand remove all unusable containers andpotential breeding sites in and aroundhouses.

l Turning 200-litre water drums and smallearthen jars upside down once a week.This emptying and cleaning procedure iseasier when the water level is low.

l Periodically scrubbing the inside of watercontainers to destroy Aedes eggs at thetime of container cleaning.


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l Regularly emptying the water in flowervases in houses and offices at least once aweek.

l Properly covering 200-litre water drumswith burlap bags or other material whichallows rainwater, but not mosquitoes toenter .

l Covering large volume (500 litres+) waterstorage tank inlets and overflow outletswith mosquito wire mesh.

l Shredding or cutting old tyres into flatpieces and disposing of them in properlyconstructed and managed landfills awayfrom populated areas.

l Turning canoes and small fishing boatsupside down.

l Cleaning roof gutters and placing salt inant traps.

l Construction of rectangular cement watertanks with a plug at the bottom to alloweasy drainage for weekly cleaning.

l Puncturing holes in tyres used forrecreational purposes by children inschools, parks and beaches.

l Draining waterlogged tree holes.l Turning tin cups used to collect sap from

rubber trees in rubber plantations upsidedown when not in use.

l Levelling or filling-in the tops of bamboofences to prevent the accumulation ofwater and breeding sites.

l Filtering water from one container toanother through cloth in order to trap anddislodge larvae and pupae.

l Pouring boiling water into small earthen-ware jars to kill larvae when the water levelis low.

l Scrubbing down the sides of jars to killmosquito eggs.

l Removing small copepod crustaceans ofthe genus Mesocyclops from ponds orlakes and placing several of them in waterstorage containers to kill mosquito larvae.

l Removing small larvivorous fish from apond, stream or canal and placing one ortwo of them in water storage containers tokill larvae.


Dengue Regional Guidelines on Dengue DHF Prevention & Control Searo-29

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