Dengue: An emerging arboviral disease

Dengue:An emerging arboviral disease

Gary G. Clark, Ph.D.Mosquito and Fly Research Unit

CMAVE, ARS, USDAGainesville, Florida

First interaction with a Navy physician

My “emergence” at Balboa Naval Hospital

San Diego, California

Discussion topics

Epidemiology of dengue and DHF Emergence of dengue in the

Americas Aedes aegypti and its development Adult control methods for Ae.

aegypti Evaluation of emergency control

studies (CDC and the military) Dengue and the US military

Dengue virus

An arbovirus; transmitted by mosquitoes Four virus serotypes (DEN-1, 2, 3, 4);

single-stranded RNA Family Flaviviridae (WNV, SLE, YF, JE) Causes dengue (headache, fever,

joint/retrorbital pain, rash, bleeding) and dengue hemorrhagic fever (DHF)

Dengue viruses Each serotype provides specific lifetime

immunity and short-term cross-immunity All serotypes can cause severe and fatal

disease Genetic variation within serotypes; some

appear to be more virulent or have greater epidemic potential

Can produce outbreaks/epidemics

in urban areas

Transmission of dengue virusby Aedes aegypti

Viremia Viremia

Extrinsic incubation

period

Days

0 5 8 12 16 20 24 28

Human #1 Human #2Illness

Mosquito feeds /acquires virus

Mosquito refeeds /transmits virus

Intrinsicincubation

period

Illness

Dengue: A global perspective*

Most important arboviral disease of humans; 2.5- 3 billion people (40% of the world) at risk of infection

10’s of millions of cases of dengue and 100’s of thousands of DHF cases annually

A leading cause of hospitalization and death among children in Asia

DHF mortality rate averages about 5%

* Source: WHO, 1996

World distribution of dengue 2006

Areas infested with Aedes aegypti

Areas with Ae. aegypti and recent dengue epidemics

Dengue/DHF cases reported to the World Health Organization

1955-2005*

0

200000

400000

600000

800000

1000000

1955-1959

1960-1969

1970-1979

1980-1989

1990-1999

2000-2005

* Source: WHO, Sep. 2006

Ave.annual

no. cases

Dengue in the Americas1980 – 2006*

0

200,000

400,000

600,000

800,000

1,000,000

1980 1985 1990 1995 2000 2005

Cases

* Source: PAHO (Jan. 19, 2007)

Year

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

1980 1985 1990 1995 2000 2005

* Source: PAHO (Jan. 19, 2007)

Dengue hemorrhagic feverin the Americas

1980 – 2006*

Year

Cases

*

Presence of competent mosquito Presence of competent mosquito vectorvector

Large, susceptible human populationLarge, susceptible human population Conditions supporting abundant Conditions supporting abundant

mosquito populationmosquito population Frequent introduction of dengue Frequent introduction of dengue

virusesviruses Ineffective vector control programsIneffective vector control programs

Why has dengue emergedin the Americas?

Population increase

Emergence of dengue Socio-economic factors

1830 1930 2000

Billion

6

5

4

3

2

1

Unprecedented population increase

Uncontrolled and unplanned urbanization

Inadequate environmental conditions

Reinfestation of the Americas by Aedes aegypti* 1930s1930s 1970 1970 2006 2006

* Source: CDC/PAHO

Emergence of dengueUncontrolled urbanization*

In 1954, 42% of the population of Latin America lived in urban areas, increasing to 75% in 1999.

“Informal” communities proliferated as a result of poverty.

Scarcity of basic services: running water, sewage and collection of garbage.

* High population density

Sources: Gubler, 1998. PAHO, 1997.

Urban and rural populations in Latin America

Emergence of dengue Inadequate environmental conditions*

Insufficient collection of disposable containers

Non-biodegradable containers

Discarded tires

Insufficient and inadequate water service

Increased number of “pilas” and water storage containers

Inadequate water and sewer conditions

* Increase in production sites

Buckets and pails

Production sites for Aedes aegypti

Water storage tanksWater storage tanks

Production sites for Aedes aegypti

Production sites for Aedes aegypti

Discarded tires

Emergence of dengue Population movement*

Migrations

International Tourism

More than 750 millon people cross frontiers annually

Increase of migration from rural areas to cities

1.4 billion international passengers in 1999

697 million international tourist arrivals in 2000.

715 million in 2002, an increase of 3.1%

Source: WTO

* Traffic of microorganisms

Rural and urban populations in Latin America

Years

Pe

rce

nt

Why has dengue emergedin Latin America?

Reinfestation by Aedes aegypti Ineffective mosquito control programs Deteriorated public health infrastructure Uncontrolled population growth and

unplanned urbanization Increased air travel by humans

Aedes aegypti

Aedes aegypti

Lives in and around human habitations in urban areas

Lays eggs and produces larvae preferentially in artificial containers

Strong preference for human blood; primarily a daytime feeder and bites several times in her life

Most important vector of dengue viruses in the world

Life cycle of Aedes aegypti

1. Eggs

2. Larvae

3. Pupae

4. Adult

Personal protection against mosquitoes

Apply repellent (20-30% DEET) to exposed skin- avoid eyes, mouth, and children’s hands

Spray clothing with repellents with DEET or permethrin

Use treated mosquito netting over bed Spray insecticide in room before going to bed,

follow label instructions Wear long-sleeved shirts and long pants

Dengue vaccine?

No licensed vaccine at present Effective vaccine must be tetravalent Field testing of an attenuated tetravalent

vaccine currently underway Effective, safe and affordable vaccine will

not be available in the immediate future

Vector control continues to be key to dengue prevention

Vector control methods:Biological and environmental control

Biological control• Largely experimental

• Option: place fish in containers to eat larvae

Environmental control• Elimination of larval habitats

• Method most likely to be effective in the long term

Thermal fog Aerosols – Cold fog and ultra low

volume (ULV) • Inside of residences with portable

equipment• From the ground with vehicle-

mounted equipment • Aerial application

Spraying to control adult Aedes aegypti

CDC evaluations: Emergency control in Puerto Rico* Ground ULV applications versus Aedes

aegypti C-130 (Hercules transporter) with USAF

Reserve Unit from Columbus, OH US Navy (DVECC) with PAU-9 from JAX Mosquitoes susceptible to naled

(Dibrom 14) and insecticide reached the ground but did not penetrate houses

Limited, transitory impact on wild population

* Other projects with US Army in Honduras and the Dominican Republic

Ground ULV application

Ground ULV application

Aerial application in San Juan with C-130

Aerial application in San Juan with PAU-9

US Navy’s PAU-9 unit

Indoor application with thermal fog unit

Indoor application with portable ULV unit

Operation Restore Hope Somalia- 1992-1993

30,000 troops deployed; 530 were studied

- 289 hospitalized with fever- 129 with “unspecified illness”- 41 with DEN virus and 18 with anti-dengue ABs= 59/129 (46%) with DEN infections.

Study of unit in Baardera: 9% (44) of 494 with dengue infections

70% used DEET < 1 time/day, 22% never treated uniforms, 61% did not use bed nets and only 25% kept sleeves rolled down at all times

Poor compliance with PPMs vs. insects

Operation Uphold DemocracyHaiti- 1995

249 with fever- 79 (32%) with DEN infection- 44/79 participated in survey- 73% with mosquito bites daily- 50% used repellents < 1/week or never- 48% did not use a bed net

10/14 (71%) of Army units did not have deployed, functional field sanitation teams

31% of soldiers indicated PPMs emphasized “some but not enough or not at all”

Low unit readiness to perform VC activities Command enforcement of PM doctrine is

essential for dengue prevention

DHF in Venezuela 1989-1990 PAHO-Venezuela requested that CDC-San Juan

test specimens from suspected fatal case (12 year-old girl) of DHF from Venezuela

Dengue etiology was confirmed; epidemic was spreading from Maracay to Caracas

Minister of Health sought epidemic response recommendation. Discussed results of USAF and Navy trials. “Aerial control… limited impact, dangerous, could not recommend aerial control as the solution.”

Minister “… must take action and intended to spray using helicopters with booms attached”

With Minister’s decision, I changed hats and recommended that he seek “professional assistance such as from the US Navy” No aerial spray experience in Venezuela.

Venezuelan Air Force transported DVECC personnel and equipment to Venezuela.

LCDR Mark T. Wooster, MSC, USNNavy Medicine (Mar-Apr 1991)

Preparing to spray with Venezuelan helicopter

MMART* Preventive MedicineAssists Venezuela

* Mobile Medical Augmentation Readiness Team

DHF in Venezuela 1989-1990 DVECC’s “equipo de expertos rociadores

aereos”• LCDR Mark Wooster• LT Joseph Conlon• LT Stanton Cope• LT David Claborn• LT Rafael del Vecchio

U.S. Navy personnel performed 60 aerial spray missions (malathion @ 3 oz/acre) during 135 flight hours over Maracay and Caracas.

Aterriza de emergencia helicópterode fumigación (Newspaper report)

MARACAY (Especial) – Uno de los helicópteros

de la Fuerza Aérea, que participa en las operaciones de fumigación contra el dengue, aterrizó de emergencia

en el estacionamiento del centro comercial “El Castaño”, de esta ciudad, resultando gravemente herido el piloto de

la unidad, que no fue identificado por las autoridades.

En la aeronave viajaban dos oficiales [LT Joseph Conlon and LT Stanton Cope] de la Marina de los

Estados Unidos, quienes habrian sufrido lesiones. Tambien

ibandos oficiales de la Fuerza Aérea Venezolana, y tres guardias nacionales.

La aeronave arrancó una linea de alta tensión y dejo al sector “El Castaño” sin electricidad.

Venezuelan helicopter

After mission!

Fortunately, the injuries to the crew and US Navy personnel were minor.

And, some of our “expertos” developed a new feeling for helicopters on the ground.

“Private parking space” for AFPMB RLOSilver Spring, Maryland

“I love my choppers!”

CAPT Stanton E. Cope- “Dengue fighter”

uubbss

Take home messages Importance of command emphasis for

personal protection measures Critical that you lead by example and use

repellents Be prepared to respond to requests for help in

dealing with dengue and other VBD in support of US military or in humanitarian missions

There is no “magic bullet” to solve the emerging problem of dengue/DHF

You are part of unique national/international vector control resources; challenges and danger may accompany your work

USDA is anxious to support US military in protecting deployed personnel and in responding to humanitarian missions

My last interaction with an Army physician

Walter Reed Army Medical Center

Washington, D.C.

PSA