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