1. Dengue: An emerging arboviral disease
Gary G. Clark, Ph.D.
Mosquito and Fly Research Unit
CMAVE, ARS, USDA
Gainesville, Florida 1

2. My “emergence” at Balboa Naval Hospital
San Diego, California
First interaction with a Navy physician

3. 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

4. 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) 3

5. 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 4

6. Transmission of dengue virus by Aedes aegypti
Mosquito feeds /
Mosquito refeeds /
acquires virus
transmits virus
Extrinsic
incubation
period
Intrinsic
incubation
period
Viremia
Viremia 5 8 12 16 20 24 28
Illness
Illness
Days
Human #1
Human #2 5

7. Dengue: A global perspective*
Most important arboviral disease of humans; 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

8. World distribution of dengue 2006
Areas infested with Aedes aegypti
Areas with Ae. aegypti and recent dengue epidemics

9. Dengue/DHF cases reported to the World Health Organization 1955-2005*
Ave.
annual
no. cases
* Source: WHO, Sep. 2006

10. Dengue in the Americas 1980 – 2006*
Year
* Source: PAHO (Jan. 19, 2007)

11. Dengue hemorrhagic fever
in the Americas 1980 – 2006*
Cases *
Year
* Source: PAHO (Jan. 19, 2007)

12. Why has dengue emerged in the Americas?
Presence of competent mosquito vector
Large, susceptible human population
Conditions supporting abundant mosquito population
Frequent introduction of dengue viruses
Ineffective vector control programs

13. Emergence of dengue Socio-economic factors
Population increase
Billion
1830
1930
2000
Unprecedented population increase
Uncontrolled and unplanned urbanization
Inadequate environmental conditions 6 5 4 3 2
Entre 1950 y 1960 ocurrió el mayor crecimiento de la población de la tierra, la pob se duplico en 15 anos
El tercer mundo duplica su población cada 43 anos. 1

14. Reinfestation of the Americas by Aedes aegypti*
* Source: CDC/PAHO

15. Emergence of dengue Uncontrolled 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, PAHO, 1997.

17. 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

18. Production sites for Aedes aegypti
Buckets and pails

19. Production sites for Aedes aegypti
Water storage tanks

20. Production sites for Aedes aegypti
Discarded tires

21. 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%
* Traffic of microorganisms
Source: WTO

23. Why has dengue emerged in 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

24. Aedes aegypti 8

25. 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 9

26. Life cycle of Aedes aegypti
4. Adult
3. Pupae
1. Eggs
2. Larvae

27. 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

28. 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

29. 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

30. Spraying to control adult Aedes aegypti
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

31. 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

32. Ground ULV application

33. Ground ULV application

34. Aerial application in San Juan with C-130

35. Aerial application in San Juan with PAU-9

36. US Navy’s PAU-9 unit

37. Indoor application with thermal fog unit

38. Indoor application with portable ULV unit

39. Operation Restore Hope Somalia- 1992-1993
30,000 troops deployed; 530 were studied
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

40. Operation Uphold Democracy Haiti- 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

41. DHF in Venezuela
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.

42. MMART* Preventive Medicine Assists Venezuela
Preparing to spray with Venezuelan helicopter
MMART* Preventive Medicine
Assists Venezuela
LCDR Mark T. Wooster, MSC, USN
Navy Medicine (Mar-Apr 1991)
* Mobile Medical Augmentation Readiness Team

43. DHF in Venezuela
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 3 oz/acre) during 135 flight hours over Maracay and Caracas.

44. Aterriza de emergencia helicóptero de 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 iban
dos 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.

45. Venezuelan helicopter
After mission!
Venezuelan helicopter

46. 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.

47. “Private parking space” for AFPMB RLO Silver Spring, Maryland
“I love my choppers!”
“Private parking space” for AFPMB RLO
Silver Spring, Maryland

48. CAPT Stanton E. Cope- “Dengue fighter”b s
CAPT Stanton E. Cope- “Dengue fighter”

49. 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

50. Walter Reed Army Medical Center
PSA
Washington, D.C.
My last interaction with an Army physician