1. Virus, Vector and Epidemiology
Dengue
Virus, Vector and Epidemiology 1

2. I. Virus 2

3. Dengue Virus Causes dengue and dengue hemorrhagic fever
Is an arbovirus
Transmitted by mosquitoes
Composed of single-stranded RNA
Has 4 serotypes (DEN-1, 2, 3, 4) 3

4. 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 genetic variants within each serotype appear to be more virulent or have greater epidemic potential 4

5. 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
Days
Illness
Illness
Human #1
Human #2 5

6. Replication and Transmission of Dengue Virus (Part 1)
1. Virus transmitted
to human in mosquito
saliva 2
2. Virus replicates
in target organs 4 3
3. Virus infects white
blood cells and
lymphatic tissues
4. Virus released and
circulates in blood 6

7. Replication and Transmission of Dengue Virus (Part 2)6
5. Second mosquito
ingests virus with blood
6. Virus replicates
in mosquito midgut
and other organs,
infects salivary
glands 7 5
7. Virus replicates
in salivary glands 7

8. II. Vector

9. Aedes aegypti Mosquito8

10. Aedes aegypti Dengue transmitted by infected female mosquito
Primarily a daytime feeder
Lives in and around human habitation
Lays eggs and produces larvae preferentially in artificial containers 9

11. Aedes aegypti Breeding Sites

12. III. Epidemiology

13. World Distribution of Dengue 1999
Areas infested with Aedes aegypti
Areas with Aedes aegypti and recent epidemic dengue

14. Reported Cases of Dengue in the Americas, 1980 - 1998
*Provisional data for 1998

15. Mean Annual Number of DHF Cases Thailand, Indonesia and Vietnam, by Decade
* Provisional data through 1998

16. Reported Cases of DHF in the Americas, 1970 - 1998
* Provisional data through 1998

17. Distribution of DEN-3 in the Americas, 1998
1994
1995
1997
1998
Pan American Health Organization, 1999

18. Recent Dengue in the U.S.A. (Texas)
Dengue epidemics occurred in the USA in the 1800s and the first half of the 1900s
Recent indigenous transmission:
1980: first locally acquired cases since 1945
1986: 9 cases
1995: 7 cases
1997: 3 cases
Lack of recent epidemic transmission likely due to changes in life style

19. Reasons for Dengue Expansion in the Americas
Extensive vector infestation, with declining vector control
Unreliable water supply systems
Increasing non-biodegradable containers and poor solid waste disposal
Increased air travel
Increasing human population density in urban areas

20. Challenges for the Future
2.5 billion people at risk world-wide
In the Americas, 50-fold increase in reported cases of DHF ( compared to )*
Widespread abundance of Aedes aegypti in at-risk areas
* Organization of American States,
Human Health in the Americas, 1996