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Dengue. Virus, Vector and Epidemiology. I. Virus. 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). Dengue Viruses.

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Dengue l.jpg

Dengue

Virus, Vector and Epidemiology


I virus l.jpg

I. Virus


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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)


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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


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Extrinsic

incubation

period

Illness

Illness

Transmission of Dengue Virusby Aedes aegypti

Mosquito refeeds /

Mosquito feeds /

transmits virus

acquires virus

Intrinsic

incubation

period

Viremia

Viremia

0

5

8

12

16

20

24

28

Days

Human #1

Human #2


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1

2

4

3

Replication and Transmissionof Dengue Virus (Part 1)

1. Virus transmitted

to human in mosquito

saliva

2. Virus replicates

in target organs

3. Virus infects white

blood cells and

lymphatic tissues

4. Virus released and

circulates in blood


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6

7

5

Replication and Transmissionof Dengue Virus (Part 2)

5. Second mosquito

ingests virus with blood

6. Virus replicates

in mosquito midgut

and other organs,

infects salivary

glands

7. Virus replicates

in salivary glands


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II. Vector


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Aedes aegypti Mosquito


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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


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Aedes aegypti Breeding Sites


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III. Epidemiology


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Areas infested with Aedes aegypti

Areas with Aedes aegypti and recent epidemic dengue

World Distribution of Dengue1999


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Reported Cases of Denguein the Americas, 1980 - 1998

*Provisional data for 1998


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Mean Annual Number of DHF CasesThailand, Indonesia and Vietnam, by Decade

* Provisional data through 1998


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Reported Cases of DHF inthe Americas, 1970 - 1998

* Provisional data through 1998


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Distribution of DEN-3in the Americas, 1998

1994

1995

1997

1998

Pan American Health Organization, 1999


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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


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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


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Challenges for the Future

  • 2.5 billion people at risk world-wide

  • In the Americas, 50-fold increase in reported cases of DHF (1989-1993 compared to 1984-1988)*

  • Widespread abundance of Aedes aegypti in at-risk areas

* Organization of American States,

Human Health in the Americas, 1996


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