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

I. Virus 2

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

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

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

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

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

II. Vector

Aedes aegypti Mosquito 8

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

Aedes aegypti Breeding Sites

III. Epidemiology

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

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

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

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

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

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

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

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