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West Nile Virus

West Nile Virus. Epidemiology of the North American outbreak. Mira J. Leslie State Public Health Veterinarian Washington State Department of Health. Learning Objective.

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West Nile Virus

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  1. West Nile Virus Epidemiology of the North American outbreak Mira J. Leslie State Public Health Veterinarian Washington State Department of Health

  2. Learning Objective • West Nile virus is established in North America. The magnitude of the ongoing WNV outbreak is extraordinary and our knowledge is incomplete. • Definitions: • Arbovirus = arthropod-borne virus Epizootic = epidemic in animals

  3. Do you remember when?Encephalitis- NYC 1999 • SLE cases reported in Queens • Active ph surveillance identified additional cases of encephalitis • Causative agent unknown in many cases

  4. Bronx Zoo • Zoo collection birds and birds in community (crows) dying. • Veterinary pathologist pursued testing. • West Nile virus isolated for the first time in Western Hemisphere.

  5. Initial outbreak

  6. West Nile virus: history • June 10, 323BC: Alexander the Great died in Babylon. (www.cdc.gov/ncidod/EID/vol9no12/03-0288.htm) • 1937:First identified (human illness) West Nile district of Uganda. • 1937- 1990’s: Mild disease/ meningoencephalitis Middle East and Africa • 1996 – 1999: Severe neurologic disease in Romania, Israel, Russia

  7. West Nile Virus- the organism 2000-2004 Davis CT, Beasley DWC, Guzman H, Raj P, D’Anton M, Novak RJ, et al. Genetic variation among temporally and geographically distinct West Nile virus isolates, United States, 2001, 2002. Emerg Infect Dis 2003 Nov

  8. History of Arbovirus Outbreaks in North America CDC data

  9. Distribution of WNV activity, 1999-2003 1999 2002 2000 2003 2001

  10. West Nile Virus, Human Cases 2002 epicenter 2003 epicenter

  11. West Nile Virus in the US How did it get here?Possible Pathways of Introduction • Infected human host • Human-transported vertebrate host • Legal • Illegal • Human-transported vector(s) • Storm-transported vertebrate host (bird) • Intentional introduction (terrorist event)-not

  12. West Nile virus – transmission cycle Vector mosquito Incidental hosts Reservoir host -birds

  13. Mosquitoes: WNV vectors • 37 species of native mosquitoes have tested positive in the U.S. 1999-2003. • Some mosquitoes are more competent vectors than others. Environmental factors including climate play a role. • Culex species including Culex tarsalis in the west are principal arbovirus vectors.

  14. Birds: WNV reservoir hosts • More than 225 species have been reported to be infected with WNV. • Crows and jays predominate with a high fatality rate. • Variable experiences: Chicago vs. Connecticut.

  15. Learning about avian reservoirs of WNV Most competent reservoirs: Blue jay, Common grackle, House finch, American crow, House sparrow Transmission routes: mosquitoes, ingestion, and bird-bird contact. Some birds have persistent infection in many organs including skin. Komar et al. Experimental Infection of North American birds with the New York 99 strain of West Nile Virus, Emerg Infect Dis, Vol 9, No. 3, March 2003

  16. Dead birds as early indicators of WNV activity

  17. Horses • In 2002, an intense epizootic of equine WNV infection occurred (> 14,500 reported cases). • Two new vaccines are licensed for use in horses. • Horses do not develop sufficient viremia to amplify the virus.

  18. Bats Squirrels, Chipmunk Skunk; Rabbit Goat, sheep, llama, deer… Zoo animals Harbor seal (Non-human) Primates Farmed Alligators…. In addition to humans,bugs, birds, and horses

  19. West Nile infection, U.S., 2003 • Human illness: 9862Fatality: 264 • Corvid (crow, jay): 10,200 Other bird: 1866 • Mosquito pools: 8384 • Equine: 5145 • Sentinel flocks: 1956 • “Other” animals: 48 • Canine: 37 Squirrel: 20 Feline: 1

  20. West Nile virus WNV activity, U.S. Jan 1- June 1, 2004:

  21. WNV Seasonality

  22. West Nile virus Surveillance/Response: Partnerships • Public Health agencies • Health care providers, laboratories • Blood banks • Wildlife agencies and orgs • Zoos • Entomologists, ecologists, cartographers • Veterinarians, veterinary laboratories • Universities The public, the media, and others ……….

  23. Arbonet, CDC Human cases, 2004 • “Tracking the virus in real-time” Secure web-based reporting • Compiles data on humans, birds, mammals, sentinel flocks, mosquitoes, etc. • Humans recorded by syndrome and status • Real-time mapping-USGS

  24. Take home messages West Nile virus: • Established ecological niche in North America • WNV outbreaks are unpredictable and our understanding is rudimentary. • Management: flexibility, coordination, partnerships • Plan surge capacity.

  25. Who is this “human”? QUESTIONS?

  26. West Nile virus-important issues • Laboratory testing • Public health labs,commercial labs • Veterinary labs • Test development • Communications • Health Alert messaging • Prevention messaging • Strategies and target audiences

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