West Nile Virus

1. West Nile Virus Kimberly Signs, DVM Michigan Department of Community Health

2. West Nile Virus • Found in Africa, West Asia, Eastern Europe, and the Middle East • Emerging Infectious Disease • Flavivirus Family • Japanese Encephalitis Group • Closely related to St. Louis Encephalitis virus

4. Electron micrograph of West Nile virus isolated from the brain of a crow in New York

5. Pathogenicity of Virus • Previous outbreaks in Africa not associated with significant bird or human morbidity or mortality • NYS 1999 strain essentially the same as that associated with stork and goose mortality in Israel • Different lineages of WNV

7. WNV Surveillance

8. Types of Surveillance Activity Used by Public Health: • Passive -rely on receipt of reports • Active -efforts made to receive reports or perform testing • Sentinel –groups of susceptible animals placed and sampled to provide early warning of disease • Special –focused studies

9. Surveillance for WNV • Crows/Corvids • Veterinary (Horses) • Mosquitoes • Humans All types employ both active and passive surveillance activities to some degree.

12. WNV Activity in the U.S. - 2002

13. Western Hemisphere • North America currently only has experience with related SLE-a sporadic illness here • Central and South America-other flaviviruses more prevalent-Dengue, Yellow Fever (vaccine) • Southern spread may be hindered by immunity to these other flaviviruses

14. WNV Infection in Birds • most birds are simply found dead • clinical signs may include incoordination, weakness, tremors, abnormal head posture • some are asymptomatic

15. Susceptible Corvid Species Common raven Blue jay American crow

16. WNV Activity in Birds - 2001

17. WNV activity in Michigan - 2001 • 585 birds submitted • 244 birds tested • 38 counties participated • 65 positive birds, in 10 counties

18. WNV Positive Birds 2002

19. WNV Activity in Michigan - 2002Bird Surveillance • 766 birds submitted • 588 birds tested • 80 counties participated • 73 of 83 counties with positive birds

20. Bird Ecology • Competence: Passerine birds • WNV found in 162 species of birds to date • Reservoirs need to be abundant and exposed to the infection • Sero-prevalence: 30% in epizootic areas

21. Transmission in Birds • Mosquitoes: (ticks? biting flies?) • Contact:Experimental w/ crows Virus high-oral and cloacal • Oral:Experimental w/ infected bird and mammal carcasses-birds can have high levels of virus in tissues up to 14 days after viremia is cleared

22. Vector Ecology • Primarily Culex species involved (bird biters), container breeders • Bridge vectors (bite birds and mammals) • Over-wintering in adults (sewer systems) • Vertical Transmission in some species (+ male mosquitoes)

23. Environmental Determinants • Competent vector and host must occur together with virus • Temperature conditions affect transmission • Appropriate mosquito habitat

24. Equine Surveillance • ~15,000 cases in 2002 • Fatality rate 30% • Dead-end host-viremia low and brief • CS: weakness, ataxia, muscle twitching • DX: tissues-VI, PCR serum-IgM ELISA, PRNT • Vaccine: Fully licensed Interferes with PRNT Pregnant mare?

25. Positive Equine WNV Counties 2002 329 Equine Cases