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

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

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

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

WNV Surveillance

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

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

WNV Activity in the U.S

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

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

Susceptible Corvid Species Blue jay American crow Common raven

WNV Activity in Birds

WNV activity in Michigan birds submitted 244 birds tested 38 counties participated 65 positive birds, in 10 counties

WNV Positive Birds 2002

WNV Activity in Michigan Bird Surveillance 766 birds submitted 588 birds tested 80 counties participated 73 of 83 counties with positive birds

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

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

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)

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

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?

329 Equine Cases Positive Equine WNV Counties 2002