west nile virus
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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. - 2002WNV Activity in the U.S. - 2002
Western Hemisphere
North America currently only has experience with related SLE-a sporadic illness hereCentral 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 SpeciesSusceptible Corvid Species
Blue jay
American crow
Common raven
WNV Activity in Birds - 2001WNV Activity in Birds - 2001
WNV activity in Michigan - 2001WNV activity in Michigan - 2001
585 birds submitted
244 birds tested
38 counties
participated
65 positive birds,
in 10 counties
WNV Positive Birds 2002
WNV Activity in Michigan - 2002WNV Activity in Michigan - 2002Bird SurveillanceBird 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 2002Fatality rate 30%Dead-end host-viremia low and briefCS: weakness, ataxia, muscle twitchingDX: tissues-VI, PCR
serum-IgM ELISA, PRNTVaccine: Fully licensed
Interferes with PRNT Pregnant mare?
329 Equine Cases
Positive Equine WNV Counties 2002