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11 Cards in this Set

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West Nile Virus: Etiology
1) enveloped, + strand RNA
2) flaviviridae, genus flavivirus
3) highly pathogenic for horses and birds
WNV: Transmission
1) mosquitoes to spread it among birds
2) Different mosquitoes to spread virus from birds to mammals
WNV: Susceptible species
1) mosquitoes: replicates in intestine and salivary glands; small percentage of mosquitoes in an anedmic area actually carry the virus
2) Birds: fatal in crows, blue jays, ravens; high level of viremia for 1-4 days
3) Horses
4) Humans: <1% get severe clinical signs; if severe clinical signs develop after an incubation period of 3-15 days, fatality rate is 3-15%
5) recentaly, dogs and squirrels
6) Serological evidence of infection in other species
WNV 2007
MT and CA had highest number of equine WNV
Clinical signs
1) Birds: corvids most susceptile, acute clinical signs, birds usually found dead and submitted for testing
2) Horses: mostly seen in older horses, acute onset ataxia, weakness, paresis of hind legs, paraparesis, progressing to tetraplegia and recumbency, low-grade fever or no fever, marked hypmetria, muscle fasiculations (common in horses). Less common signs: anisiocoria, slow PLR, seizure, head tremors, lip twitching, tongue paralysis, hypersensitivity to ligh/sound, somnolence, falling to knees
3) Humans: subclinical, fever, meningoencephalitis
Lesions
1) Birds: heart muscle, kidney, brain
2) Horses: Brian-- nonsuppurative encephalomyelitis, perivascular cuffs, glial nodules and focal gliosis in the grey matter; Spinal cord-- non-suppurative inflam, possible neuronal degeneration, neuronophagia, gliosis
Diagnosis
1) clinical signs
2) gross and histo lesions
3) virus isolation-- need BSL-3 lab
4) IHC-- don't use in horses
5) IgM capture ELISA
6) RT-PCR-- fresh (BSL-3) or formalin fixed tissue (not as good)
7) IgG ELISA (not used much)
8) Plaque reduction neutralization test (not used)
WNV diagnosis in dead horses
1) submission of heads or whole bodies to DCPAH for necropsy
2) MDA will arrange for transportation if necessary
Other testing of live equine suspects
1) IgG ELISA: screening test for previous exposure (vacc or natural)--NOT USED
2) VN: determines Ab titer. Most common for horses
Control
1) mosquito control (reduce breeding sites)
2) limit exposure ot mosquitoes
3) supportive therapy
4) prevention of self-inflicted injuries in horses
Prevention
1) inactivated vaccine for horses: Primary series-- two doses IM, 3-6 wks apart; yearly booster
2) vector vaccine by Merial. canarypox vector
3)intervet-- vector vacc w/ flavi vector (1 yr immunity w/ 1 dose)