West Nile Virus (WNV)
West Nile Virus (WNV) is a viral infection that causes encephalitis in equines, birds, humans and some other exotic species.
WNV is a flavivirus , from the family Arbovirus .
In North America, are thought to be the virus reservoir, while humans and equines are considered dead-end hosts. The transmission from bird to human or horse occurs through biting insects, especially the mosquito. Once the virus is introduced into the blood it travels to the circulation of the CNS where the virus attacks the blood vessels in the space and the meninges causing inflammation and blood clotting (DIC). Ischemic necrosis of the CNS tissue may occur as a result of the occlusion of blood vessels by increased intracranial pressure and blood clots. Animals that are kept at pasture during peak mosquito season and feeding times are at an elevated risk of contracting WNV. Those who are younger and unvaccinated are also at higher risk. The clinical presentation includes fever, depression, lethargy, anorexia, colic, lameness (slow short stilted gait), asymmetric ataxia, muscular weakness & atrophy, muscle fasciculations, tremors, loss of fine motor control, head pressing, wandering, dementia, hyperesthesia, aggression, paresis, CN impairments, narcoleptic like episodes, recumbency, seizure, coma and death.
Diagnosis can be made through clinical signs and symptoms, blood serology and analysis of CSF.
Treatment is largely supportive care including IV fluids, NSAID’s, DMSO, antiviral medications, catheters, feeding tubes, and slings. Euthanasia is recommended for recumbent individuals who cannot rise unassisted. Prognosis for WNV is guarded to poor, and those individuals who recover do so very slowly and or with residual ataxia & weakness. Mortality rate is 35-45%. WNV can be prevented through annual vaccination. It is recommended that vaccination be done at least three weeks before mosquito season. Some individuals experience an inflammatory reaction at the vaccination site, which can be quite painful and temporarily debilitating. It is recommended that vaccination for WNV be done separately from other annual vaccinations, or at a different site on the body than other vaccinations to lessen the incidents of adverse reaction to the vaccination.
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