Recent Equine Deaths from West Nile Virus in Upstate NY
Horse have recently died from West Nile Virus (WNV) in upstate NY counties, with cases diagnosed in Orleans, Tompkins, Livingston, Erie, Genesee, St. Lawrance and Clinton Counties. WNV has been found in Yates County in past years, making the horses within our practice area at risk for contracting WNV. This disease causes encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord) in humans and horses. The mortality rate of horses infected with WNV is high, and most horses are euthanized for humane reasons or die spontaneously. Due to the mosquito vector, WNV cases are seen during the summer and fall months, with September and October being times of peak incidence of this disease.
Because there is no specific treatment for WNV, annual vaccination is highly recommended.
WNV is transmitted to horses via the bite of a mosquito. Mosquitoes may pick up the virus when they take a blood meal from wild birds (e.g. crows) that are infected. Those mosquitoes may then transmit the virus to people and other animals when taking a subsequent blood meal. Once infected, the virus travels to the central nervous system. Horses infected with WNV may initially present with the nonspecific clinical signs of fever, lethargy and decreased appetite. The onset of neurologic symptoms is sudden and progressive, and might include a change in personality (hyperexcitability or aggression), development of muscle fasciculations (tremors), abnormal gait, incoordination of movements (ataxia) and cranial nerve abnormalities (head tilt, facial nerve paralysis, inability to swallow). Neurologic deficits may progress to the horse becoming unable to stand.
A definitive diagnosis of WNV can be made using a blood test or through analysis of cerebral spinal fluid or brain tissue (after death). With aggressive medical management and supportive care, some horses will begin to show improvement several days after the onset of clinical signs. Over several months a full recovery can sometimes be achieved in these horses.