West Nile Virus (WNV) is a viral and vector borne disease. Birds are the virus reservoirs from which mosquitos feed and transmit the virus to the horse.

Incubation: The incubation period is the time from exposure to the virus to when a horse shows clinical signs of infection. The incubation period for WNV is seven to ten days.

Transmission: WNV is transmitted by infected mosquitoes that bite horses.

Clinical Signs: Signs include depression, fever, lack of appetite, lethargy, neurologic signs (such as muscle fasciculations or twitches in the shoulder area), and ataxia.

Diagnostic Testing: Serum ELISA tests can be used to diagnose WNV infection.

Treatment: There is no treatment for WNV. Supportive care can be provided for horses who show clinical signs.

Prevention: Keeping horses vaccinated is the primary prevention method for WNV. Boosters and revaccinations should occur following AAEP’s guidelines. Vector management can also prevent WNV. Use insect repellants on horses, fans in barns, and eliminate standing water.

Prognosis: The prognosis is good for vaccinated horses, but unvaccinated horses have a higher case fatality rate. Horses who survive infection tend to make a full recovery.