Western equine encephalitis virus (WEEV) is a mosquito-borne virus that primarily affects horses and humans. It is part of the Togaviridae family and is transmitted through the bite of infected mosquitoes, particularly Culex species. Symptoms in humans can include fever, headache, and in severe cases, neurological complications. WEEV is most commonly found in the western United States and Canada, especially during the summer months when mosquito populations are high. While the virus can lead to serious illness, most infections are mild or asymptomatic. Vaccines are available for horses to help prevent the disease.