Disease Name

Western Equine Encephalitis

Vector Information

Transmitted by Culex and Culiseta mosquitoes, western equine encephalitis virus (WEEV) is an arbovirus of the family Togaviridae. Transmission to humans occurs primarily from the bite of an infected mosquito, which most likely acquired the virus from a bird, often from an American crow or other Corvid species. Prevention techniques center on avoiding mosquito bites and include use of Environmental Protection Agency-registered insect repellents, mosquito nets, wearing long-sleeved clothing, and controlling mosquito populations around the home. 

Birds are the reservoir host of WEEV while humans and other mammals are dead end hosts incapable of directly transmitting the disease since human blood virus levels are not high enough to directly infect a mosquito. Most infected individuals are asymptomatic, however symptoms including fever and headache can develop seven to 21 days post infection.Severe disease can develop in a small subset of people, primarily in the very old and young, and is demonstrated as encephalitis, delirium, disorientation, coma, paralysis, and death. Irreversible neurological damage can occur in infants and young children. The case fatality rate for WEEV infection overall is approximately four percent and between five and 15 percent for severe cases. Around half of infants with severe WEEV infection will experience irreversible brain damage. No vaccines for WEEV exist and treatment is symptomatic.