Horses encephalitis viruses

Walton TE. Virulence properties of Venezuelan equine encephalitis virus serotypes in horses. In Venezuelan Encephalitis Proceedings of the Workshop-Symposium on Venezuelan Encephalitis Virus 14-17 September 1971. Washington, DC Pan American Health Organization 1972 134. PAHO Scientific Publication 243. 

Venezuelan equine encephalitis (VEE) is a virus that is naturally transmitted from horse to horse by mosquitoes. Humans can also get the virus from the infected mosquito. Each year, thousands of persons acquire the disease naturally from mosquito bites. Human outbreaks usually follow an epidemic among the horse population. Humans infected can infect mosquitoes for up to 72 hours. Once a mosquito becomes infected, it remains so for life. 

The initial isolation in 1930 of WEE virus from the brain tissues of a horse with encephalitis was made in the midst of a large and apparently unprecedented epizootic in California, which involved at least 6,000 horses and with approximate mortality of 50%. Cases of human encephalitis in California were not linked to WEE until 1938, when the virus was isolated from the brain of a child. During the 1930s and 1940s, several other very extensive epizootics occurred in western and north-central states, as well as Saskatchewan and Manitoba, Canada, which affected large numbers of equines and humans. For example, it has been estimated... 

Venezuelan equine encephalitis (VEE) is caused by an alphavirus that is endemic to northern South America, Central America, Mexico, and Florida. The virus causes disease in horses, mules, burros, and donkeys (Equidae), and the disease is transmitted to humans by the bite of infected mosquitoes that have previously bitten an infected animal. Many kinds of mosquitoes can transmit the virus. In natural VEE epidemics, human disease is always preceded by disease in the equine population. The disease is deadly in horses (80% mortality) but causes death in only about 1% of infected humans. However, in those who actually develop encephalitis the mortality rate goes up to 20%. In a bioweapon attack, human and equine populations would develop the disease at the same time. 

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