equine encephalitis (ēˈkwĪn ĕnsĕfˌəlĪˈtĭs) [key], infectious disease of horses caused by any of several viruses, four of which—the Eastern, Western, Venezuelan, and St. Louis viruses—can also infect humans. The viruses, which begin their life cycles as parasites of wild birds, are transferred to horses, and from horses to humans, in the salivary glands of mosquitos. The symptoms of equine encephalitis include fever, drowsiness, and incoordination, often followed by paralysis and death. The mortality rate is 90%, usually within 2 to 3 days, in the most virulent, Eastern type; and as high as 50% in the Western type. The disease, for which no specific treatment is known, can be prevented by annual vaccination of horses. Equine encephalitis is a serious public-health problem in N South America. In 1991 the Eastern virus infected horses throughout much of the SE United States; five infections of humans occurred in Florida. In 1992 the virus was first identified in the Asian tiger mosquito, an aggressive feeder on both horses and humans, now found in some 20 states of the E United States.
See H.-J. Wintzer, Equine Diseases (1986).