EQUINE ENCEPHALOMYELITIS (Eastern and Western) SUMMARY Eastern and Western equine encephalomyelitis viruses belong to the genus Alphavirus of the family

Eastern and Western equine encephalomyelitis viruses belong to the genus Alphavirus of the family Togaviridae. Alternate infection of birds and mosquitoes maintain these viruses in nature. The disease occurs sporadically in horses and humans from mid-summer to late autumn. Horses and humans are tangential dead-end hosts. The disease in horses is characterised by fever, anorexia, and severe depression. In severe cases, the disease in horses progresses to hyperexcitability, blindness, ataxia, severe mental depression, recumbency, convulsions, and death. Eastern equine encephalomyelitis (EEE) virus infection in horses is often fatal, while Western equine encephalomyelitis (WEE) virus can cause a subclinical or mild disease with less than 30% mortality. EEE and WEE have been reported to cause disease in poultry, game birds and ratites. Sporadic cases of EEE have been reported in cows, sheep, pigs, deer, and dogs.