(MMWR 1988;37:506-508, 513-515)
IN 1987, 148 U.S. cases of arboviral encephalitis were reported to CDC. Outbreaks of western equine encephalitis (WEE) and St. Louis encephalitis (SLE) in the Great Plains and Mountain states resulted in 41 WEE cases (one fatal) and 17 SLE cases.1 The WEE outbreak led to an epizootic among horses in the same region, producing 173 equine cases. LaCrosse virus, the principal cause of endemic arboviral central nervous system (CNS) infections in the United States, was the etiologic agent in 87 cases (one fatal) reported in 1987. Three sporadic cases of eastern equine encephalitis (EEE) were reported from recognized endemic foci on the Atlantic Coast.
Western equine encephalitis. The WEE outbreak was first recognized in southern Texas with reports of equine cases in April and June. By June, the epizootic had spread through the panhandle of Texas, Oklahoma, New Mexico, and southern Colorado, and by July,