A form of arboviral encephalitis (primarily affecting equines) endemic to eastern regions of North America. The causative organism (ENCEPHALOMYELITIS VIRUS, EASTERN EQUINE) may be transmitted to humans via the bite of AEDES mosquitoes. Clinical manifestations include the acute onset of fever, HEADACHE, altered mentation, and SEIZURES followed by coma. The condition is fatal in up to 50% of cases. Recovery may be marked by residual neurologic deficits and EPILEPSY. (From Joynt, Clinical Neurology, 1996, Ch26, pp9-10).