what is equine encephalomyelitis
equine encephalomyelitis a type of encephalomyelitis in horses and mules, caused by an alphavirus and spread to humans by mosquitoes; it occurs in summer epizootics in the Western Hemisphere. Three forms are recognized: eastern, western, and Venezuelan.quine encephalomyelitis, western a viral disease of horses and mules, communicable to humans, occurring chiefly as a meningoencephalitis with little involvement of the medulla oblongata or spinal cord; observed in the United States chiefly west of the Mississippi River.