Eastern Equine Encephalitis

Encephalitis is an acute inflammatory process that primarily involves the brain. The meninges are frequently involved (meningoencephalitis). Eastern equine encephalomyelitis (EEE) is a mosquito borne viral disease of all equine species such as horses, asses, and zebras. After infection, equines may suddenly die or show progressive central nervous system disorders. The rapidity of deterioration and eventual outcome of infection vary among individual horses.

EEE is caused by a virus from the Alphavirus genus, which is part of the antigenically similar family of viruses known as Togaviridae. (Alphaviruses are also responsible for WEE and VEE.) These alphaviruses are spherical and have a diameter of 60-65 nm. The outer layer consists of a glycoprotein shell with protruding glycoprotein spikes found beneath the lipid bilayer. The nucleocapsid core contains the single-stranded RNA genome. The virus that causes EEE is transmitted primarily by mosquitoes that bite an infected animal and then bite and feed on another animal or human. The speed with which the disease spreads depends on the density of mosquito populations.

The incidence of encephalitis is 1 case per 200,000 population in the United States, with herpes simplex virus (HSV) being the most common cause. The arboviruses account for 10% of cases; occasionally, during an epidemic, they can account for as many as 50%. The equine mortality rate due to EEE ranges from 75 to 90 percent.

Treatment

Focus management primarily on supportive and preventive measures. Pharmacologic therapy consists primarily of antipyretics, analgesics, and anticonvulsants. Treatment consists of corticosteroids, anticonvulsants, and supportive measures (treating symptoms)such as intravenous fluids, tracheal intubation, and antipyretics.