Eastern Equine Encephalitis (EEE)

Eastern Equine Encephalitis (EEE) is an arbovirus (arthropod-borne virus) of significance to the equine population. EEE, along with WEE, and VEE, are alphaviruses in the family Togaviridae. In the United States, EEE has historically occurred in all states east of the Mississippi River with particular prevalence in the Southeastern United States. Recently, cases have been identified as far west as Texas and north into eastern Canada. Mosquito vectors for EEE include Aedes spp., Coquilettidia perturbans, and Culiseta melanura.

Mortality can exceed 90% in naive horses and is lower in horses with partial protection or previous vaccination. Death usually occurs within 2-3 days of onset of signs. Horses that survive may have permanent neurologic deficits including abnormal mentation and/or residual ataxia.