This 1975 transmission electron micrograph (TEM) revealed the presence of a number of Eastern Equine Encephalitis (EEE) virus virions that happened to be in a specimen of central nervous system tissue. EEE is an zoonotic arbovirus, which means that its spead to human beings through the bite of an infected mosquito. EEE virus (EEEV) occurs in the eastern half of the United States where it causes disease in humans, horses, and some bird species. Because of the high mortality rate, EEE is regarded as one of the most serious mosquito-borne diseases in the United States. EEE is a Togaviridae virus family member, and the genus Alphavirus.