Eastern equine encephalitis virus (EEEV) is a member of the genus Alphavirus, family Togaviridae. Other medically important alphaviruses found in the Americas include, Venezuelan equine encephalitis virus (VEEV), chikungunya virus (CHIKV), Mayaro virus (MAYV), and Madariaga (MADV). EEEV has a single-stranded, positive-sense RNA genome. The virus particles are spherical and have a diameter of 60-65 nm. Of the four lineages of EEE antigenic complex, Group I consists of only EEEV and is endemic in North America and the Caribbean and causes most human disease cases. The other three groups (IIA, IIB, and III) are caused by related MADV (formerly known as South American EEEV) and cause primarily equine illness in Central and South America.