Epizootic hemorrhagic disease virus, often abbreviated to EHDV, is a species of the genus Orbivirus, a member of the family Reoviridae. It is the causative agent of epizootic hemorrhagic disease, an acute, infectious, and often fatal disease of wild ruminants. In North America, the most severely affected ruminant is the white-tailed deer (Odocoileus virginianus), although it may also infect mule deer, black-tailed deer, elk, bighorn sheep, and pronghorn antelope. It is often mistakenly referred to as “bluetongue virus” (BTV), another Orbivirus that like EHDV causes the host to develop a characteristic blue tongue due to systemic hemorrhaging and lack of oxygen in the blood. Despite showing clinical similarities, these two viruses are genetically distinct.
Worldwide, eight serotypes of EHDV have been identified. Historically, only serotypes EHDV-1 and EHDV-2 have been found in North America, but recent research has discovered at least one more in the Midwest and Southern United States. EHDV can only be spread by an insect vector. In North America, the common vector is the biting midge (Culicoides variipennis). The first identified outbreak of EHDV in the United States in 1955 caused several hundred white-tailed deer to die in New Jersey and Michigan. Cases of EHDV-like die-offs have been reported prior to 1955 (as far back as 1890), but EHDV was not identified in these cases, as its existence was not yet known.