Epizootic hemorrhagic disease

Epizootic hemorrhagic disease (EHD) is a hemorrhagic disease of white-tailed deer (Odocoileus virginianus) caused by an infection of a virus from the genus Orbivirus (Shope et al. 1960, Howarth et al. 2001). It is an infectious, and sometimes fatal, virus that is characterized by extensive hemorrhages, and is found throughout the United States. It is important for deer hunters, farmers, farm property owners, and livestock owners to have knowledge about EHD because of the seriousness of this disease, its ability to cause large scale outbreaks in wild ruminants, and its ability to affect livestock and the production industry. Epizootic hemorrhagic disease has been found in some domestic ruminants and many species of deer including white-tailed deer, mule deer, and pronghorn antelope. Seropositive black-tailed deer, fallow deer, red deer, wapiti, and roe deer have also been found, which essentially means that they were exposed to the disease at some time in the past, but may not be involved in transmission. Outbreaks of EHD have been reported in cattle although it is rare for them to develop disease or die. Sheep may develop clinical signs; however, this is also rare (Howarth et al. 2001). Epizootic hemorrhagic disease is often called bluetongue; however, this is incorrect. Bluetongue virus is closely related to EHD, and has similar clinical signs, but it is a different disease. Bluetongue is a serious disease in cattle, as well as other ruminants, and can have a significant effect on international trade. Testing at animal health laboratories is necessary to distinguish between the viruses that cause bluetongue and EHD.

EHD was first reported in 1955 in New Jersey, killing 700 whitetails. In Alberta in 1962, EHD killed 440 whitetails, 18 mule deer, and 13 pronghorn. In a 1976 outbreak, thousands of whitetails died from EHD in Nebraska, Wyoming, Kansas, and the Dakotas, and 4000 antelope died in Wyoming. Another 1000 whitetails died from EHD in New Jersey in 1976.

The distribution of EHD depends greatly on the distribution and abundance of the biting midge (Culicoides variipennis), the level of existing immunity in deer, and the genetic variations in susceptibility. Epizootic hemorrhagic disease is found in North America, Australia, Asia, and Africa. Seropositive animals have also been found in South America. Epizootic hemorrhagic disease is known to occur most often in the southern United States, although its distribution is not uniform. In the south, the disease is characterized as frequent and mild, whereas in the north, the disease is characterized as infrequent, severe, and capable of high mortality (Gaydos et al. 2004). Epizootic hemorrhagic disease can occur throughout Indiana. Outbreaks in Indiana of the disease can be characterized by both significant outbreaks that occur on a 5-10 year cycle that affect the entire state and smaller outbreaks that may only involve a few counties.

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