Hemorrhagic Disease in Deer

by Amanda Dougherty, photos courtesy QDMA

Outbreaks of hemorrhagic disease in white-tailed deer and mule deer date back to as early as 1886 and 1901 in the Western US. The cause of the hemorrhagic diseases was identified as a virus in the 1950’s. Two separate viruses, epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) are referred to collectively as hemorrhagic disease (HD). HD has only been associated with significant wild animal death in North American populations. This disease has been reported in numerous states, generally located in a wide diagonal band from the southeast corner of the US to the northwestern corner, including California. In Canada, HD has been reported in wild animals in the southern portions of British Columbia, Alberta and Saskatchewan. Hemorrhagic disease primarily affects white-tailed deer and mule deer, but mortality has been reported in pronghorn. Clinical disease also has been reported in desert bighorn sheep. These viruses are spread by a vector, Culicoides spp. or biting midges, of which several different species are known to transmit the viruses. Outbreaks of HD occur during the late summer and early fall which relates to the seasonal activity of the midges. Frequency of reports varies and outbreaks can be sporadic. More Northern areas (higher latitudes) equal fewer reports of outbreaks but have higher rates of mortality, whereas southern regions experience frequent outbreaks but rarely report mortality. This observation indicates that there may be some acquired immunity to the viruses in deer, differences in severity of disease due to changes in the viruses, or changes in vector activity.

The signs of hemorrhagic disease in deer can range from sudden death to chronic disease. Infection with the viruses does not always result in disease and nonfatal infections may occur. Sick and dead animals are generally found near water. Signs in white-tailed deer can range from swelling of the face, eyes, and neck, anorexia, lethargy, weakness, in-coordination, excessive salivation, blood tinged saliva, bloody diarrhea, lameness, hemorrhages of the skin and on the coronary band of the hoof, ulcers in the mouth, and respiratory distress. The disease normally progresses from face and neck swelling to lameness, then hemorrhage, and finally mouth ulcers. Animals that have survived the disease often exhibit cracked hooves. The clinical signs are important because they resemble foreign animal diseases which would have severe consequences for domestic livestock, like foot and mouth disease, which are not currently found in the United States. Sheep and cattle are susceptible to HD with varying levels of disease effects. There is no human health threat from either one of the viruses known to cause hemorrhagic disease.
Currently, there is no wildlife management tool or strategy to prevent, predict, or minimize impacts of this disease. However, HD is considered the most important viral disease affecting white-tailed deer in the US. There are many reports of high mortality related to HD, and it has been suggested that high disease mortality combined with normal hunting kill can result in long-term population declines. The role of overpopulation and the spread of HD is not fully understood. It has been suggested that climate change and the spread of the biting midge vector, along with changes in the viruses will mean future outbreaks in areas where the disease has not been previously. Spread of the disease is certainly a consideration for wildlife management and setting of hunting seasons to ensure robust and healthy deer populations. If you encounter any animals with these signs, you are encouraged to contact your state’s game agency.