Blue Tongue and Epizootic Hemorrhagic Disease (EHD) are viral diseases that impacts farmed and free-ranging white-tailed deer. Though Blue Tongue and EHD are distinctly different, these diseased are sometimes impossible to tell apart. In fact, blood tests results are very similar. For the sake of this article, Blue Tongue and EHD will be used interchangeably. This disease is found most often in sheep, but Blue Tongue has also been found in other livestock such as cattle and goats and other wild ungualtes such as pronghorn antelope and whitetail deer.
White-tailed deer populations have been dealing with these diseases for years, but deer populations continue to hold strong. Blue Tongue and EHD outbreaks in the U.S. occur in deer almost yearly at southern latitudes. EHD and Blue Tongue are spread by midges such as flies or gnats. These insect vectors spread the disease when they bite deer. As a result, outbreaks are virtually untreatable and typically run a course on an annual basis, although weather conditions impact the duration and severity of the outbreak.
Blue Tongue and EHD outbreaks are more noticeable during periods of high temperatures and little rain, but the deer death rate is usually low, with only a small percentage die-off in the population. A deer infected with EHD and Blue Tongue will change its behavior. It will become less careful and seek both shade and water. Some of the symptoms of this deer disease are high fever, excessive salivation, and swelling of the facial area and tongue.
The “blue tongue” that gives the disease its name occurs only in a low number of cases. Symptoms will begin to show within a week after a whitetail deer is bitten and infected with Blue Tongue or EHD virus. Infected whitetail are less fearful of humans, salivate excessively, exhibit peeling or sloughing of the hoof walls, lose their appetite, and do not forage for food. Blue Tongue and EHD induced death can directly come from hemorrhages of the heart or other organs and indirectly from inadequate nutrition/starvation. Hemorrhage and lack of oxygen in the blood results in a blue appearance of the oral mucosa, hence the name “blue tongue.” Blue Tongue and EHD are non-transferable to humans.
In closing, Blue Tongue and EHD are carried by biting insects infected with the disease. Environmental conditions impact the severity of an outbreak and dry periods tend to be the worst. Most episodes are detect during the summer months or drought. Infected deer will often show no fear of humans and often salivate excessively. Eight to 36 hours following the onset of observable signs, deer pass into a shock-like state, become prostrate and die. Whitetail that die from these diseases will often be found in the shade and in or near water sources such as creeks, rivers or tanks.