Epizootic Hemorrhagic Disease
The weather is so beautiful that you decide to take a hike along a stream or small river and you come across a deceased white-tailed deer in or around the water. Unfortunately, it is not an uncommon scenario. Epizootic hemorrhagic disease or EHD is a viral disease of white-tailed and mule deer that is spread by biting gnats. Domestic ruminants such as cattle and sheep are typically asymptomatic carriers of the virus but occasionally cattle will exhibit clinical disease.
In warm dry weather gnats and deer congregate near watering holes. These gnats are actually of the Culicoides species, which are biting flies, or midges. The virus is not transmitted directly between deer but rather through the Culicoides species which pick up the virus from one deer and inoculates the virus into another.
The spread of the disease can be stopped by the first frost which will kill the disease-carrying gnats. It also tends to spread the deer over a wider geographical area, thereby limiting their exposure to the virus.
The incubation period for the virus is five to ten days. The first signs of disease may include disorientation, lameness or unresponsive behavior to the presence of humans. These animals are lethargic and may have a bloody discharge from their nose; they often develop lesions or sores on the mouth, salivate excessively, and may develop a swollen, blue tongue. The deer may appear emaciated because they will stop eating and even drinking, although they congregate near water. Eight to 36 hours following the onset of clinical signs, deer pass into a shock-like state, become prostrate, and die.
The morbidity of EHD can reach a 90% level with a mortality rate of around 60%. making this Orbivirus one of the most important viral diseases of deer.
The disease may be confirmed through viral isolation or serologic monitoring.
Radostits, Otto, and Clive Gay. Veterinary Medicine. 10th Edition. P. 1305.