It's kind of funny you ask because just 6 months or so I had this question pop up on my PhD Preliminary exam from one of my committee members. Here was response and I back-checked to make sure everything was spot on. Thankfully it was!!! I obviously left out some details, but here was my exam response.
3. Provide a thorough discussion of epizootic hemorrhagic disease (EHD) in white-tailed deer. Your discussion should include, but not be limited to, issues relating to mode of transmission, frequency of occurrence, geographic distribution, immunity, symptoms, probability of survival, and prevention.
EHD is not the exact same thing as blue tongue, though the 2 have very similar symptoms. EHD is a viral infection that is transmitted from tiny midges to white-tailed deer. The disease cannot be spread from an infected white-tailed deer to another, but rather must also be exposed to the biting midges which transmit the disease. EHD usually outbreaks in localized pockets throughout the white-tailed deer's range and outbreaks can be as minor as only a few individuals dying to severe outbreaks in which large portions of a herd may die off. It appears to be cyclic in its nature and does not often hit the exact same area hard year after year, and some believe that years of drought result in greater number of die-offs. Deer are only susceptible to EHD before temperatures cool to frosts in the fall because frosts kill the midge populations. There are 2 basic forms of EHD – an acute and a chronic form. If deer contract an acute infection, death is imminent and usually occurs within 24-48 hours. Death is by massive hemorrhaging of the internal organs and is often diagnosed by lesions on the tongue, liver, and other vital organs. Also, deer usually have a high fever which drives them to water sources – often where they die and are later discovered. Deer often exhibit a “blue” tongue symptom which is indicative of deer having low oxygen flow as hemorrhaging slows blood's ability to distribute oxygen throughout the body; however, the deer's body often appears in good condition because the disease works so fast that no weight loss or other external symptoms have time to develop. The other form of EHD is a chronic variant which deer may often survive. Symptoms are emaciation and a stumbling gait which is usually caused by the sloughing of the deer's hoofs. This phenomenon is often observed by hunter's taking deer in the fall and winter and seeing abnormal hoof growth. Deer that have survived chronic EHD are from then on immune to the disease. EHD is not thought to be spreadable to humans and there is no apparent risk in eating deer that survived chronic EHD. There is no sure prevention, though small efforts have been made to develop oral vaccinations which have been put in pelletized food. High fence operations and captive breeding facilities may spend great amounts of money fumigating midge populations at a regular interval throughout the summer and early autumn months, but I'm not sure how effective this method is in preventing EHD from occurring.
