What is EHD?

This dead-head was found at Big Oaks, it is suspected to have died from EHD. BOCS Photo

Hemorrhagic Disease (HD) is caused by one of two viruses, epizootic hemorrhagic disease (EHD) virus or blue-tongue (BT) virus. Although the two viruses have non-distinguishable symptoms, they differ genetically. HD is a viral disease that infects all ungulates, most commonly White-Tailed Deer, as well as cattle and domestic sheep. In Indiana, the disease was first detected in the 1890s as a livestock disease, and has since transmitted to White-Tailed Deer and been a common recurrence in our deer populations. Mortality rates of outbreaks are typically around 25%, but more severe outbreaks can wipe out up to 75% or more of a population. The distribution and severity of EHD remains highly variable and unpredictable. 

HD virus is transmitted through the bite of culicoides midges, commonly called “no-see-ums” or black gnats. These midges hatch in stagnant pools of water, starting in August and continuing until the first frost. The seasonality of EHD is the result of this annual hatch. 

Symptoms vary depending on the severity of the infection and the strength of a deer’s immune system. Infection might present as a fever, swollen tongue, or drowsiness in a less severe case, whereas a deer experiencing more severe symptoms might have hemorrhaging or congestion in the heart and other internal organs. Growth interruptions are a sign of extreme fever and can be observed as splitting/peeling of the hoof walls. The fever and congestion of internal organs lead to increased fatigue and respiratory distress; infected deer seek out water and shade in an attempt to cool down in severe cases. HD viruses cannot be transmitted to humans, and meat from an infected or previously infected deer is considered safe to eat. 

Big Oaks has seen a number of EHD outbreaks throughout the years, 2019 being the latest outbreak outside of this current year. An outbreak in 2009 saw the lowest hunter success rates before this season, which is shaping out to be the worst the refuge has seen. A non EHD year success rate would typically be between 15-20% during firearms season; we predict that the success rate for 2025 will be somewhere around 7%. Outbreaks typically occur every 5-8 years and have varying mortality rates, otherwise the disease is mostly unpredictable.

The splitting/peeling of these hoof walls is a textbook example of disruptive growth as a result of extreme fever due to EHD. USFWS Photo 

This dead-head found at Big Oaks has broken and spongy antlers, a sign that this buck died before his antlers were done growing. USFWS Photo  

Should you find a deer at Big Oaks that you suspect to be infected, please record the coordinates and report the finding to refuge staff upon checkout. Should you find a deer elsewhere in Indiana that you suspect to be infected, report the finding to the DNR via their Sick Animal Reporting Form.