EHD, or epizootic hemorrhagic disease, is a viral illness that attacks the blood vessels of white-tailed deer, causing internal bleeding, high fever, and often rapid death within 8 to 36 hours of symptoms appearing. It is the most significant viral disease of deer in the southeastern United States and increasingly affects herds farther north. The virus cannot infect humans.
How Deer Get Infected
EHD spreads through the bite of tiny flying insects called Culicoides midges, sometimes known as no-see-ums, sand gnats, or punkies. These midges pick up the virus by feeding on an infected animal, then pass it along when they bite the next deer. There is no deer-to-deer transmission. You won’t see one deer catch it from another through contact or shared food sources.
Cases appear from late July through November, when midges are most active. Drought conditions concentrate both deer and midges around shrinking water sources, creating the perfect setup for outbreaks. The first hard frost of fall kills the midges and effectively ends the transmission season each year.
What Happens Inside an Infected Deer
The virus belongs to a family called Orbivirus, and it targets the walls of small blood vessels throughout the body. It damages and destroys those vessel walls, triggering widespread inflammation, clotting within the vessels, and bleeding into surrounding tissues. Organs farther from the heart lose their oxygen supply first, which is why extremities like hooves and the muzzle show some of the earliest and most visible damage.
After a midge bite, the incubation period ranges from about 5 to 10 days, with symptoms typically beginning around day 7. Once clinical signs appear, the disease can kill a deer in as little as 8 hours, though some survive up to 36 hours. This speed is part of what makes EHD so alarming to hunters and wildlife managers who discover multiple dead deer in a short window.
Visible Signs of EHD
Infected deer develop a high fever, which drives one of the most recognizable behaviors: they seek out water. Many deer that die of EHD are found in or near ponds, creeks, and rivers. Other signs include:
- Swelling of the head, neck, tongue, and lips
- Drooling and a runny nose
- Hemorrhaging in muscles and internal organs
- Ulcers and bleeding in and around the mouth
- Lameness from pain and redness where the skin meets the hoof wall
- Blue-tinged tongue from lack of oxygen (a sign shared with the related bluetongue virus)
Deer that survive the acute phase sometimes develop chronic hoof problems. The interrupted blood supply to the hooves during infection can cause the outer hoof wall to crack or slough off weeks later, leaving the animal lame for an extended period.
EHD vs. Bluetongue
Bluetongue virus and EHD virus are closely related, spread by the same midges, and produce nearly identical symptoms. Even lab testing is sometimes needed to tell them apart. The practical difference is which species they hit hardest. EHD is primarily a deer disease, affecting all ages and often causing mass die-offs in white-tailed deer. Bluetongue tends to be most severe in sheep, while cattle exposed to either virus typically experience milder illness or reproductive losses rather than death.
Three serotypes of EHDV (1, 2, and 6) currently circulate in North America. Some serotype 6 viruses are actually genetic hybrids between serotype 2 and serotype 6, a reshuffling that can complicate immunity in deer that survived a previous outbreak.
Where EHD Occurs
EHD has historically been concentrated in the southeastern U.S., where warm seasons are long and midge populations thrive. Over the last two decades, though, the disease has expanded noticeably northward. States in the Midwest and Northeast that rarely reported cases are now seeing outbreaks. Within individual states like Illinois, researchers have documented a clear shift in reported cases toward higher latitudes over a 38-year study period. Warmer temperatures extending the midge season and expanding their range are a likely driver.
Impact on Local Deer Populations
An EHD outbreak can be devastating at the local level. Hunters may find dozens of dead deer along a single stretch of creek, and a hard-hit area can lose a significant portion of its herd in one season. Wildlife agencies sometimes reduce hunting permits in affected zones the following year to help populations recover.
The good news is that deer populations are resilient breeders. According to the Ohio Department of Natural Resources, herds in affected areas usually bounce back within a few years. Deer that survive an infection also develop some immunity to the specific serotype they encountered, though they remain vulnerable to other serotypes.
Is EHD Dangerous to Humans?
No. EHD viruses do not infect people. You face no risk from handling an infected deer, being bitten by a Culicoides midge that carries the virus, or eating venison from a deer that was exposed. That said, deer with obvious signs of advanced, body-wide disease are not considered suitable for consumption, simply because the meat quality has deteriorated from hemorrhaging and tissue damage. A healthy-looking deer harvested during hunting season that happened to carry the virus poses no food safety concern.
What Hunters and Landowners Can Watch For
The clearest red flag is finding dead deer near water during late summer or early fall, especially during a drought year. Multiple carcasses along a pond or creek bank in a short timeframe strongly suggest EHD rather than predation, poaching, or other causes. If you find deer that appear to have died suddenly near water, reporting the location and approximate number to your state wildlife agency helps biologists track outbreaks and adjust management plans. Most states have online reporting tools or hotlines specifically for this purpose.
There is no vaccine or treatment available for wild deer. Management strategies focus on monitoring outbreaks, adjusting harvest quotas afterward, and maintaining quality habitat so populations can rebound. Because the midge vector is nearly impossible to control across a landscape, EHD remains a natural cycle that deer herds have coexisted with for centuries, even as its geographic footprint continues to shift.