Epizootic hemorrhagic disease (EHD) in Wisconsin deer

Hemorrhagic disease (HD) is an acute, infectious, often fatal, viral disease that affects white-tailed deer and other hoofed animals. It is caused by either the bluetongue virus (BTV) or the epizootic hemorrhagic disease virus (EHDV). In areas where HD regularly occurs, such as the southern and western United States, death rates are lower (usually less than 25% of the population) compared to areas where the disease rarely occurs. In Wisconsin, death rates can be much higher, as deer populations have limited previous exposure to the virus and high-density deer herds may have higher mortality rates.

Quick Facts

• Clinical signs of EHD in deer may include excessive salivation, foaming around the nose and mouth and appearing weak or approachable by humans. Carcasses found in or near water sources may also be a sign, as infected deer become feverish and will often lay in water to cool down or drink.
• The EHD virus is spread by midges, which are small flies also known as biting gnats or no-see-ums. The virus does not infect humans, even if a person handles infected deer, eats venison from infected deer or is bitten by infected midges.
• Outbreaks are typically seen between the months of August-October and subside in late fall when the midges that transmit the disease die with the first hard frost. 
• While localized deer populations may experience an immediate decline due to the current EHD outbreak, research shows it is likely affected deer populations will quickly rebound due to natural recruitment. 
• The EHD virus does not survive in carcasses, and DNR staff cannot collect or remove deer that are suspected to have died from EHD. When possible, the DNR advises against handling found-dead wildlife carcasses, as other harmful pathogens could be present. If it is necessary to move or dispose of the carcass of a wild animal, be sure to use basic protective equipment (such as gloves) and follow good hygiene practices.
• Domestic cattle can get EHD, though signs of disease are often absent or minimal. The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) confirmed that samples collected from dairy cattle in Waukesha County tested positive for EHD in September 2026.
• Department staff continues to monitor the deer herd for indications of EHD and ask members of the public to report any unusual observations of dead deer to the DNR Wildlife Switchboard through the Sick/Dead Wildlife Reporting Form or by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866.
• For questions about changing harvest authorizations for the 2026 deer hunting seasons, contact Wisconsin DNR Customer Service at 1-888-936-7463. Please note, changes to harvest authorizations may not be available after the start of the deer hunting season.

History in Wisconsin

The disease was diagnosed for the first time in Wisconsin deer in the fall of 2002 when approximately 14 deer were found suddenly dead in Iowa County. Between 2002 and 2011, blood samples from deer were collected and tested. The results did not find antibodies to the viruses that cause HD, which suggests that deer in Wisconsin are not routinely exposed to these viruses. There have been sporadic events documented since that time, generally with minimal localized impacts on deer.

Below is a list of years and counties where EHD has been confirmed, along with an estimated number of deer in a county suspected of dying from EHD. The estimates are based on citizen and biologist reports of sick or dead deer found with signs consistent with EHD.

Transmission

The viruses are transmitted by biting flies (Culicoides sp.), often referred to as no-see-ums or midges. The virus does not survive long outside the insect or the deer host. Hemorrhagic disease generally affects deer in the late summer and fall, when the biting flies are most abundant. Outbreaks of this disease end after the first hard frost, when insect populations fall.

Clinical Signs

Visible signs of hemorrhagic disease are virtually indistinguishable between the two viruses (BTV and EHDV) that cause the disease. Deer can display multiple symptoms depending on how long they are infected. Deer that are infected and have the most severe cases of the disease may be unafraid of humans, salivate excessively, have foam present around the nose (sometimes with blood), appear weak but in good body condition and may appear to have swollen areas of their body (typically the areas of the head and neck). Deer may also be found in or near water, as they can develop very high fevers and be dehydrated.

In Wisconsin, the disease is detected only when groups of deer are found dead, usually near water sources, and otherwise appear to be in good body condition. In some instances of the more chronic form of the disease, deer may have erosions or ulcerations in their mouth, be very thin and have a detachment of the wall of their hoof, making it difficult for them to walk. In deer that recover, abnormal hoof growth may be noted.

Disease Management

Wisconsin is on the far northern edge of the home range of the flies that carry the virus and so far only has sporadic outbreaks of this disease. If Wisconsin’s overall temperatures increase, it could allow the insects to expand their range farther northward and Wisconsin could see more outbreaks of this disease in the future.

Public Health

The viruses that cause hemorrhagic disease do not infect humans. Therefore, humans are not at risk when handling infected deer, eating venison from infected deer or being bitten by infected Culicoides midges (no-see-ums).

Additional Information

• Southeastern Cooperative Wildlife Disease Study: Hemorrhagic Disease of White-tailed Deer brochure
• Michigan DNR: Epizootic hemorrhagic disease