Wildlife Habitat_Content Page_Disease Epizootic hemorrhagic disease (EHD) in WI deer

Epizootic hemorrhagic disease (EHD) in Wisconsin deer

In the fall of 2024, the epizootic hemorrhagic disease (EHD) virus was confirmed in deer in Chippewa, Jackson, Monroe and Waukesha counties. The number of deer suspected of dying from EHD in these areas remains low.

Deer suspected of dying from EHD and reported to the DNR were sampled and tested from Barron, Brown, Columbia, Jefferson, La Crosse, Pierce, Polk, Shawano, St. Croix and Wood counties. These deer were all negative for EHD. A couple of these deer had evidence of pneumonia. Recent cold and snowy weather throughout Wisconsin has likely killed off the midges that transmit the virus.

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, death rates are lower, usually less than 25% of the population. In areas where the disease rarely occurs, like in Wisconsin, death rates can be much higher. High-density deer herds may have higher mortality rates.

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. Sporadic outbreaks of epizootic hemorrhagic disease occur in Wisconsin. In the fall of 2012, deer found dead in eight southern Wisconsin counties tested positive for EHDV. In the fall of 2019, EHDV was detected in deer found dead in southwestern Wisconsin. In the fall of 2020, there were small outbreaks of less than 50 deer each in Oconto and Buffalo counties and in the fall of 2021, small outbreaks of less than 20 deer each in La Crosse and Juneau counties.

Department staff continues to monitor the deer herd for indications of HD and ask citizens to report any unusual observations of dead deer to the DNR Wildlife Switchboard by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You must leave a message for the switchboard staff to return your call. In your message, please include the number of deer, if they were sick or dead, the specific location where you saw them, including the county and your contact information.

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