A virus spread by tiny biting midges is suspected in more than 1,800 deer deaths in southeastern Wisconsin, and has now been detected in a dairy herd.
An outbreak of epizootic hemorrhagic disease (EHD) is affecting wild white-tailed deer in southeastern Wisconsin. As of September 28, 2026, the Wisconsin Department of Natural Resources (DNR) had confirmed the disease in Washington and Waukesha counties and was tracking reports of suspected EHD deaths in 5 additional counties. Washington County has been hit the hardest, with just over 1,200 suspected deaths.1
EHD virus has also been detected in livestock. On September 29, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) announced that samples from non-lactating dairy cattle in Waukesha County had tested positive for the virus that causes EHD. The agency also said EHD had been detected in tissue from wild and captive deer in the region.2
EHD is a viral disease spread by Culicoides biting midges, often called no-see-ums. According to the DNR, the clinical signs of EHD and bluetongue are "virtually indistinguishable." The 2 conditions are caused by different viruses: epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV).1
Outbreaks follow the 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," the DNR states.1
Affected deer may show "excessive salivation, foaming around the nose and mouth and appearing weak or approachable by humans," according to the agency. Deer can develop very high fevers, so carcasses are often found in or near water.1
The DNR says the virus does not survive in carcasses. Agency staff cannot collect or remove deer suspected to have died from EHD. Residents who need to move a carcass are advised to wear basic protective equipment, such as gloves, and practice good hygiene.1
EHD was first diagnosed in Wisconsin in fall 2002, when 14 deer in Iowa County died of the disease. Blood samples collected from 2002 to 2011 showed that Wisconsin deer generally lacked antibodies to hemorrhagic disease viruses, which suggests they had little routine exposure.1
Wisconsin Public Radio reported that the state's largest previous outbreak, in Crawford County in 2019, produced reports of up to 226 suspected EHD deaths, and prior to that, a 2012 outbreak produced up to 132 reports of dead deer.3 In August, when the DNR had received just over 100 reports, Erin Larson, DNR deer herd health specialist, told the outlet she expected this year's outbreak to come close to or pass the 2019 total.3
The DNR notes that death rates in Wisconsin "can be much higher" than in regions where deer encounter hemorrhagic disease viruses more often.1 Even so, the agency cites research showing that affected populations will likely "quickly rebound due to natural recruitment" after local declines.1 "Often there's really no long-term impacts to the deer herd," Larson told Wisconsin Public Radio.3
Wisconsin is not the only state reporting hemorrhagic disease this season. On September 9, the Michigan DNR confirmed the state's first 2026 cases of EHD in deer from Branch, Ingham, Jackson, and Lenawee counties.4 "The impacts of EHD on northern states seems to be changing," Scott Larsen, a veterinarian with the Michigan DNR Wildlife Division, said in the agency's release.4
EHD has also been detected in Pennsylvania deer this season, with the Pennsylvania Game Commission confirming an outbreak in Chester County.5,6 Missouri's Department of Conservation is tracking hemorrhagic disease reports across dozens of counties in 2026.7
Both viruses that cause hemorrhagic disease—EHDV and BTV—have been reported throughout the US except a handful of New England states, according to the Southeastern Cooperative Wildlife Disease Study (SCWDS) at the University of Georgia. SCWDS notes that outbreaks are less common in the upper Midwest and Northeast but are becoming more frequent there.8 A 2021 analysis of a large 2017 outbreak across the eastern United States also described "a northern expansion of HD" in Midwestern and Northeastern states "where outbreaks were historically rare."9
DATCP says cattle rarely show signs of EHD. When they do, signs can include lameness, sores on the limbs, mouth, or teats, excess salivation, fever, or weight loss.2 The agency noted that oral, teat, or hoof lesions can resemble foreign animal diseases. Suspected foreign animal disease cases should be reported immediately to a DATCP district veterinarian.2
EHD is reportable in Wisconsin, and cases must be reported to DATCP within 10 days. DATCP encouraged herd owners to work with their veterinarians on diagnosis. Blood, spleen, lung, or lymph node samples can be submitted for laboratory testing to differentiate EHD from other diseases with similar symptoms.2
There is no treatment for EHD. DATCP recommends supporting overall herd health through parasite control, proper nutrition, and avoiding overcrowding.2 The state last documented EHD in cattle in 2013.2
Both Wisconsin agencies say EHD does not infect humans. According to the DNR, people are not at risk even if they handle deer suspected of having EHD, eat venison from infected deer, or are bitten by infected midges.1 "There is no evidence that EHD infects humans," DATCP said in its release, adding that people are not at risk from insect bites or from meat or milk from affected animals.2
The DNR asks the public to report sick or dead deer through its online Sick/Dead Wildlife Reporting Form, by email at DNRWildlifeSwitchboard@wisconsin.gov, or by phone at 608-267-0866.1
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