Trending
MIDWEST -- Underway this season is Wisconsin’s worst outbreak of epizootic hemorrhagic disease (EHD), which affects white-tailed deer and other ruminants and is transmitted by biting flies referred to as midges, gnats or no-see-ums.
The viruses that cause the disease do not infect humans, so people “are not at risk when handling infected deer, eating venison from infected deer or being bitten by infected Culicoides midges (no-see-ums),” according to the Wisconsin Department of Natural Resources (WDNR).
The illness causes extensive bleeding and is sometimes fatal in deer. “Clinical signs of EHD are sudden and can be severe. Deer initially lose their appetite and fear of humans, grow progressively weak, become disoriented, may have excessive salivation, and develop a fever. With the high fever that they experience, deer seek out bodies of water to immerse themselves as they attempt to reduce their body temperature,” reports the Michigan Department of Natural Resources (MDNR).
EHD typically occurs in the southern and western states; Wisconsin and Michigan are at the northern edge of its range, though some experts note that it could expand if warmer weather continues in the North. In the South, fewer cases result in fatality because young deer are exposed to the viruses early and continuously.
“Epizootics in northern latitudes are infrequent and are characterized by severe clinical disease and mortality, whereas virus exposure in southern latitudes is more frequent and often results in mild or inapparent disease,” stated a 1997 research paper.
Initial discovery of EHD in North America was in New Jersey in 1955. Michigan also experienced some cases that year, and then went without observing EHD for a few decades. The disease was first was detected in Wisconsin in 2002 when “approximately 14 deer were found suddenly dead in Iowa County,” the WDNR reported.
The disease now only appears sporadically in the region. Studies in 2011 showed that white-tailed deer in Wisconsin did not carry antibodies and were in danger of dying if exposed.
“Over the past two decades, this condition has been responsible for substantial outbreaks in deer in many northern U.S. states and provinces in southern Canada,” notes the MDNR. “Because outbreaks and exposure are inconsistent and patchy, immunity to EHD hasn't developed across the deer herd in Michigan as it has in southern states.”
Technically, there are a couple viruses that can cause hemorrhagic diseases. In Michigan, it’s almost always been EHD.
“The causative agent of EHD is EHDV (Epizootic hemorrhagic disease virus). This virus belongs to the genus Orbivirus within the family Sedoreoviridae, similar to bluetongue virus (BTV) and African horse sickness virus (AHSV),” reads a 2023 report published by the National Library of Medicine. “EHDV and BTV share a variety of domestic and wild ruminant hosts, including sheep, white-tailed deer (WTD), and cattle, although susceptibility to clinical disease associated with these viral infections varies greatly among host species, individuals, and viral serotype.”
Though susceptible, cheep and cows rarely die after contracting EHD.
Outbreaks are short-lived, tending to appear between August and October and ceasing when the midges die during the first frosts.
“What we know about this disease and what we’ve seen from other outbreaks in Wisconsin and in other states is that the impacts from the disease are short-lived, and populations will rebound quickly,” said WDNR Deer Herd health Specialist Erin Larson, as reported by Wisconsin Public Radio. “We definitely, statewide, want to encourage folks to get out and enjoy hunting this fall.”
That comes during a time when over 1,000 white-tailed deer in a southeast portion of state have been infected -- the greatest number during a single year.
In Wisconsin, the current EHD outbreak has been confirmed in wild deer in Washington and Waukesha counties, and suspected cases are also being reported from Dodge, Jefferson, Milwaukee and Ozaukee counties.
In Michigan in 2026, EHD has been identified in the counties of Branch, Hillsdale, Ingham, Jackson, Lapeer, Lenawee, Oakland and Washtenaw.