Outbreak of viral deer disease linked to mass deer deaths reported in southwest Michigan

ST. JOSEPH COUNTY, Mich. — A common viral disease that can cause mass deer deaths locally has been identified in southwest Michigan, and early reports suggest some deer populations could see a “significant outbreak” as soon as 2024, according to state wildlife officials.

The Michigan Department of Natural Resources Epidemic hemorrhagic diseaseOfficials announced Friday, Sept. 6, that a wild white-tailed deer (EHD) had been found in St. Joseph County south of Kalamazoo, ending a three-year hiatus on EHD in the county.

The DNR has also received reports of more than 120 suspected cases of EHD in the past few weeks, mostly from counties in the southwest Lower Peninsula, some of which are awaiting laboratory confirmation, officials said.

Michigan has seen sporadic deer deaths from the disease since 2006, with an estimated 50 to 1,000 deer killed in isolated areas, with the largest death toll occurring in 2012, when approximately 14,000 deer died in more than 30 counties.

“You can have a disease outbreak in one square mile that is having a major impact on a deer population while a few miles away you can see nothing happening,” said Chad Stewart, acting superintendent of the DNR's Division of Wildlife Sustainable Population Management.

“That being said, there are many more locations where the disease is occurring this year, with a particular concentration in the South West,” he added.

EHD is transmitted by blood-sucking flies of the Culicoides genus, and the DNR says weather conditions in 2024 have made it more likely to spread. Studies in other states have shown that a warm spring followed by a relatively rainy July and a hot, dry August is a major factor in creating more muddy areas where flies can lay their eggs, making outbreaks more likely.

Officials say there is no evidence that humans or household pets can become infected with the EHD virus, and while venison harvested in areas affected by EHD is still safe to eat, the DNR recommends that hunters avoid eating meat from visibly sick deer.

Stewart said more information will allow the department to better understand the distribution and impact of the virus, and the DNR is asking residents to report any suspected deer deaths due to EHD.

Sick and dead deer are often found in or near water because the virus causes high fevers and dehydration in deer, which can lead them to flee for water. As the disease progresses, deer lose their appetite, become fearful of humans, become gradually weaker, salivate excessively and eventually lose consciousness, according to the DNR.

“Hunter observations are especially helpful when you're out in the fields this fall and looking around,” Stewart said. Anyone who spots a sick or dead deer near water can report it to the DNR. Eyes in the Field webpage.

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Mortality rates can be high in some areas, but not all deer will get EHD and not all infected deer will die, Stewart said. It is not transmitted from deer to deer.

“Deer that survive epizootic hemorrhagic disease develop immunity to the virus, and successive outbreaks are rarely seen in the same area,” he said.

There are no known effective treatments or control methods for EHD in wild populations, and the disease has been observed in many parts of the United States for decades.

Deer carcasses can be disposed of through natural decomposition and do not spread EHD or contribute to the spread of infection. If owners want to remove the carcass, they are responsible for its disposal and can either bury it or dispose of it in a landfill that accepts household waste, officials said.

Wildlife officials expect more counties to confirm cases of EHD over the next few weeks through lab testing within 24 hours of death. If the presence of the disease is confirmed, there is no need to further test deer in those counties, according to the DNR.

Areas where cases have been reported since early August are expected to have the most widespread population impacts, while areas where no cases have been reported until mid- to late September are likely to be less severely affected.

The onset of hard frosts will likely kill off the flies that carry the virus, halting its spread, Stewart said.