Nik Rajkovic / news@whmi.com

A common viral deer disease has made a return to St. Joseph County after a three-year hiatus, with additional counties likely to follow. Over the past several weeks, the Michigan Department of Natural Resources has received reports of over 120 probable cases of epizootic hemorrhagic disease, primarily from counties in the southwestern Lower Peninsula.

The DNR Wildlife Health Section and the Michigan State University Veterinary Diagnostic Laboratory recently confirmed the EHD virus in a free-ranging white-tailed deer from St. Joseph County. Several other counties are awaiting lab confirmation.

EHD is a viral, sometimes fatal disease found in wild ruminants such as white-tailed deer, mule deer and elk.

“Although early reports indicate 2024 could see a significant outbreak of epizootic hemorrhagic disease in pockets of Michigan’s deer population, this isn’t necessarily unusual,” said Chad Stewart, acting supervisor of the DNR Wildlife Division's Sustainable Populations Section.

Stewart said that EHD-related deer deaths have occurred on and off in Michigan since 2006. During these EHD outbreaks, an estimated 50 to 1,000 deer died in isolated areas. The largest die-off occurred in 2012, with an estimated loss of more than 14,000 deer in more than 30 counties. No cases of EHD were confirmed in 2014 or 2015, and deer mortality has occurred to varying degrees annually since 2015.

There is no known effective treatment for, or control of, EHD in wild populations. The disease has been seen for decades in many areas of the United States.

EHD is transmitted by a type of biting fly called a midge of the genus Culicoides. Weather conditions in 2024 have made it easier for the virus to spread. Studies in other states have shown that a warm spring followed by a relatively rainy July and hot, dry August seem to be significant factors that make an outbreak more likely. When these conditions are present, muddy areas where this fly lays its eggs and reproduces become more common. Warm temperatures in late summer and early fall also contribute to the virus replicating more rapidly.

Outbreaks of EHD are characterized in several ways:

• Sick and dead deer are found in or around bodies of water.
• Illness in deer can come on suddenly and severely but also can linger for weeks or months in a low-grade state.
• In severe forms of the disease, deer lose their appetite and their fear of humans, grow progressively weaker, salivate excessively and finally become unconscious.
• Due to a high fever and dehydration, infected deer often seek water to lower their body temperature and to rehydrate.

Stewart said that while mortality rates can be high in some localized areas, not all deer will contract EHD, and not all deer that get EHD will die from it.

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

EHD is not expected to have widespread deer population-level impacts, but it can significantly affect localized areas if mortality is severe. The onset of a hard frost will kill the “insect vector” – essentially the carrier for disease transmission – stopping movement of the virus.

In areas with significant mortality, local deer numbers tend to rebound after two to three years.

EHD is not transmitted from deer to deer. There is no evidence that humans or household pets can contract the EHD virus.

For hunters who hunt in areas that were affected by EHD, venison is still safe for consumption. While it’s not recommended you consume venison from animals that are visibly sick, if a deer is harvested during the hunting season in an area that had EHD, there is no evidence humans can contract the virus from consuming venison.

Deer carcasses can be disposed of through natural decomposition, which does not spread EHD or contribute to outbreaks. Property owners are responsible for proper disposal of carcasses if they wish to remove them. Carcasses can be buried at sufficient depth so that no body parts are showing, or they can be disposed of at landfills that accept household solid waste.

The DNR expects additional EHD cases in more counties to be confirmed in the coming weeks. Deer must be tested within 24 hours of death for proper diagnostic testing, and the whole carcass is required for testing.

Once EHD has been confirmed in a county, no additional deer from that county need to be tested. Areas that have been reporting cases since early August will see the most widespread population impacts. Areas with no reported cases until mid- to late September likely will see less severe effects on local deer numbers.

“If you suspect a deer death is due to epizootic hemorrhagic disease, please report it to the DNR so that we can track cases and better estimate the total number of deer affected in an area,” Stewart said. “Hunters’ observations can be especially helpful as they hit the field and look around this fall.”

Anyone who discovers sick or dead deer near bodies of water is urged to report it using the DNR’s Eyes in the Field webpage below.

Learn more about epizootic hemorrhagic disease in white-tailed deer linked below.