Epizootic hemorrhagic disease, or EHD, is often deadly for white-tailed deer. But it’s harmless to humans and most other animals.
So far this year, the Michigan Department of Natural Resources has received reports of about 4,000 deer that have died of EHD, most from southwest Michigan.
"That's probably going to be a minimum number," said Chad Fedewa, acting Deer, Elk, and Moose Management Specialist at the Michigan DNR. "Obviously, not all deer are found, and not all deer that are found are going to be reported."
He said, "to put, kind of, that number into perspective a little bit. St. Joseph County, for example, the last couple of years have reported about three to four thousand deer are harvested each year during the hunting season."
Population effects from EHD are much more localized than from hunting, however, meaning individual herds may be heavily impacted.
The disease is spread by biting flies that thrive in wet, muddy environments. Infections of EHD thus cluster around those areas.
Sonja Christensen researches wildlife diseases at Michigan State University. She explained, "One landowner or farmer or hunter might see a regular healthy deer population and not notice the difference at all this year."
But, Christensen said, "five miles down the road, near a wetland or a river corridor, that farmer or hunter or landowner might see a lot of dead deer near waterways, or just many fewer deer walking around the woods this time of year."
EHD's impacts on local populations can be significant. But Christensen said she expects herds to recover within three to five years.
This year’s EHD season is now coming to a close. That's because the biting flies, or midges, that spread the disease are affected by the change of season.
"Whenever we see these cooler temperatures, that slows down everything," said Christensen. "It slows down the life cycle of the midge. It slows down even the ability of the virus within the midge to replicate. So cooler temperatures generally means less transmission and less midge activity."