Recent Deer Deaths in Washtenaw County Attributed to EHD, Not CWD
October 18, 2025
Doug Marrin
Concerns have arisen among Washtenaw County residents following reports of multiple deer deaths, with some fearing the presence of chronic wasting disease (CWD). However, according to the Michigan Department of Natural Resources (DNR), these mortalities are most likely caused by epizootic hemorrhagic disease (EHD), a viral infection distinct from CWD.
Habitat and Outbreak Context
Photo caption: A white-tailed deer observed along the riverbank of the Looking Glass River, a typical habitat where EHD outbreaks are prone to occur. Courtesy of DNR.
The discovery of a deceased deer in a local yard prompted a resident to contact The Sun Times News, expressing concern over CWD—an illness more widely recognized among the public due to its chronic, neurological progression. Yet DNR investigations highlight that the recent deaths align more closely with EHD, which tends to spike during late summer and early fall seasons.
DNR Confirms EHD Presence in Washtenaw and Surrounding Counties
In 2025, the DNR, in partnership with Michigan State University’s Veterinary Diagnostic Laboratory and the Southeastern Cooperative Wildlife Disease Study, confirmed cases of EHD among free-ranging white-tailed deer across Eaton, Jackson, Van Buren, and Washtenaw counties. These findings mark Michigan’s initial detections of EHD for the year.
EHD is a viral disease transmitted by biting midges (Culicoides spp.), which act as biological vectors. Unlike CWD, which involves prions that spread directly between deer through bodily fluids or contaminated environments, EHD cannot propagate from deer to deer without an insect intermediary.
Expert Perspective on Outbreak Patterns
Brent Rudolph, a deer, elk, and moose management specialist with the DNR Wildlife Division, notes that past EHD outbreaks typically affected only a handful of counties. However, exceptional years—such as 2012—saw disease presence across multiple counties, sometimes exceeding thirty.
The timing of outbreaks often correlates with environmental conditions. Specifically, a wet spring followed by a hot, dry summer fosters ideal conditions for midge populations to thrive, increasing transmission risk. The arrival of frost ultimately curtails midge activity, thereby ending the outbreak period.
“Deer surviving EHD infections develop immunity to the virus, which is why recurrent outbreaks in the same locations during consecutive years are uncommon,” said Rudolph.
Biological Comparison: EHD versus CWD
- Cause: EHD is caused by a virus transmitted by biting midges; CWD is caused by misfolded prion proteins transmitted directly between deer and through environmental contamination.
- Onset and Progression: EHD typically results in rapid mortality within 1–3 days following symptom onset; CWD progresses slowly over months to years.
- Visual Symptoms: Deer with EHD may appear healthy until sudden death, whereas CWD-affected deer show weight loss, drooling, and disorientation.
- Seasonality: EHD outbreaks occur mainly in late summer and early fall; CWD is not seasonally restricted.
- Transmission: EHD does not spread deer-to-deer directly; CWD is contagious among deer.
- Outcome: Some deer survive EHD and gain immunity; CWD is invariably fatal.
- Control: EHD outbreaks subside once frost kills midges; CWD requires ongoing management due to environmental persistence.
Monitoring and Reporting
The DNR advises that dead or sick deer related to EHD tend to be found near water sources where biting midges breed. Reporting such findings helps wildlife professionals monitor disease prevalence and manage population health effectively.
Additional reporting and sources from: Recent Washtenaw Deer Deaths Likely Caused by EHD, Not CWD – The Sun Times News
