Epizootic Hemorrhagic Disease Transmitted by Infected Midges Kills Deer: Southeastern Ohio is a Hotspot in 2025: Climate Change is Certainly an Important Factor

     Every summer, I get bitten by some biting midges, usually more in the late summer and fall. The midges are too small to see. Thus, they are often called "no-see-ums." Some call them chiggers. The bites itch for a day or two. I went through some clouds of them down in the woods, apparently, a few weeks ago, and had bits all over me that itched for nearly a week. They really itch but are otherwise not a problem for humans. However, for deer, they transmit at least two diseases. One is the very deadly Epizootic Hemorrhagic Disease, or EHD, that causes fever and death within a few days. When the deer get feverish, they seek out water sources to cool down. While it rained a lot in midsummer, which increases midge populations, we have been in a mild to mid-level drought for several weeks. The midges seem to do well when there is drought in late summer and fall, which is fairly common here. I have seen at least two dead deer in ravines, and the smell of death has pervaded areas where I hike here in southeastern Ohio. In fact, the smell of death from rotting carcasses has been much more common on my hikes this summer. Other local people I have talked with have also seen several dead deer this year. One person I know had so many midge bites on her legs that weren’t going away that she went to urgent care.

     In 2024, it was predicted via modeling what would make an ideal likelihood for the disease to spread. Dr. Sonja Christensen of the Christensen Lab for Wildlife Population Health at Michigan State University described the model for a fast spreading of midge populations and disease transmission to the deer in an article for the National Deer Association.

“The best model was above-average spring temperatures plus increased July precipitation plus decreased August precipitation,” said Sonja. “These are stand-alone variables in the model, and when they were all together, that is what created the higher likelihood of disease outbreak. One alone might contribute, but it really wasn’t meaningful in the dataset unless you had all three players happening in a county at the same time.”

     That model was confirmed, unfortunately for the deer, in 2025 in Southeastern Ohio, where all three variables made it ideal for midges. Lindsay Thomas Jr. of the National Deer Association wrote in that 2024 article:

“This combination makes sense given the reproductive ecology of Culicoides midges. Above-average spring temperatures mean insects can become active sooner and begin building populations early. High July precipitation fills lakes, swells creeks, and pushes rivers into floodplains. But if rain shuts off in August, those waters recede leaving abundant mudholes and silty breeding grounds for midges during the hottest part of summer when virus replication peaks inside the insects.”

“The result is a collision between clouds of virus-filled midges and hot, thirsty whitetails seeking a drink at shrinking pools of stagnant water.”

     Culicoides midges generally emerge from mud holes in low areas, some that have been inundated and later left mud holes with water. However, this year, it has been noted that more are being found on uplands and ridges. I can confirm that since I have seen one dead in an upland ravine just below the ridge I live on. Some deer will recover from the disease but many die within three days of the onset of symptoms.

     An article by the Maryland Department of Natural Resources notes:

“EHD occurs annually but its distribution and occurrence are highly variable. Occurrence may involve a few scattered cases or may appear as dramatic, highly visible, localized outbreaks. The onset of freezing weather typically kills the midges that transmit the virus and brings an end to EHD outbreaks.”

     The Ohio Department of Natural Resources (ODNR) gives the following description of deer symptoms and recommendations regarding EHD:

     I saw one doe stumbling and looking very distressed in the facial area, coming from a creek across the road in front of me. I am guessing she was affected.

     ODNR also has an interactive map where they document cases and suspected cases of the disease, as shown below. I reported the two dead does I saw on my property, both in upland ravine areas, after the latest map update.  

 

The Connection to Climate Change is Pretty Clear

     The disease is moving north, where deer populations have not developed immunity, as they have in the south, where the midges are more common. The other disease transmitted to deer by the midges is Blue Tongue Virus (BTV). It is also moving north as more midges emerge northward as well. Christensen surmises that warmer springs, likely due to climate change, have made one of the three variables much more common in recent years, aiding the spread of both diseases. The disease does not transfer from deer to deer, so the environment, the weather, and subsequent deer behavior are important factors for disease spread.

“Milder winters and warmer summers are inviting the Culicoides midge to spread northward into states where they couldn’t previously survive.”

EHD and BTV are strongly emerging in states like West Virginia, Ohio (especially Southeastern Ohio), Pennsylvania, Virginia, and Maryland, and began to appear around 2012 in states further north like Michigan and Wisconsin, especially in ideal years. Deer populations usually recover from these diseases, especially as weather makes ideal conditions unlikely in some years, but some states are considering changing hunting limits in certain counties due to the losses.

     The diseases are clearly moving north, and this is almost certainly due to the warmer spring temperatures and perhaps to milder winter temperatures in general. While years will vary due to the other variables: weather and deer behavior, the average regional temperature rise is fairly consistent. I do not usually condone attributing events strictly to climate change, and that is true here as well, since there are other factors. However, climate change is clearly a very important key factor in this case, making outbreaks of the disease more likely in emerging areas. The disease could be depicted as climate-change driven, although other factors should also be acknowledged. The good news is probably that deer in these areas will eventually develop immunity as they did in the south.

 

 

    

References:

 

Wildlife officials confirm deer disease in five West Virginia counties. Cassidy Roark. The Dominion Post. September 9, 2025. Wildlife officials confirm deer disease in five West Virginia counties - Dominion Post

Epizootic Hemorrhagic Disease (EHD) in Ohio. Interactive Map. Ohio Department of Natural Resources. Last Updated: September 11, 2025. EHD Experience

EHD deer disease outbreak found in Ohio. Here's what to know. Kevin Sutton. Cambridge Daily Jeffersonian. August 30, 2025. EHD deer disease in Ohio: Outbreak could affect hunting

Maryland Experiencing Hemorrhagic Disease Outbreak in White-tailed Deer. Maryland Depart of Natural Resources. September 10, 2025. Maryland Experiencing Hemorrhagic Disease Outbreak in White-tailed Deer

These Warning Signs Could Predict EHD Outbreaks in Deer. Lindsay Thomas Jr. National Deer Association. July 16, 2024. These Warning Signs Could Predict EHD Outbreaks in Deer