Epizootic hemorrhagic disease (EHD) is transmitted by biting midges, not spread deer-to-deer, so prevention comes down to reducing midge populations and limiting contact between midges and deer. There is no commercially available EHD vaccine for deer, and once an outbreak begins, there is no treatment. That makes habitat management and insect control your primary tools.
How EHD Spreads
EHD is caused by a virus carried by tiny biting flies called Culicoides midges, sometimes known as no-see-ums. In the United States, the confirmed vector is Culicoides sonorensis. These midges breed in warm, shallow, muddy water and are most abundant from August through October. A midge picks up the virus by feeding on an infected deer, then passes it to the next deer it bites. After a bite from an infected midge, symptoms typically appear within 5 to 10 days, with 7 days being the most common timeline.
The acute form of EHD carries a high mortality rate, especially in northern states where deer populations have had little previous exposure and lack immunity. Deer that survive a mild infection do develop antibodies, which is why southern herds, exposed more frequently, tend to have lower die-off rates during outbreaks.
Why Drought Years Are Worse
Hot, dry summers concentrate deer around shrinking water sources, which also happen to be prime midge breeding habitat. A 15-year study across 23 eastern states found that drought severity was a significant predictor of EHD outbreaks, and the relationship grew stronger at more northerly latitudes, where deer are least likely to carry prior immunity. When water levels drop, ponds shrink into the exact conditions midges love: warm, shallow, muddy, and sunlit. More midges plus more deer crowded around fewer water sources equals a perfect storm for transmission.
Redesign Water Sources on Your Property
The single most impactful thing a landowner can do is make ponds and water holes inhospitable to midge reproduction. Midges breed in shallow, murky, warm water with silty or muddy banks exposed to direct sunlight. They reproduce poorly in clean, clear, deep water with steep, vegetated, or rocky shorelines.
If you’ve built a deer watering hole that fits the description of ideal midge habitat, you can retrofit it:
- Steepen the banks. Gradual, muddy shorelines are breeding grounds. Steep margins reduce the shallow-water zone midges need.
- Establish bank vegetation. Grasses and other plants stabilize the soil, filter sediment, and shade the water’s edge. A vegetated bank is far less attractive to midges than bare mud.
- Locate water sources in shade. Cooler water temperatures slow midge development. If you’re building new water features, place them under tree canopy.
- Keep water deep and clean. Shallow mud holes are the worst option. Design ponds that hold depth even during dry spells.
- Fence out cattle and hogs. Livestock and feral hogs churn up banks, creating fresh midge habitat. If you own cattle, provide an alternative water source during summer and fence them out of small farm ponds.
One often-overlooked detail: if you set out salt or mineral licks for deer, place them well away from standing water. Minerals that leach into nearby ponds can alter water chemistry and contribute to the nutrient-rich conditions midges prefer.
Insect Control Around Deer
Chemical control of Culicoides midges is difficult on a landscape scale, but targeted strategies can reduce biting pressure in specific areas. Ultra-low-volume sprays using permethrin-based insecticides are the standard approach for midge suppression. For property owners managing captive or semi-captive deer, two newer methods show real promise.
A study on a Florida deer farm tested permethrin-treated barriers (fabric panels sprayed with a 0.5% permethrin solution) and permethrin pour-on applications (applied along the deer’s backline). The treated barriers reduced landings of key Culicoides species by 175-fold compared to untreated controls. Pour-on applications reduced landings by 7-fold. The barriers also cut mosquito landings significantly. These results suggest that even simple barrier setups around feeding stations or bedding areas can dramatically reduce midge contact in managed settings.
For wild deer on open land, direct chemical application isn’t realistic. Your best tools remain habitat modification and timing. Midges are most active at dawn and dusk during the hottest months, so any intervention that reduces standing shallow water before and during August through October has the greatest impact.
Is There an EHD Vaccine?
As of 2025, there is no EHD vaccine approved for use in deer. The European Medicines Agency recently recommended approval of Hepizovac, the first EHD vaccine, but it is authorized only for cattle and targets a single virus serotype (EHDV-8). It requires two doses given 21 days apart. While this is a step forward, it does not currently help deer managers in the United States, where multiple EHD serotypes circulate and no deer-specific vaccine exists.
Supporting Herd Health
A deer with a strong immune system is more likely to survive a mild EHD infection than a nutritionally stressed one. Providing year-round mineral supplementation with chelated copper, zinc, selenium, and manganese supports immune function and overall body condition. These minerals are “chelated,” meaning they’re bound to proteins that improve absorption. Vitamins and probiotics in quality mineral supplements further support gut health and immune response.
This is not a guarantee against EHD. A well-nourished deer hit with a heavy viral load from multiple midge bites can still die. But maintaining good nutrition across your herd raises the odds that deer exposed to lower doses of the virus can fight it off or survive with milder symptoms, building immunity for future seasons.
Report Dead Deer During Outbreak Season
State wildlife agencies track EHD outbreaks to map the virus’s spread and predict future risk. If you find sick or dead deer near water from August through October, report it. Most state departments of natural resources have online reporting forms where you can log the county, number of dead deer, their proximity to water, and the specific location. Photos help biologists confirm EHD versus other causes of death.
Reporting does not prevent the current outbreak on your property, but it builds the data that agencies use to issue warnings and allocate resources. In states like Illinois, where EHD flares regularly during hot summers, these reports also influence hunting season harvest recommendations, which helps the broader herd recover after a bad year.