Why Drought Isn't the Only Factor in Deer EHD

Why Drought Isn't the Only Factor in Deer EHD

Epizootic hemorrhagic disease (EHD) and its relative, bluetongue, are transmitted to whitetails by tiny midges that hatch from mud in late summer into fall. The viral outbreaks are often associated with drought — but they can occur even when water levels aren't low. In fact, this summer EHD flared up in several states, including Kentucky, Pennsylvania, Tennessee and Ohio, that had been experiencing normal to above-normal rainfall.


From late summer until first frost, a dead whitetail in or near water is reason to suspect a viral outbreak. (Photo courtesy of Jason Suman)

"EHD and bluetongue viruses can be associated with drought, but it's not a requirement," said Gabe Jenkins, deer program leader for Kentucky's Department of Fish & Wildlife Resources, when asked for an update in August. "We know it's one of many potential factors.


"In the recent decade, when the most severe outbreaks occurred in 2007 and 2012, most of the outbreak areas were experiencing a severe drought," the biologist noted. "However, every year across the country there are local EHD outbreaks not associated with a drought. We are above normal precipitation levels in eastern Kentucky.


"The key factor in outbreaks is the creation of large silt/mud deposits the midges need to breed," Jenkins noted. "One school of thought is that, yes, we're above normal precipitation — but the drought index doesn't depict the true story. East Kentucky has been fairly dry with a handful of significant events where multiple inches of rain hit in a very short time. Those rain events could have produced large amounts of silt and created mud deposits a drought would have normally provided."

And there's another factor at work.

"Herd immunity is the biggest factor, and we've not had a major EHD outbreak in East Kentucky since 2007," Jenkins added. "Thus, our herd is pretty susceptible to the disease. The loss could be extremely severe in some areas and non-existent in other areas."

Cold weather kills the midges, halting the cycle. So hunters in areas with late frosts are advised to remain alert. If you find a whitetail that appears to have died from natural causes — particularly in or near a waterway — notify wildlife authorities at once.

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