December 13, 2016
By Dr. Grant Woods
Last month, I shared information about Chronic Wasting Disease and the long-term impact it is having on deer populations across the nation. Although we shouldn't panic about CWD, we should work to limit its spread. Based on current information, the best two actions we can take to contain CWD are to stop all transportation of live deer and elk, and for hunters to only remove the meat, pelt and antlers of deer and elk tagged in areas where CWD is known to occur.
Because infection rates of CWD usually start very low and take years or decades to significantly increase, many hunters tend to ignore CWD. But in the case of another deer malady known as Epizootic Hemorrhagic Disease, the impact on local deer populations can be immediate and devastating — often causing EHD to dominate the headlines and hunters' conversations.
What is EHD?
Commonly known as Bluetongue, EHD is caused by a virus. There are several variations of EHD, and new ones have been identified in recent years. Some of these new variants are more virulent, and some researchers believe these new variants of the EHD virus have arrived in the whitetail's range via exotic pets.
EHD is spread deer to deer by very small biting flies called midges. These midges breed in mud, and there is often more mud and breeding habitat for the midges during a drought. Because water sources are limited during droughts, more deer tend to come to few water holes and the incidence of EHD often increases. This is why EHD outbreaks tend to occur during the late summer and fall, when dry conditions are most likely to occur.
Deer with EHD can exhibit many different symptoms, including lethargy, high fever and trouble breathing. Infected deer are often found near or in
water. This is believed to occur due to having a high fever.
There are acute and chronic forms of EHD. Deer with the acute form often die within a few days. Deer with the chronic form may or may not survive. Deer that do survive the chronic form often show signs of interrupted growth in their hooves, or where they've sloughed their hooves.
Mortality from EHD can vary from low to more than 50 percent! There was a widespread drought throughout much of the Midwest during 2012, and a very widespread outbreak of EHD occurred. Based on trail-camera surveys before and after this outbreak, more than a third of the deer died at my farm in Missouri.
My wife, Tracy, really enjoys shed hunting. I usually enjoy examining the sheds she and her dog, Crystal, find. However, during the months following the 2012 HD outbreak I grew very tired of Tracy bringing in skulls of bucks I'd been watching for years. It was very disheartening to walk into our shop and see a growing pile of skulls from mature bucks, not to mention the number of does she reported finding.
The fall of 2013 was filled with lots of hours in a treestand with fewer than normal deer observations for my farm. We did have a few mature bucks on camera but backed off the doe harvest that year. I was able to tag a nice buck that fall — even after approximately a third of the local herd died due to the EHD outbreak.
Fast-forward to this year, and my friends and I need to tag several does to reduce the deer population at our farm. This is a typical pattern following an EHD outbreak. Even without restricted regulations, hunters tend to back off the doe harvest for a year or two after they find or hear reports of lots of dead deer. Whitetails have the ability to reproduce rapidly and herds have been known to fully repopulate in just a few years after an EHD outbreak.
At my property, my friends and I need to harvest lots of does this fall! Even though we had a good doe harvest last year, there are clearly more deer than quality browse at my place this year. To maintain a healthy herd and habitat, we need to remove twice as many does this season.
EHD has been studied for more than five decades. It can certainly have devastating impacts on local deer herds. However, there's a clear history of herds that have suffered a significant die off from EHD recovering relatively rapidly if hunters reduce the doe harvest for a year or two after the outbreak.
EHD is much different than CWD. Lots of deer infected with EHD survive, but there's never been a deer known to survive CWD. EHD is spread deer to deer by biting flies. These flies die once a hard frost occurs. CWD is caused by prions (abnormal proteins) and infected deer can shed these proteins in their urine, feces, and other bodily fluids. Hence, deer can become infected with CWD anytime throughout the year and the prions remain active in the soil. In fact, researchers haven't found a method to remove prions from the soil.
EHD outbreaks are very cyclic, while CWD infection rates tend to increase as more prions are deposited in the environment. EHD can cause a huge ruckus when folks hear and/or find lots of dead deer during the late summer and fall near water sources. However, we should all be more concerned about CWD, given it appears to be 100 percent fatal and there's no known method to remove the causative agent from the environment.
Both of these diseases can have a huge impact on deer herds. However, deer herds have successfully recovered from EHD for decades. That's not the case with CWD. This fall, let's help and keep an eye out for deer that display the signs of either.