Managing Deer Diseases: EHD and CWD

Is there anything hunters can do to protect the herd from disease?
Managing Deer Diseases: EHD and CWD

By now you've heard about the summer outbreaks of epizootic hemorrhagic disease (EHD). As is usually the case with EHD, some areas got hit harder than others. Michigan estimates that they lost more than 10,000 deer in 29 counties to the disease, but almost all northern whitetail states lost deer. From Montana to Delaware, EHD took deer, but Michigan, South Dakota, Illinois and Nebraska seemed to be affected more than most states, and at least two of those states modified and lowered deer hunting permit numbers in hard-hit areas of their state. As is usually the case, southern states had fewer reports, probably because their deer have been exposed to EHD for many years and many have built up an immunity to the disease.

The culprit for EHD is a tiny insect, a midge, and the summer of 2012 provided a perfect storm for that insect. Drought conditions create mud flats along shrinking streams and lakes, and it is postulated that these muddy areas are perfect for midge reproduction. This situation is made even better for the midge when a rare rain does come, because these muddy areas will lead to the production of even more midges.

A week or two after the infected midge bites a deer, that animal gets very sick very quickly. The disease literally eats away the lining of the digestive tract from the mouth to the intestines. This causes hemorrhaging (hence the name), with lots of blood loss and high body temperatures. It is the high fever that leads sick deer to water, where most will die in a day or two. The threat of disease ends with the first fall frost that zaps the insects that spread EHD.

We probably lose some deer to EHD every year, but losses are small and might not even be noticed. But when we get the perfect-storm situation, as we did this past summer, mortality jumps and hunters become concerned.

Is there anything that agencies or hunters can do to alleviate the problem? Are there any management practices that will lower mortality from EHD? In a word, the answer is no. One would think that in areas with lower deer numbers, the prevalence of EHD would be lower, but the reality is that you would have to manage your herd to such low numbers that hunting would be affected. No, hammering the herd via hunting would not work relative to EHD.

Will EHD then wipe out all deer in an area in those really bad years? No, because some deer survive and develop antibodies, making them immune in the future. In fact, you can sometimes identify EHD-immune deer from their hooves. The high fever causes an interruption in the growth of the hoof, leading to split hoofs and a peeling away of the walls of the hoof. This can be observed when that deer is shot during the gun season. This means that deer in that area were lost to EHD, but some also developed immunity.

In rare instances, one particular area, usually along rivers, will lose high numbers of deer to EHD. In those cases it may take three or four years for that herd to recover, but in most areas the impact is minimal and overall deer numbers will be right on target within a year. Statewide, even when high numbers of deer die, the overall impact is minimal. For example, even though Michigan saw the loss of more than 10,000 deer spread over 29 counties, with an estimated deer herd of 1.7 million, the impact of EHD at the state level was hardly a blip on the screen.

Slowing CWD

Though there isn't much one can do about EHD, there are things to be done to slow the spread of chronic wasting disease (CWD). CWD erupted on the scene in 2002 when it was found on a deer farm. Today CWD is found in 20 states and two provinces with more to come in the future. Sometimes the first deer found with CWD in a state is a deer in the wild. For example, in July 2012, two mule deer in the wild in West Texas were found to be CWD-positive. Most likely that CWD came from deer in New Mexico that spread from deer to deer to reach Texas.

More often the first occurrence of CWD in a state is on a game farm or shooting preserve (hereafter listed as deer farms for simplicity). Three recent cases illustrate that point. In February 2010, CWD was found on a deer farm in Missouri. In 2011 CWD was found at a second deer farm. Then in 2012 two wild deer were found with CWD from hunter harvests within two miles of one of those deer farms. More than 650 deer were then sampled (i.e., harvested) in a 160-square-mile area around these deer farms, and three more positive deer were found within two miles of the deer farm. Clearly deer farms were the source of the CWD in the wild in Missouri.

In July 2012, CWD was first found in Iowa, and it was on a deer farm. And in October of 2012, CWD was found on a deer farm in Pennsylvania. Interestingly, when agriculture department officials went to that farm to depopulate 10 remaining deer, one escaped to the wild. As I write this in November 2012, it is not known if any of those 10 deer, including the escapee, had CWD.

We know that CWD can be spread from one deer to another by direct contact. Thus, increasing hunting pressure around contaminated deer farms will slow the spread. With luck and an early detection both on and around the deer farm, it is possible to eliminate the disease. New York is one good example of this — where CWD was found in 2005, heavy hunting was done in that area, and no further deer have been found with CWD. However, in most situations CWD slowly spreads from the initial positive area. Though you cannot usually shoot your way out of CWD, increasing hunting pressure slows its spread.

One theoretical mode of transportation of CWD to new areas is via live and dead deer. Thus, when a deer farm tests positive, movements of deer in and out of such farms are eliminated. In addition, many states set up a zone around the positive finding and set regulations concerning movements of whole hunter-harvested carcasses. At the same time, other states set regulations about the import of hunter-harvested carcasses from CWD areas. For example, in 2012 New York implemented a rule preventing the import of certain deer body parts from Pennsylvania. New York hunters cannot bring in deer brain, spinal tissue, tonsils, intestines, eyes, spleen and certain lymph nodes. In other words, an imported deer killed in Pennsylvania would most likely be butchered before taking it home. North Carolina just enacted a regulation preventing any of their taxidermists from doing a deer killed in Pennsylvania. There probably aren't many bucks harvested in Pennsylvania that would be mounted by a North Carolina taxidermist, but that now would be against the law. All such rules are implemented to prevent or slow the spread of CWD. You can find a state-by-state listing of such rules at

There are precautions that hunters can take relative to CWD. Even though there has never been a case where CWD was passed on to humans, such cautions are worthwhile for hunters to consider. Wear latex gloves when handling your deer. Bone out the meat and do not cut through bone, especially avoiding the spinal cord. Avoid handling or consuming the brain or spinal tissue. Remove as much fat as possible, especially the lymph nodes.

You can restrict carcass transportation from CWD areas, but the big sticking point for slowing the expanding range of CWD is that it is spread by indestructible prions that apparently can remain viable in the soil for years. In fact, we really do not know how long they remain viable. We do know that prions have a better chance of being spread where deer congregate in large numbers, such as is found on deer farms or bait sites.

Baiting is a sacred cow for hunters. In states where it is illegal to bait, hunters continue to ask for it. In most states where it is legal to bait, the state wildlife agency would like to see it go away, mainly because of the spread of disease. And in states where it is legal to bait and where there is CWD, baiting rules are commonly modified. For example, in West Virginia, where baiting is legal, the state wildlife agency made it illegal in the counties in the eastern panhandle where CWD is found. In Michigan there are different baiting rules for different parts of the state. In areas with the potential to spread CWD, you can only put out bait from October 1 to January 1. You can only place two gallons of bait at one site and it must be spread over a 10-foot square area.

CWD is a different animal than EHD in that you can do certain things to slow its spread. Relative to CWD and you the hunter, when CWD hits your state, become aware of the rules laid out by the state wildlife agency and follow them. In doing so, you will be just fine and able to enjoy another deer hunting season.


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