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Wisconsin Whitetails Under Siege: Chronic Wasting Disease Update

Wisconsin Whitetails Under Siege: Chronic Wasting Disease Update
CWD is a serious issue in Wisconsin, and just because a deer looks healthy doesn't mean it is. (Photo by Ron Sinfelt)

CWD is a serious issue in Wisconsin, and just because a deer looks healthy doesn't mean it is. (Photo by Ron Sinfelt)

In the decade and a half since Chronic Wasting Disease showed up in our state it has continued to spread. So how does that impact the coming hunting season?

Wisconsin, we have a problem.

Since Chronic Wasting Disease (CWD) first reared its ugly head in Dane and Iowa counties in 2002, the disease has spread to other areas of the state. Efforts to control CWD were met with serious resistance, and subsequently curtailed, and each year the disease is detected in additional deer.

Both wild and captive deer have been infected, and the prevalence of CWD in deer in north-central Iowa County has increased to the point where now nearly half of adult bucks sampled test positive for the disease.

Just how serious is this situation and what, if anything, can be done about it? How does the presence of CWD affect hunters and their families? And what the heck is CWD in the first place?

We posed these questions and more to several experts in the field and offer their take on CWD and their advice to hunters as they prepare for the 2018 Wisconsin deer seasons.


Chronic wasting disease is a transmissible spongiform encephalopathy (TSE) that affects white-tailed deer, mule deer, elk, moose and caribou or reindeer. The disease was first identified in 1967 in captive mule deer at a wildlife research facility in Colorado. Since that time, CWD has spread to wild and captive populations in 25 states, two Canadian provinces, South Korea, Norway and Finland.

Related: CWD Spreads to New State

Like other TSEs, CWD affects the central nervous system of infected animals. The disease is progressive and always fatal once it enters the central nervous system. Most cases occur in adult animals, and deer that contract CWD may appear perfectly normal for a year or more after they have been infected. During this time, however, the disease progresses and the central nervous system continues to deteriorate.

During the brief clinical period, infected deer may show signs of weight loss and exhibit behavioral changes, such as decreased interaction with other animals, listlessness, lowering of the head, tremors and excessive salivation. Infected animals often show signs of increased drinking and urination.

early season bow huntingThe sickness is caused by an abnormal form protein produced by all mammals, called a prion. Prions are most commonly found in the central nervous system, but can spread to other tissue, including muscle.


"Chronic Wasting Disease is transmitted via the uptake of the infectious form of the prion protein," says Bryan Richards, CWD coordinator for the US Geological Survey's National Wildlife Health Center in Madison. "CWD-positive animals shed that infectious agent through their bodily fluids, including saliva, feces and urine. So, through close physical contact, including nose-to-nose contact, it's fairly easy to see how that infectious agent can be picked up by a healthy animal."

The disease may also be transmitted from an infected female to her offspring before birth. Carcasses or even parts of carcasses from infected deer left on the land by hunters or when deer die of CWD or other causes can also contaminate soil and thus serve as a disease vector.

There is no evidence that CWD has been transmitted to humans. However, the Centers for Disease Control (CDC) recommends that hunters avoid eating the brain, spinal cord, eyes, spleen, tonsils and lymph nodes of deer taken from areas where CWD has been found. The CDC also recommends that hunters, in areas with CWD, strongly consider getting their deer tested, and if one comes back positive, not consume it.

"A recent scientific study by Canadian researchers involving CWD was conducted using macaques, a close primate relative of humans," Richards says. "Some of the animals in this study were fed CWD-positive venison, the same thing you or I might consume if we don't get our deer tested, and several of these animals did contract CWD. To date, there are no known instances where CWD has caused the disease in humans; however, the bulk of the science conducted suggests there is a small positive chance the disease could cross over into a human host. It does not, however, indicate that CWD will become a human disease."


Wisconsin Department of Natural Resources biologists began monitoring deer for CWD in 1999. The first positives were detected in 2002 in deer killed by hunters during the 2001 season in western Dane County. The state's initial response was to attempt to drastically reduce deer numbers in the affected area in order to disrupt disease transmission, using long seasons, liberal antlerless harvest, earn-a-buck and government sharpshooters.

This went on through 2006, but the approach did not go over well with some landowners and hunters, which led to political and social pressure that forced the DNR to abandon active disease management.

The state then developed a 15-year CWD Response Plan to guide the diease management from 2010 to 2025. The plan calls for minimizing the spread of the disease, but in reality, the state is merely monitoring its progress where it has become established and attempting to determine whether new cases are isolated incidents or new outbreaks. The full plan can be viewed or downloaded from the DNR website, keywords "CWD Response Plan."

Meanwhile, CWD continues to spread. The disease has been detected in 24 counties in wild deer, 10 counties in both wild and captive deer, and 7 counties in captive deer only.

Since CWD testing began, and as of this past spring, the state has tested 211,109 deer for CWD and found 4,182 positives. In 2017-18, the state tested 9,881 deer, of which a record 599 tested positive. The totals for 2016-17 were 6,158 tested and 448 positives.

Only small numbers of hunters have their deer tested, however, so there is little doubt some hunters are shooting and consuming CWD-positive deer without knowing it. In Iowa County, where 2,260 deer have tested positive, only about 15 percent of deer taken there in 2017 were tested.

As a case in point, in Lincoln County only 32 deer taken by hunters during the 2017-18 season were tested, but one, a 2-year-old buck, was found to be infected. The hunter who shot it said the deer showed no sign of being sick. This was the first recorded incidence of CWD in a wild deer in the Northwoods since an adult doe from Washburn County was found to be positive in 2011 and only the second CWD-positive wild deer in that area since testing began.

The state has several levels of response to CWD, none of which could be expected to alter the course of the disease on the ground. When a new positive is found, an immediate feeding and baiting ban is put in effect in that county and any counties within 10 miles of the infected deer.

In the case of the Lincoln County deer, an additional 75 deer from a 10-mile radius were tested in winter and spring, including car-killed deer and deer taken with nuisance, scientific collection and agricultural damage permits. Surveillance permits were also issued to landowners, who were asked to help collect the 75 deer needed for testing. As of this writing, one of those deer –– an Oneida County doe –– had tested positive for CWD. This was the first positive in a wild deer in Oneida County.

A baiting/feeding ban is now in effect in 42 of Wisconsin's 72 counties.

Under current regulations, when a new CWD-positive deer is found, baiting and feeding are banned for three years in the county where the deer was killed and for 2 years in counties within 10 miles of where the deer was killed. If no new CWD-positive deer are found in a county, these bans are lifted after the periods end.

The state will test any deer for CWD at a hunter's request. Head-collection and testing facilities are located in areas of southern Wisconsin where the disease is most prevalent and in areas where new positives are found. Elsewhere in the state, a number of taxidermists and deer processors will collect tissue samples at no charge to the hunter and forward them to the DNR.

A list of sampling stations and cooperating taxidermists and processors can be found on the DNR website, keywords "CWD Sampling." To help pay for CWD sampling, the state uses $5 from each bonus antlerless harvest authorization tag sold in CWD-affected counties.


The deer-hunting regulations booklet and the CWD pages of the DNR website offer advice for hunters regarding CWD. The rules for transporting carcasses and deer parts are too complicated to explain here, so check the regulations for details. In general, though, if you move a carcass, you should assure that all inedible parts are land-filled instead of ending up on the back 40, where they could transmit disease.

Hunters should also follow the law on baiting and feeding of deer. Even where legal, Richards suggests hunters refrain from using bait.

"If you're doing anything, including baiting or feeding, that brings inordinately large numbers of deer into the same space and time; if one of those animals is infected with CWD and is actively shedding that agent out into the environment, that enhances greatly the risk of transmission at those sites," Richards says.

Hunters should wear rubber or latex gloves when field-dressing deer, bone out the meat using knives designated only for that purpose and minimize handling of the brain, spinal cord, spleen and lymph nodes. It is also advisable to thoroughly clean all knives and equipment, soak all butchering implements in a 50/50 solution of chlorine bleach and water for an hour, wipe down all countertops and work areas with the same solution and pressure wash any vehicles or equipment moved to and from areas of known CWD contamination.

The DNR also advises hunters label and freeze meat from deer that are being tested and keep it separate from other venison until test results are known. It may take several weeks to get test results, depending on the volume of tests in the pipeline.


It is widely believed that deer farms are a major contributor to the spread of CWD. On several Wisconsin deer farms, a number of deer have tested positive for the disease. Early in the state's experience with CWD, deer farms with infected deer were depopulated, but that is no longer the case. There are currently five shooter facilities with multiple positives that are still in business in counties where CWD has not been detected in wild deer.

There's a lot of debate over management of deer and elk farms, which was formerly regulated by the DNR. After CWD was detected here, the captive cervid industry successfully lobbied for transfer of that regulatory authority to the Wisconsin Department of Agriculture, Trade and Consumer Protection. The only authority over deer farms remaining with the DNR is to oversee fencing.

To date, the captive industry has successfully fought efforts to force deer farms to install double fences to prevent nose-to-nose contact between captive and wild deer. David Clausen, a retired veterinarian and former chair of the Natural Resources Board, is now one of the most outspoken proponents of double fencing.

"Better regulation of the captive industry will not cure CWD," Clausen wrote in a published opinion piece. "But it is an important step in preventing the spread of CWD."

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Clausen also would like to see immediate depopulation, with indemnification, of all CWD-positive deer farms, and a ban on movement of deer out of all CWD-positive facilities and all facilities in CWD-endemic counties.

A five-year research project, the largest and most comprehensive of its kind ever undertaken in the state, is looking at the impact of predators, like coyotes and bobcats, habitat suitability and hunter harvest on deer survival, as well as population growth in CWD-endemic southwest Wisconsin. The study is just beginning its second year, but early results have shown that the annual survival rate for CWD-positive deer was about 25 percent, whereas for deer without CWD it was about 75 percent. Clearly, CWD kills deer or predisposes them to other sources of mortality.

In the face of the CWD crisis, what should hunters do? Don't give up hunting, Richards says, but if you hunt where CWD exists, consider having your deer tested and make sure the carcass does not end up out on the landscape because you will not likely have test results back before you need to dispose of carcass waste.

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