Deer, Chronic Wasting Disease, And You

Oct 8, 2017

Hunting is an activity that crosses state lines, with hunters looking for the best spots for game, and game not even having a concept of political boundaries. But a disease is infecting deer herds in both Illinois and Wisconsin, and it could pose a threat to hunters. 

Chronic Wasting Disease is a malady that’s existed among deer in the region for more than a decade. It was first detected in southern Wisconsin around 2002. Since then, infected herds have spread to at least 19 counties.

Tami Ryan is Chief of the Wildlife Health Program for the Wisconsin Department of Natural Resources. She said the way they track the spread puts the number closer to 43 counties.

“If CWD is found in a county, a ten-mile radius is drawn around that finding and, if that circle should hit a portion of the county, the entire county then gets identified as being CWD Affected," she said.

Illinois detected the disease around the same time as Wisconsin, with their first sample near Roscoe. Doug Dufford, a Wildlife Disease Program Manager at the Illinois Department of Natural Resources, said the initial spread was limited to a band along the Boone/Winnebago county line. It extended along the south fork of the Kishwaukee River into northwest DeKalb County. DNR now focuses on managing infected populations.

“Densities will be lower in those infected areas," he said. "There will be less transmission between individuals as well as fewer sick animals that will move away or emigrate or move out of infected areas and potentially infect new areas.”

Credit IDNR

This strategy has kept these areas at around a 1-percent infection rate, but hasn’t been very successful at preventing geographic spread. Chronic Wasting Disease is now in more than 17 Illinois counties, including as far south as Livingston County, west into Jo Daviess County, and eastward to Kane and Lake Counties.

Normally, the biggest concern from this kind of disease would be how it kills off the deer population. But a recent study suggests the possibility of deer-to-primate transmission. The University of Calgary in Alberta, Canada, introduced the disease to some of our genetic relatives. They fed Macaque monkeys CWD-infected venison, and three out of five tested positive for the disease.

However, Dufford said that doesn’t mean definitive proof of transmission between deer and human.

“To date, there’s not been a case that a human has developed a prion disease associated with the consumption of infected venison," he said. "Now, that’s not to say it’s not possible, but it’s not been confirmed.”

Regardless of these findings, Dufford said what makes Chronic Wasting Disease particularly difficult to address is what causes it. CWD doesn’t rely on bacteria or viruses to spread. Instead, it comes from structures called prions.

“They’re actually misshapen proteins that become incorporated into the nervous tissue in the lymphatic system of the animal and essentially cause those systems over time to stop functioning properly,” he explained.

Prions also are responsible for conditions like Mad Cow and Creutzfeldt-Jakob disease, both of which cause fatal brain degeneration. Chronic Wasting Disease travels between deer mainly through saliva.

“Through nuzzling of does to fawns or just communicating between individuals through scent stations and licking posts,” Dufford said.

Once a deer is infected, it can take up to two-and-a-half years before the animal finally perishes. During that time, bodily functions begin to diminish. Near the end of its life, Dufford explained, an infected deer can appear to be literally wasting away.

Credit Wisconsin DNR/CWD Alliance

“Losing weight, it would be very thin," he said. "The hip bones and rib bones would start to stick out. Oftentimes, they’re unresponsive, so they’ll have a blank stare about them. They won’t flee from humans.”

But that isn’t the end for the prions. They don’t decay in the environment -- especially if spread by feces, urine, or corpses. These misfolded proteins can remain in soil for as long as five years, and plants also could absorb them through the roots, infecting any deer that eat the plants.

Dufford said ground accumulation is only a problem in areas with many infected deer. But the issue of infected venison remains. The Centers for Disease Control and World Health Organization both advise against consuming the meat, and Dufford noted that standard food preparation won’t get rid of the malformed proteins.

“These prions can remain infectious after being raised to temperatures in excess of 2000 degrees, so cooking the meat has never been identified as a method to deactivate these proteins.”

Registering a CWD infected deer for sampling.
Credit Wisconsin DNR

Thus, both Illinois and Wisconsin recommend that hunters have their harvest tested for the disease. The Illinois DNR has offices that test for the disease, as well as state-partnered vendors that also carry out the procedure. Ryan says Wisconsin’s system is more sophisticated. Hunters register each deer tag electronically and can get a better idea of whether their deer is at risk.

"They receive a message basically letting them know if they’ve harvested an animal from a CWD-affected county or even just an area of the state where we’re interested in collecting samples," she said.

These samples are then used to shape the state’s annual management plans. As for testing options, Wisconsin has both DNR stations and vendors that can perform the tests, such as gas stations and bait shops. Ryan said they also have self-service kiosks.

“You drop off a head in a cabinet or a freezer. There’s supplies on hand, datasheets on hand. Provide us with information we need to collect that sample, and then the staff in our system will take it from there.”

In the most remote areas, Wisconsin has partnered with veterinarians but, unlike other options, hunters have to pay out of pocket (the other testing sites are supported by DNR funds, such as the sale of hunting licenses).

Finally, Illinois and Wisconsin have structures to their hunting season. Illinois has a standard deer season for bows, firearms, and muzzleloaders, but also offers a late-winter season where hunters can go after deer in counties affected by Chronic Wasting Disease.

Wisconsin had a similar system during the early years of the disease, but Ryan said it lost public support.

“So essentially it’s more of a response to surveillance, getting the information collected that can help inform where the disease exists so that hunters know whether or not CWD is in the areas in which they’re hunting," she said.

Now, Wisconsin has a standard season like Illinois. 

Ryan and Dufford say hunters have several ways they can prevent Chronic Wasting Disease from spreading further. First and foremost, both states urge hunters to report any sick deer they may encounter to local wildlife personnel. That information, they say, is invaluable to disease management plans.

That goes double for testing herds and ensuring that carcasses are disposed of in a manner that doesn’t contaminate the environment with more prions. Finally, despite no confirmed cases of deer-to-human transmission, tainted venison should not be consumed under any circumstances.