Chronic wasting disease remains a leading threat to deer populations, but according to many experts, it might also threaten Minnesota’s deer hunting traditions.
Marc Schwabendlander is the CWD manager at the Minnesota Center for Prion Research and Outreach at the University of Minnesota. He describes himself as a lifelong hunter and an active member of several conservation groups.
“To put chronic wasting disease in the proper context, we need to think about the deer hunting heritage in Minnesota and across North America,” Schwabendlander said. “Conservation has always been a cornerstone of that heritage, and disease management is a crucial part of conservation.”
Preventing CWD spread
“Preventing the spread of CWD is our top priority,” said Michelle Carstensen, wildlife health program supervisor for the Minnesota Department of Natural Resources. “Once the disease is established in a wild population it’s difficult or impossible to remove.”
Carstensen and her staff are responsible for all disease management in the state’s wildlife populations and coordinate the DNR’s CWD surveillance efforts.
“One of the biggest risks in the spread of CWD is the movement of live animals,” Carstensen said. “Captive deer are one part of that equation, but management agencies also play a part. The Wisconsin DNR, for example, recently completed a multi-year project to re-establish wild elk transported from Kentucky.”
Hunters moving deer carcasses into or even within the state provide another opportunity for the disease to spread. The prions that cause CWD are concentrated in the lymph nodes, spinal cord and brain tissue. A contaminated carcass sheds prions to soil and vegetation and has the potential to infect other deer for years, maybe even decades.
“Minnesota banned the movement of deer carcasses from known CWD zones in 2002,” Carstensen said. “The ban was expanded in 2016 to include any deer or other cervid harvested outside of the state. It’s important for hunters to fully understand and follow the rules.”
Those rules allow the movement of deer parts, including quarters, boned and wrapped meat, antlers and taxidermy mounts into the state. It does not allow for any brain or spinal tissue, even if the animal tested negative for CWD.
The same rules apply to deer harvested in CWD management and control zones until the hunter receives confirmation that CWD was not detected.
“Our goal is to reduce the number of contaminated carcasses on the landscape,” Carstensen said. “The DNR website features videos demonstrating how to quarter and cape a deer, and the Adopt-a-Dumpster program provides an easy way for hunters to properly dispose of their deer carcasses.”
Last year the Adopt-a-Dumpster program collected more than 200 tons of deer remains.
Expanded CWD testing
During the 2019 deer hunting season, hunters in the CWD management zones in southeastern Minnesota were required to submit samples from all deer older than one year throughout the season.
The CWD control zones create a buffer around the management zones where the disease has been found. Hunters in these areas were required to submit samples during the first weekend of both firearms seasons but could voluntarily submit throughout the season.
In the central surveillance area, where CWD has been found in wild and captive deer, hunters were required to submit samples only during the first weekend of the firearms season. Many hunters, though, chose to submit samples throughout the season, giving researchers a much larger sample size.
“The sampling stations were staffed by DNR personnel for 10 hours per day throughout the firearms season,” Carstensen said. “During the archery and muzzleloader seasons, hunters were asked to collect and submit samples on their own.”
Lymph nodes collected from the stations were shipped to the University of Colorado for testing. Results typically were available in three to four business days, except during the firearms season when the volume of samples created a brief delay. Any positive test was retested with a different method to confirm the presence of the disease.
“We’re trying to make this process as easy as possible for hunters,” Carstensen said. “They should register their deer as usual, submit their tissue sample and not move the carcass out of the zone until they receive the test results.”
Carstensen also recommends hunters keep the meat from each animal separated. Many families pool venison trimmings to make sausage and jerky, and one infected animal could contaminate many pounds of venison.
2019 testing results
In 2019, the DNR collected just over 18,000 samples from southeastern Minnesota. Testing revealed 27 positives. Results from seven more samples are still pending.
In the newly formed north-central surveillance area, the DNR collected and tested almost 13,000 samples. No new positives were identified, leading Carstensen to conclude that the disease has not been established in the area.
“We’re also working with taxidermists to collect additional samples,” Carstensen said. “We pay them a $15 fee for collecting a lymph node, muscle sample and a tooth. In 2019, 26 participating taxidermists submitted 1,300 samples that produced seven positive tests.”
Research continues into fast and inexpensive field tests, vaccines and other detection and control measures. But for now, controlling the movement of live deer and high-risk deer parts provides the best defense against the spread of CWD.
CWD panel discussion
A panel of CWD experts gathered at Central Lakes College in Brainerd, Minn., this week to discuss how they’re controlling the spread of the disease. They also answered a range of questions from hunters and others concerned about the lasting impact of CWD.
Marc Schwabenlander is the CWD Research Program and Outreach Manager at the Minnesota Center for Prion Research and Outreach. He is a wildlife disease specialist with a background in wildlife management and veterinary post-mortem investigation.
“Salacious headlines across the country have described CWD as ‘the zombie deer disease,’” Schwabenlander said. “It’s not. And unlike many other diseases, it’s not caused by a virus or bacteria. It’s caused by a misfolded prion.
“All mammals have prion proteins. We think they help process copper and other metals in the body and they serve an important function in nerve cells. In the case of CWD, a prion becomes misshapen. When that misfolded prion comes into contact with a normal prion, it too becomes misshapen.
“Those deformed prions begin to accumulate in the gut before moving into spinal tissue and eventually to the brain and lymph tissue. Once there they begin to clump together and kill healthy neurons. The disease is fatal 100% of the time.”
Schwabenlander said deer have no natural defense against the disease because their bodies can’t differentiate between normal and misfolded prions. Infected animals release those prions into their environment through saliva, blood, urine and feces.
Linda Glaser works as a senior veterinarian for the Minnesota Board of Animal Health. Her work focuses on farmed deer, elk and other livestock, and oversight of the animal health database.
“Captive cervids are considered livestock under Minnesota statute,” Glaser said. “And they’re the most regulated livestock in the state. Movement of animals between facilities is documented to track potential movement of CWD and other diseases from one herd to another.
“When CWD is detected in a herd the rest of the animals are put down. In 2019 the state legislature gave the agency the authority to depopulate infected herds even if funding isn’t available to buy the animals. So far, though, this authority hasn’t been used.”
Currently, there are 308 captive cervid herds in Minnesota spread across 70 counties. Most contain white-tailed deer or elk, but other species like mule deer, reindeer and Sitka deer also are present in low numbers.
Joni Scheftel is the State Public Health Veterinarian and Supervisor of the Zoonotic Diseases Unit at the Minnesota Department of Health. In that position, she works on diseases and issues at the intersection of human health and animal health — including CWD.
“CWD is a transmissible spongiform encephalopathy or prion disease similar to scrapie in sheep or mad cow disease found in cattle,” Scheftel said. “Unlike other TSEs, though, the misshapen prions that cause the disease can be found in the muscle and fat tissue of the infected animal.
“Even after decades of testing, there has never been a documented case of CWD in humans. Compared to diseases like mad cow disease, though, the sample size has been very small. We don’t recommend that anyone consume meat infected with CWD or from any animal that appears sickly.”