Chronic wasting disease (CWD), a contagious and fatal neurodegenerative disease, is the biggest issue threatening whitetail deer conservation in the state of Mississippi.
Speaking at the recent Mississippi Agricultural Industry Council annual convention, John Gruchy, biologist, Mississippi Department of Wildlife, Fisheries, and Parks (MDWFP), provided an update that held the attention of those in attendance — many of whom eagerly anticipate each year’s whitetail deer hunting season. “CWD is a prion disease. Prions are infectious agents which are simply abnormally folded proteins,” says Gruchy. “CWD is in the same family of diseases as mad cow disease.”
Mad cow disease was transmitted as cattle ate feedstock, so that disease was controlled by not allowing cattle access to those feedstocks. “We don’t have that option with CWD and that’s why it is so much more difficult to manage,” says Gruchy. “The real problem with this disease is that it’s not a living disease. A prion does not have DNA. We can’t kill it. The only thing we can do is try to denature it, and scientific literature conflicts on the best way to do that.”
Infectious prions, which are found in saliva, feces, urine, blood, and decaying carcasses, can be shed within six months of acquiring CWD. There is no test currently that can detect the disease in an animal until it has been infected for at least 18 months. “In so many ways, we are still learning about this disease, its symptoms and incubation period,” says Gruchy.
Human health, and other concerns
CWD was first identified in the wild in 1981. Since that time, there have been no reported cases of humans becoming infected from eating meat from infected deer, but the Center for Disease Control and Protection (CDC) recommends having a deer tested before its meat is consumed. “My son harvested his first deer last season, we processed the meat, sent the head in for sampling, and three weeks later received the negative results and we were good to go,” says Gruchy.
The state’s first case of CWD came last February from Issaquena County. “A hunter watched the deer expire and contacted us. We took it to the Mississippi State University Veterinary Research and Diagnostic Laboratory in Pearl, Miss.,” says Gruchy. “The National Veterinary Service Lab in Ames, Iowa, confirmed the deer was positive for CWD. We immediately implemented our CWD Response Plan we have had in place for several years and was just updated last August.”
Five-mile radius circular zones were drawn on maps and a goal of gathering 300 samples from within each of those circles was established. “We collected deer from those areas and didn’t have any additional positives,” says Gruchy. “A CWD zone was subsequently set up, supplemental feeding was stopped, and a carcass transportation ban was enacted.”
Gruchy and the other biologists wondered what they were missing when prior to the 2018-19 deer season another positive was confirmed in Pontotoc County. “That made two positives in our state, but they were geographically 200 miles apart,” says Gruchy. “That was very concerning to our entire team, so we decided to set out freezers at drop off points and allow the public to collect animals during the hunting season.”
The drop off points were successful in collecting hunter-harvested samples. A total of 18 positives were confirmed. Positives were also confirmed in north Benton County. “Since then, we have had only a few positive samples detected out of nearly 10,000 tested during the 2018-19 season, but it’s still too early to draw definitive conclusions about what these confirmed positives mean as they relate to the spread of the disease, or where it’s centered geographically in the state,” says Gruchy. “Hunter-killed bucks seem to be the best ways to accrue samples because of the saliva exchanged through their natural behaviors.”
Other states, disease prevalence and management
Wyoming, Wisconsin, and Illinois have been dealing with CWD for many years. Illinois and Wisconsin had positives in 2002. Wildlife officials in Wisconsin took an aggressive approach of sampling deer and letting hunters reduce the population, but public outcry was high, so that approach was curtailed.
The prevalence of CWD in Wisconsin has gone from 1 to 5 percent, while Illinois’ prevalence remains at 1 percent. “Illinois is trying to manage the deer herd by keeping the herd population low, and they have been somewhat successful,” says Gruchy. “In 2002, in their ground zero area, the Iowa County, Wisc., herd had the highest prevalence in the nation at over 30 percent in does, and 50 percent in bucks. Half of the bucks harvested in that state tested positive.”
The concerning thing for Wisconsin biologists is the number of adult female deer testing positive in Iowa County, the first county where CWD was detected in 2002. “That means 30 percent of their female deer population will die every year without a hunter firing one shot,” says Gruchy. “Thirty percent is our threshold in Mississippi. We do not want to harvest more than 30 percent of our female population or that will risk lowering the overall population.”
Wyoming has been dealing with CWD since 1985. They monitored the disease for several years. Biologists there did not see significant population issues until it reached 35 percent prevalence. At that point, their herd population started declining 10 percent annually. Because CWD is relatively new to Mississippi, most of the data being used to manage the problem comes from lab experiments, and applying information from a lab to a real-world setting in the wild is very difficult.
While the prevalence of the disease remains low, biologists hope to reduce the deer density to minimize the spread of CWD via direct contact. “The problem is magnified when prevalence gets above 20 percent,” says Gruchy. “At a low prevalence, the prions are mainly passed from deer to deer, but at some point, the prions saturate the environment to a level where animals might become infected just from contacting plants or soils.”
What you can do
Gruchy and other biologists encourage everyone to report sick deer when they see them. The MDWFP has developed an app that can be used to forward information, or anyone can call 1-800-BESMART — which is the same number used to report game violations.
Just because a deer looks small in stature or poor in weight does not mean it is infected. The presence of neurological symptoms, like a classic A-frame stance, a lowered head with excessive slobbering, and drooping ears are typical signs that a deer has CWD.
Drop off stations this year will have maps so hunters can include spatial data and/or GPS coordinates about where the deer was harvested or found. “It’s sort of like that old game, Battleship, where you narrow down your opponent’s ships through the acquisition of coordinates,” says Gruchy.
Gruchy knows hunters will play a key role in successfully helping to manage the spread of CWD, and he encourages them all to be mindful of this very concerning problem as another whitetail deer hunting season approaches.