Even though hunters do not seem to be paying any attention to Chronic Wasting Disease (CWD) it’s still out there and with each passing year, the news gets worse. Last year there was a glimmer of hope when a potential vaccine was reported.
However, in November 2015, Dr. Mary Wood, a wildlife veterinarian with Wyoming Fish and Game reported that “We have not observed a protective effect associated with this vaccine.”The magic bullet that everyone hoped for is not there — at least not yet. This was the result after a three-year trial on 38 elk in a research facility in Wyoming. There was a slight glitch at the beginning of this research and the final results won’t be known for a year, but the preliminary data does not give much hope for the vaccine. That doesn’t mean that this research was a waste of time. It could lead to other, more productive research for those looking for an answer to CWD. But for the time being, the possibility of a vaccine to slow CWD is not an option.
CWD is a disease of the brain caused by protein infective agents called prions. Although most biologists view CWD as an enormous threat to deer and elk, hunters don’t seem to give it much thought at all. Politicians who control grant dollars needed for research are not paying attention, too. No one seems to be raising red flags signifying just how damaging CWD could be to the future of hunting. However, they should because we have no effective ways to control CWD.
Prion brain diseases that affect humans such as Mad Cow and Creutzfeldt Jakob Disease are extremely complex and have been the focus of much research for years. Solving the mystery of these human prion diseases has been slow, so it should be no surprise that we haven’t found a magic bullet for CWD. We desperately need a cure for CWD because what you are about to read is rather dismal relative to the future of deer hunting.
“Come on, Dr. Dave, surely you over exaggerate all of this, right” you ask.
Deer get diseases all the time and they live through them and we move on. I wish we could, but ever since CWD first reared its ugly head in Wisconsin in 2002, this disease has scared me relative to the future of hunting. As you read what follows, you will understand my concern.
Since the study I’m about to report was done in Wyoming, let’s look at the CWD situation there right now. The surveillance data isn’t in for 2015, but in 2014 a total of 1,632 deer, elk and moose samples were tested for CWD. Of these, 110 tested positive — 83 mule deer, 12 whitetail deer and 15 elk. These samples came from hunters (86 percent), targeted animals (8 percent) and road kills (6 percent). Since 2005, over 750 moose have been tested and only one has been positive. With CWD being endemic to over half of Wyoming (and spreading all the time) and almost 40 percent of deer in the eastern half of the state with the disease, they obviously have a problem.
Melia DeVivo is a doctoral student in veterinary science at the University of Wyoming and she is nearing the end of her study on the impacts of CWD on mule deer in parts of Wyoming. Her study was designed to see if CWD is impacting mule deer populations by reducing their average lifespan. DeVivo was also interested in genetic susceptibility of mule deer. In other words, are some deer genetically less susceptible to getting CWD?
The study is not complete, but there are some preliminary results, and if what she found in Wyoming for mule deer is anything like what we might find in other parts of the country for whitetails, then it is time to become very concerned.
The following report can be found on www.wyofile.com (a great site for information on CWD in Wyoming). DeVivo studied a population of deer where CWD was endemic southwest of Douglas, Wyoming. In 2002 there were 14,000 deer in that area. In 2014 there were half that number and CWD was the reason. The decline during DeVivo’s four-year study was 19 percent per year. Based on her data, she predicted that if nothing changes, local mule deer herds where CWD is endemic will go extinct in 41 years.
We know CWD spreads two ways; via infected animals and prions contaminating the living environments of deer. We also have a disease that incubates in a deer (or elk) for years with no visible symptoms and they release prions into the soil where they remain viable for decades and are basically indestructible. Eventually, infected deer lose their appetite, walk with heads lowered and drool, then die. Older bucks seem more likely to die from CWD than other deer. Meanwhile the prions in the soil can be picked up in plants that deer eat or can be blown for miles on dust carried by the wind. The good news? you can’t stop it.
During her study, mountain lions were the leading cause of mortality, but CWD was second. One suggestion DeVivo made, which has been implemented, was to reduce mortality by eliminating doe hunting where CWD has a high prevalence. But what about genetics? Are some deer genetically immune to CWD?
It turns out that deer have a key gene at one location with three different combinations of alleles and the deer she studied had all three combinations. Deer that have one of those combinations (SS) get infected at a higher rate than deer with the other two combinations (SF and FF). Most of the deer in her area had this bad combination (SS) of alleles and were 30 times more likely to get CWD than deer with the other two gene combinations (SF, FF). Interestingly, only one of 29 mule deer that were SF got CWD and only 2 of 143 captured deer had FF genotypes. Since the SS deer are more likely to get CWD and when they do they will die, does this mean the overall population will slowly become deer that are SF and FF? DeVivo pointed out that we know nothing about SF or FF deer. Maybe they aren’t good mothers. Maybe they aren’t good fathers. If SF and FF deer are as fit as all other deer, then maybe this is a glimmer of hope for the long term.
There is another interesting idea that other researchers have looked at relative to the spread of CWD via computer models. The theory is that CWD diseased animals might be more susceptible to predation. We know hunters can’t discern a sick CWD deer (at least not often), and thus they can’t focus their harvest on animals that might have CWD. They kill deer, then the DNR tests them, so it’s only after the harvest that we learn that some of the harvested deer had CWD. So, during hunting seasons, the taking of CWD animals is random — hit or miss. But wolves, mountain lions and coyotes might be able to tell whether a deer is sick by its behavior and it’s those animals that are easier for predators to kill. If predators do this often, the suggestion is that predators might suppress CWD emergence or limit prevalence.
In fact, a computer study published in 2011 suggested that wolves and secondarily mountain lions and coyotes, “might be a useful tool for management of CWD.” It’s an interesting thought, but when you get out of western areas where there are lots of wolves and lions, it is doubtful that coyotes will be the answer to the spread of CWD. It hasn’t happened so far and probably won’t. Predators certainly won’t cure CWD.
Does the DeVivo study provide insight into what might happen in areas of the Midwest where CWD has a high prevalence rate? Probably. Will predation slow down the spread of CWD in the Midwest? We do not know nor have a guess at this time. Could there be a gene combination in some whitetails, as there was in her study area, that makes them less susceptible to CWD and if so, could they hang on and over time become the dominant genotypes in an area? We have no idea, but it’s possible. Right now there are lots of questions and very few answers.