June 23, 2022
Ribs and hip bones press against the hide, showing the detailed design of the skeleton within. The malnourished buck takes one stiff-legged step at a time, unaware of where it is, unsure of where it’s going. It shakes, shutters and shifts its head from side to side. Then, it lies down, draws one ragged last breath and never stands back up.
That deer didn’t die from old age. It succumbed to chronic wasting disease (CWD). The latter stages of CWD are cruel. It’s quite similar to Creutzfeldt-Jakob disease in humans, and for those unfamiliar, the outward effects can be likened to dementia.
While the buck died directly from CWD, few deer make it that far. This disease is debilitating and diminishes the host’s ability to evade predation and hunting. While few CWD-positive carcasses are found on the landscape, many of the deer killed in other manners—including by predators, hunters, vehicles, etc.—wouldn’t have died if not for the effects of this disease that greatly hinders their cognitive and physical abilities.
"Chronic wasting disease is the biggest threat to deer and deer hunting in North America," said Krysten Schuler, PhD, wildlife disease ecologist and co-director of the Cornell Wildlife Health Lab. "While our generation may only see the spread, our children and our grandchildren will see the repercussions.
"Today’s deer hunters are resistant to changing cultural traditions, but if we don’t take action, we will lose the overall war. Just because you aren’t seeing dead deer in the woods doesn’t mean that it’s not an issue."
CWD Is Leaping Forward
Once contracted, CWD is an always-fatal disease. It can take months or years before deer begin showing symptoms, but rest assured, it’s a death sentence. And it’s spreading rapidly.
Take Texas, for example. In 2021, CWD took a huge leap forward. As a result, researchers GPS-collared 30 9-month-old mule deer in a newly established CWD containment zone. They hoped to determine just how much yearling deer dispersal impacted spread.
"CWD is expanding throughout the country resulting in an increasing need for adaptive management," said Calvin C. Ellis, a graduate research assistant at Caesar Kleberg Wildlife Research Institute at Texas A&M University, Kingsville. "We still have much to learn about CWD, affected species, predicting spread and active management. Further research is needed to reduce impacts globally."
Arkansas is another model for rapid CWD spreading. "Surveillance for CWD in Arkansas began in the late 1990s and several preventative measures were put into place in the early 2000s," said Dr. Ballard Jorge. "CWD was first detected in the state in 2016. Unfortunately, at that time, the disease was already occurring at a high prevalence in the Upper Ozark Region and had likely been present in the state for several years. Since 2016, the disease has been detected in 19 counties in the state. Five counties in the upper Ozark region continue to demonstrate a high disease prevalence, with the rest of the affected counties demonstrating much lower prevalence."
Some might suggest CWD hasn’t been spreading rapidly, but has been a slow progression. If spreading naturally via deer-to-deer contact alone, that’s generally true.
"CWD generally follows logistic growth," Ellis said. "Logistic growth is characteristic of increasing disease prevalence, where we see an initially low number of cases followed by a rapid increase prior to a decreasing rate of increase. If CWD was already long present, test results would show high prevalence with very little increase. Texas, specifically, has seen increasing prevalence throughout the past few years, demonstrating that the state is at an early onset of the disease."
Unfortunately, with the spread of CWD, it begs certain questions. How does it spread? Can we stop it? If not, can we even slow it until a solution is discovered? Several things make this a steep task.
Deer Dispersals, Excursions and Migrations Create New Hotspots
According to Ellis and others, juvenile dispersals, adult excursions and seasonal migrations can impact spread. This emphasizes the importance of understanding and predicting juvenile movement, which will help in predicting and managing disease spread.
Interestingly, in the first year of Ellis’ and others’ research, approximately 27 percent of juvenile mule deer made large-scale movements. Of those, some were complete dispersals (meaning no return trip), and others were excursions (meaning round trips).
"Our most interesting observation was of two females that made an 82-mile excursion over a couple of months," Ellis said. "One of the females, Red 10, made this movement in two 41-mile segments, and completed each in less than week. Her counterpart, Red 25, made the exact same movement, but took almost a month per segment despite leaving at the same time. Often, males are the most likely to disperse. However, 37 percent of the movements we examined were by females."
Obviously, this is natural deer behavior that can, and does, impact the spread of CWD. It’s a factor you can’t control. Furthermore, it becomes even more complicated to account for along state lines, where management plans on either side oftentimes conflict.
Humans Are CWD Super-Spreaders
If CWD spreads slowly, it begs the question, why are there pockets of CWD throughout the country and not a gradual wave of progression from the original source? While natural, deer-to-deer spread is happening in many places, it isn’t the only—or even primary—concern. A troublesome truth is that humans, particularly hunters, are indirectly facilitating the spread.
"CWD spread is most likely being facilitated by humans," Ellis said. "If spread occurred exclusively through animal contact, we would likely see a gradual progression wave as infected deer travel throughout the landscape. However, humans are coming in contact with prions and spreading them across state lines.
"For example, a hunter could harvest an infected deer and then transport the carcass back to their home to process it, clean the skull, etc., and be unknowingly spreading prions, which can persist on the landscape for years. This human-induced spread is likely why we are seeing these seemingly random CWD pockets pop up, and stresses the importance for incorporating animal movement and human influence into disease modeling. There are many actions we can take to reduce human-facilitated spread."
Game farms are super-spreaders, too. "We have seen trace-out from CWD-positive deer breeding facilities result in multiple exposed counties," Ellis said.
Schuler concurs and stresses the importance of ensuring that commercial operations with captive cervids aren’t worsening the issue. Everyone must be on board with CWD management. It’s important for the state agencies and other organizations combatting this disease to have the support of all hunters and wildlife managers, even those being classified and handled as livestock. Even then, additional resources and tools are needed to do so effectively.
"This issue goes far beyond native cervid populations; much of the revenue produced by deer hunters is used to manage a variety of game and non-game species, which may also be negatively impacted if CWD begins to affect hunter participation," Jorge said.
Researchers are working around the clock to better understand the disease, and to fight back. Ellis, Jorge and Schuler are among many who are working toward the common goal.
"We have a large research effort, called the Surveillance Optimization Project, that stretches across the eastern half of North America and looks at maximizing efficiency and effectiveness of CWD surveillance in white-tailed deer," Schuler said. "With this effort, we can use ‘big data’ to identify how states and provinces can best sample. By sharing information across borders and using computer-based artificial intelligence techniques, we can make sure states are doing the best sampling they can for the least expense. Surveillance costs the states a lot of money and we need to figure out how to do it better, whether that’s through different tissues, testing or strategies."
Jorge says another great project began in 2016. Interestingly, it revealed eight genetically distinct subpopulations of whitetails in Arkansas alone. It is information like this that will help biologists find potential clues and solutions on deer movement and disease spread.
Overall, there is much good work being conducted by the Arkansas Game and Fish Commission, the National Park Service, the Mathiason Lab at Colorado State, the United States Forest Service, the Southeastern Cooperative Disease study, the University of Georgia and many others. The bulk of the current CWD research is looking to accomplish certain things, including:
- Determine how the disease impacts deer behavior.
- Develop effective disease management programs.
- Create tools that limit the spread of CWD.
- Slow the spread of the disease.
- Predict future trends in deer populations.
- Create an effective CWD test for hunters to use on their harvests.
- Produce better large-scale testing procedures.
"On the deer side, we have been working to improve state wildlife agencies’ surveillance strategies using a risk-weighted approach, which samples more heavily in areas where CWD is likely to show up and testing, the animals that are more likely to have CWD," Schuler said. "In both Tennessee and Alabama, the highest risk counties were the ones that found disease for the first time. That demonstrates to me that we have the tools to help find the disease. Now we need better acceptance of management options and more preventative measures.
"The upside is that CWD is not everywhere yet, and we can take measures now," Schuler continued. "I’d just like to encourage hunters to be part of the solution. If you don’t have CWD in your area yet, do everything you can to not get it. Prevention costs the least and works the best. If you are in a CWD zone, support the management that’s necessary to stop the disease from spreading."