Once steady, Chronic Wasting Disease on the rise in the Black Hills

What’s different about the Black Hills? That’s a question wildlife biologists don’t yet have an answer to, but it could prove significant in the fight against Chronic Wasting Disease (CWD).

“The Black Hills is really unique,” says Hank Edwards, Wildlife Health Laboratory Supervisor for Wyoming Game & Fish. CWD was identified here in the early 2000s, but then “nothing happened.”

In other parts of Wyoming, cases of CWD began to increase pretty dramatically after it had been identified; reports indicate that some areas, such as around Yellowstone National Park, are now seeing significant growth, not long after the disease was first detected.

“We expected that to happen in the Black Hills, and it didn’t,” Edwards says.

It’s only recently that the prevalence of CWD in northeast Wyoming seems to be on the rise, despite the dense populations of deer and elk. That could make this part of Wyoming an area of interest as scientists work to learn more about the fatal disease, which affects deer, elk and moose and is caused by abnormally folded proteins called “prions”.

Scientists are not sure that CWD can spread to humans or livestock, but it’s tough to be certain about any aspect of the disease at this stage, says Game Warden Chris Teter.

“There are just so many unknowns about prion diseases like CWD. There’s so much research that has yet to show us what we can do, if anything, about it, and even how it’s spread,” he says.

The difference between the Black Hills and other affected areas could mean there is value in evaluating the region and the specific herds that call it home.

“We’re in the process of doing that, as well as comparing management styles through Wyoming and Colorado and Alberta – many of the western states, just to see if there’s something we’re already doing that’s making CWD maybe worse, or actually affecting prevalence and we don’t know it. We’re just starting to look at that,” Edwards says.

But right now, Game & Fish doesn’t know what makes the Black Hills different. This area is particularly productive when it comes to deer, so a high percentage of the population is harvested come hunting season. Is that why CWD took it’s time to spread?

“Maybe that’s having an effect. Who knows,” says Edwards.

CWD tends to be tied to certain clay soil types, in which the disease can bind, but the Black Hills doesn’t feature a lot of those soils. “Is that having an effect? Maybe, we don’t know,” Edwards says.

Other areas of the state are seeing high prevalence despite lacking these soils, “But that doesn’t mean there isn’t something unique about the Black Hills we don’t know about.”

CWD is slow-moving. At this point, says Edwards, we’re probably still early in the course of the disease.

“It’s really hard to tell whether this is just an individual response from this particular herd, or whether this is how the disease progresses and we just don’t know that yet,” he says. “There are probably many reasons, so there’s a lot we need to learn about this disease and how herds respond to it.”

Sample Sizes

In 2016, 98 samples of whitetail deer were taken from the Black Hills herd unit, which consists of deer hunt areas 1 through 6. Only one was positive – a prevalence rate of less than 1%.

“It’s interesting because, for a long time, our prevalence was very low,” says Teter. “But in the fall of 2018, it seemed like we found some hotspots because prevalence increased, particularly west of Sundance in deer hunt area 3.”

To make best use of its limited personnel and resources, Game & Fish is now concentrating on sampling for CWD in certain areas on a rotating basis. The idea is to get more valid sample sizes, says Teter, rather than smatterings from across a wide area.

In 2018, when the Black Hills was last under surveillance, a sample of 130 male mule deer returned nine positives, which means the prevalence rate had risen to around 7%. Seven of 106 samples from male whitetail deer came back positive, a prevalence rate of 6.6%.

“When you sample for CWD, you really do need good sample sizes. As we’ve modified our sampling protocol, we’re looking for 200 samples from each herd unit. We figure that’s about what it takes before you have any confidence in your prevalence levels,” says Edwards.

“Our surveillance rotates. About every five years we hit different herd units because we don’t have enough personnel or lab capacity to get good, meaningful sample sizes from every herd unit around the state.”

Because of this strategy, only eight samples from mule deer bucks were tested in 2019 and none came back positive for the disease.

“The problem is that, until we have good sample sizes over time, it’s really hard to say that prevalence is increasing. That said, yes…it does appear that prevalence is increasing,” Edwards says.

A Spreading Problem

CWD is a nationwide issue in terms of its implications for wildlife management, says Teter. Whether or not fears about transference to humans turn out to be founded, he adds, hunters are also understandably concerned.

“The big concern in the western part of the state is if it shows up in those areas where there is an elk feeding ground,” Teter says.

In Wyoming at least, the evidence suggests that CWD is generally on the rise. “There are many areas in the state, particularly down around Glenrock and Wheatland, where the prevalence is much higher than it is in the Black Hills, but it seems like CWD is almost anywhere you look for it very hard,” Teter says.

Positive samples have now been confirmed in elk, whitetail and mule deer in Crook County. While research is ongoing to investigate the disease and perhaps find a treatment, Game & Fish will continue to offer a sampling service to the public during future hunting seasons.

“People are certainly welcome to submit their own samples to the state veterinary lab. There is a fee associated with that,” says Teter. Information is available on the Game & Fish website explaining how to take and submit a sample.

Meanwhile, if you encounter an animal that you suspect may be suffering from CWD, the game warden would like to hear from you.

“I’m always interested in any wildlife that is displaying unusual behavior or symptoms,” says Teter.

While deer and elk may display no symptoms at all at first, CWD in its advanced stages can lead to droopy ears, a lack of energy, a lack of gloss to the coat and lethargy.

“In extreme cases, they become really emaciated, too,” he says.