For decades, chronic wasting disease has plagued Colorado’s deer, elk and moose herds. While Colorado Parks and Wildlife has been working to manage and respond to outbreaks of the fatal neurological disease, it continues to impact the majority of the state’s deer herds. 

“Currently, it’s not very optimistic, but we’re not in the worst situation either,” said Brad Banulis, Parks and WIldlife’s senior terrestrial biologist in its northwest region, at the agency’s regional Sportsperson’s Caucus in Grand Junction on Tuesday, Feb. 18. “We’re being pretty proactive.” 

Parks and Wildlife’s northwest region includes Jackson, Grand, Summit, Eagle, Pitkin, Mesa, Garfield, Routt, Rio Blanco and Moffat counties.

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In 2019, Parks and Wildlife adopted a 15-year response plan as an attempt to reduce the impacts on its deer, elk and moose populations. The plan set forth guidance for conducting regular testing of herds, thresholds to trigger intervention as well as suggestions for how to control its prevalence.

At the time the plan was written, at least 31 of Colorado’s 54 deer herds (57%), 16 of 43 elk herds (37%), and 2 of 9 moose herds (22%) were infected. Once detected, it can be impossible to eradicate as there are no vaccines or treatments. 

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What herds are impacted? 

Chronic wasting disease impacts all ungulates, however, the prominent concern in Colorado has been for its deer populations. 

Currently, in northwest Colorado, there is only one management area — south of I-70 around the town of Eagle — where Parks and Wildlife has not detected any chronic wasting disease in deer. While the remaining herds have varying rates of disease, the agency estimates that infection rates are above 10% in the majority of the region. 

The rates are highest — rising above 25% — in the White River deer herd that occupies portions of Rio Blanco, Moffat, Routt and Garfield counties, according to Banulis. Prevalence in this population has been steadily increasing since 2017 when it was closer to 12%, he added. 

The Bear’s Ears herd, which occupies a similar range in the northwest, also has seen prevalence rise to between 15% and 20%, Banulis reported.

The deer in Middle Park — where historically herds were “highly productive” and had low disease prevalance — have experienced decreasing populations and increasing rates of chronic wasting disease after a series of bad winters, Banulis said. 

“I don’t know if that’s partially been because of the concentration of animals on winter ranges or if it’s also because, with that population coming down, we’ve been reducing licenses a lot, but even at that we’ve hit into the older population” he said. “The hope would be, that as this population rebounds, maybe we also see a drop in (chronic wasting disease) prevalence.”

For Colorado’s elk herds, while there are more herds with no detection, there is an overlap between where there is high prevalence in deer. 

According to Parks and Wildlife’s 2019 plan, “because the areas of infected elk herds are similar or even the same as for deer, management efforts to reduce prevalence in deer herds are anticipated to also reduce CWD infection in elk, at least in the short term.”

“Reducing prevalence in deer should reduce the number of CWD prions that are shed into the environment that could infect elk and moose,” it adds. 

Banulis reported that while it has been detected in moose in both Wyoming and Colorado, a low prevalence stopped the agency from continuing mandatory testing that had previously been implemented. 

What is known, unknown about chronic wasting disease?

Chronic wasting disease is caused by an infectious prion (or abnormal protein) and spreads primarily by direct contact with infected animals or exposure to contaminated environment. The prion is carried in bodily fluids. 

Prevalence of chronic wasting disease in males is twice as high as it is in females, Banulis said. 

It also has been shown to have a lesser impact on Colorado’s more migratory populations, he added. 

“When animals are concentrated, they don’t move, then you get more nose-to-nose contact, there’s prion deposition in the soils,” he said. “The more those animals are in the same spot, the more likelihood there is for an increased prevalence.”

Once prevalence hits the threshold, the plan outlines several management tools. This includes using hunting license changes to reduce population and density as well as the ratio of males to females in certain herds, conduct hot-spot control, remove motivations for congregation of herds where possible and more. 

However, managing the disease is challenged but what is still unknown about the disease.  

“We’ve been studying this disease for a long time, and there’s still so many questions that we don’t know,” Banulis said.

One of the tools initiated by the plan was more regular testing of animals to fill in the gaps of some of these questions. 

Parks and Wildlife requires mandatory testing of deer hunted in Colorado on a rotating basis. Banulis said that this testing will be back in the northwest deer herds in 2027 and that there will be mandatory testing for elk in 2026. There is no mandatory elk testing this year. If the sample comes back positive for the disease, it recommends that hunters not consume the meat, safely dispose of the carcass and can receive reimbursement. 

According to the agency, these samples help it monitor and manage the spread of chronic wasting disease. Banulis said that while the agency tests areas on a five-year cycle, it has done more off-cycle testing in areas of concern to gain additional information where it can.