Mandatory testing for chronic wasting disease to be widespread in western Colorado this year

Deer hunters in much of western Colorado should be prepared to comply with a free, mandatory testing requirement for chronic wasting disease this fall as Colorado Parks and Wildlife undertakes what the agency is calling an effort to “test the rest” of the state for the disease.

“In general this year we’re trying to kind of ramp up CWD testing in all the (game management) units we haven’t done yet in the last few years,” said Brad Banulis, Northwest Region senior biologist for CPW.

The continued testing push comes as results from mandatory testing last year showed the disease exists at concerning levels in more deer herds in the state than previously known. It has now been documented at prevalence rates of 5 percent or more for male deer in 18 of the 54 herds in the state, after the results came in from last year’s mandatory testing for rifle-season deer hunters, mostly in eastern Colorado. Prevalence rates top 10 percent for 13 of those 18 herds, and 20 percent for six of them.

Altogether, the disease is known to exist in 33 deer herds in the state, 14 of 43 elk herds, and two of nine moose herds in Colorado. Mandatory testing in the state so far has focused on deer because of its apparently greater prevalence in them and threat to them. CPW officials are looking out for when prevalence rates among male deer, which tend to be infected at higher rates than female deer, top 5 percent. When it crosses that threshold, the agency takes actions that can include increasing buck licenses to reduce their numbers.

Last year’s testing focused on 16 herds. Eleven were found to have prevalence rates above 5 percent, and four of those 11 had rates well above 20 percent.

Colorado Parks and Wildlife officials teamed up with the City of Boulder Open Space and Mountain Parks Department to study mule deer in the Table Mesa area of southern Boulder. CPW is focused primarily on chronic wasting disease prevalence and the deer were fitted with GPS collars to study resource use, movement, and mortality. The population size will also be estimated. (Photo courtesy of Colorado Parks and Wildlife).

Matt Eckert, CPW’s terrestrial programs manager, said CPW previously knew rates in a couple of the 11 herds exceeded 5 percent, but in the case of most of those herds it did not.

“Several in the plains did not have data to show prevalence exceeding 5 percent until the mandatory testing effort. Now we now that multiple herds (there) are exceeding 5 percent,” he said.

Testing last year also resulted in the disease being discovered in a couple dozen more of the state’s 185 game management units, though CPW has emphasized that doesn’t necessarily show it’s spreading. Rather, it means it has been demonstrated to exist in areas where there previously hadn’t been enough testing to show it was there.

While most of the units where it was newly found were in eastern Colorado, it also has now been found in units 41 east of Grand Junction, 52 north of Hotchkiss, 444 southeast of Glenwood Springs, and 32 in the Roan Plateau region west of Rifle. Those areas didn’t have mandatory testing last year. But test results can come from testing requested by hunters, or cases involving road kill or animals put down after being suspected of having the disease.

Altogether, CPW got test results last year for more than 7,700 samples for deer, elk and moose.

The disease was first identified in captive deer in a research facility in Colorado in the 1960s, and was found in wild deer in northern Colorado by the 1990s and Western Slope herds in the early 2000s.

CPW imposed mandatory testing in the early 2000s but didn’t again require testing in some areas until 2017.

Mandatory testing that year for the White River deer herd in the Meeker area showed a disease prevalence of 15.3 percent. Testing in 2018 for the Bears Ears herd farther north showed prevalence topping 18 percent. Combined, the White River and Bears Ears populations account for about a fifth of all mule deer in the state.

The agency has prioritized mandatory testing to date in areas of highest priority and concern, focusing on larger herds and areas where the infection rate has been thought to be highest. Now it is trying to test primarily in areas not previously subject to mandatory testing so it can achieve a statewide understanding of what the disease is doing.

This fall it will require testing in areas such as southwestern Colorado, the Salida region, Grand Junction areas including Glade Park/Piñon Mesa and the Bookcliffs region, and areas in Moffat and Rio Blanco counties along the Utah border. Especially in parts of southern Colorado, the disease has gone undetected so far or been found at very low levels based on the non-mandatory testing results to date.

While non-mandatory testing has produced some information on the disease’s presence in some areas, mandatory testing over one or multiple years produces enough results to calculate more reliable prevalence rates and guide CPW’s response. While its chronic wasting disease management plan mandates some kind of response where prevalence rates top 5 percent, in some cases wildlife officials have responded with license adjustments where rates are lower, such as in Middle Park and on the Uncompahgre Plateau, in hopes of proactively keeping rates lower and dealing with any localized CWD hot spots.

“One key misconception is that CWD management will kill off the bucks, that the cure is worse than the disease. This is just not true,” Eckert said during a presentation in May to the state Parks and Wildlife Commission.

Where CPW may adjust hunting license numbers as a CWD response, it still aims to keep buck and doe numbers within the population range targets in local herd management plans.

“Currently we do believe that hunter harvest is the best tool to manage chronic wasting disease,” Eckert told the commission.

A benefit of the mandatory testing is that it’s free, as opposed to the $25, still-subsidized cost CPW charges for hunters who voluntarily participate in the testing program. Free tests also will be offered for hunters harvesting deer in muzzle-loading, archery and other seasons other than rifle seasons where mandatory testing is in place this fall.

Participating in testing, mandatory or not, can provide hunters peace of mind by making sure a deer is free of chronic wasting disease before they eat it, while also helping CPW monitor the disease and respond to it. Said Banulis, “We just appreciate hunters helping us contribute to the science and management of our deer here in Colorado.”


Chronic wasting disease is a fatal prion disease affecting deer, elk, reindeer and moose. It causes animals to waste away through dramatic weight loss. Prion diseases involve abnormal folding of cellular proteins in the brain. Other prion diseases include scrapie in sheep and goats, mad cow disease, and in humans, Creutzfeldt-Jakob disease.

CWD prions in feces, saliva or carcasses of infected animals spread the disease through direct or indirect contact with other animals. CWD hasn’t been documented to have ever crossed over to humans. But Colorado Parks and Wildlife advises hunters not to eat animals that appear to have been sick, and to get the heads of animals they plan to eat tested as a precaution because infected animals may not appear ill. The agency also is tracking the disease closely due to concern about impacts on herd numbers and health.


Eighty-nine of Colorado’s 185 game management units will be subject to mandatory testing this fall, mostly in western Colorado. Information on where testing is required can be found on page 22 in CPW’s 2020 big-game rules and regulations brochure, which can be found on the agency’s website.

The requirement applies to either-sex, rifle-season deer harvests. Hunters should bring their unfrozen deer head to any CPW submission location; the agency plans to post a list of those locations this summer on its website. Hunters should leave about 5 inches of the neck on the head, to ensure access to lymph nodes or tonsils needed for tissue sample collection.

Hunters should expect it to take about 15 business days to receive results. CPW ships samples to a Colorado State University laboratory for testing.

Where tests come back positive, hunters can’t receive refunds for their licenses but can be refunded for meat-processing costs they have incurred, with some limitations.