Since chronic wasting disease, or CWD, was detected in Montana’s wildlife in 2017, the affliction has become increasingly widespread. Though the CWD positivity rate among all deer, elk and moose sampled in the state remains in the single digits, there are parts of the state where enough animals — namely white-tailed deer — have tested positive for CWD that wildlife managers are concerned about population declines like those seen in southeast Wyoming. This CWD primer explains the cause and effects of CWD, what’s being done to combat it, and how hunters can help wildlife managers limit its spread.

WHAT IS CHRONIC WASTING DISEASE?

Chronic wasting disease is caused by misfolded proteins that cause neuropathy in cervids. White-tailed deer, mule deer, elk and moose can develop CWD, a form of transmissible spongiform encephalopathy that’s related to Mad Cow Disease. It’s 100% fatal, very persistent once established in an area, and easily transmissible via contact between animals and their bodily fluids and excretions. The misfolded proteins, called prions, that cause CWD are most prevalent in the brain and spinal tissue of an infected animal, but are widespread throughout its body. It causes organ damage and eventual death. Infected animals in later stages of the slow-acting disease appear sickly and malnourished, hence the name.

HOW PREVALENT IS CWD IN MONTANA?

Fewer than 3% of the nearly 19,000 cervid samples FWP has tested in the past four years have come back CWD-positive. The majority of the 469 positive samples were obtained from white-tailed deer. As of Oct. 26, one elk, three moose, 123 mule deer and 342 white-tailed deer statewide have tested positive for CWD during that four-year span. It’s been found on the Blackfeet and Fort Peck reservations and in 27 of the state’s 155 hunting districts, or about 17% of hunting units statewide. Though it hasn’t been detected in central Montana, there are pockets of the state where up to 24% of the animals submitted for testing were carrying the disease — rates high enough to worry game managers about population declines. Just three of the state’s hunting districts — units 100 and 104 in the far northwestern corner of the state, and unit 322 east of Dillon — account for more than 60% of all positive samples. 

DO HUNTERS  NEED TO DO ANYTHING DIFFERENTLY THIS YEAR?

The state Fish and Wildlife Commission passed two regulations this year to help limit the spread of CWD, one centering on carcass disposal and another pertaining to masking scents. FWP is also ramping up sampling efforts in regions deemed Priority Surveillance Areas, hunting units where the department is particularly invested in monitoring disease spread.

Since the prions that cause CWD can persist in the environment — including soil and vegetation — for years, wildlife managers urge hunters to practice safe carcass disposal.  “If you kill an animal and you’re not going to be processing it somewhere else, the best thing to do is leave the brain and the spinal tissue on site — just leave it right there,” advises FWP Game Management Bureau Chief Brian Wakeling. Hunters who remove a carcass from the field are instructed to first bag all carcass parts, including the brain, eyes, spleen, lymph gland and spinal cord, and dispose of them at a Class II landfill. Most municipalities have one. FWP notes that dumping carcasses is illegal, unethical, and can spread diseases like CWD. 

Since the prions that cause CWD can be present in an infected animal’s bodily fluids, the commission recommends against the use of masking scents, e.g., deer urine, unless they’ve been responsibly sourced. Artificial scents are the safest option, FWP says, but hunters who prefer animal-derived scents are advised to use only products that have been cleared by the Responsible Scent Hunting Association. Products with DPPü or RtQUICü labels are approved for use in the state.

FWP’s educational materials on CWD note that hunting is the primary tool the agency uses to monitor and manage the disease. “Concerns over CWD shouldn’t stop you from enjoying hunting season,” the department counsels. FWP is asking people who’ve harvested a deer, elk or moose, especially within a Priority Surveillance Area, to have the animal tested for CWD. The testing program is free and voluntary. 

CWD Priority Surveillance Areas, sampling locations, and carcass disposal sites.

HOW DO I GET AN ANIMAL I’VE HARVESTED TESTED?

FWP has 25 sampling locations around the state where hunters can have their kills tested, including all FWP regional headquarters, which are serving as sampling sites through the big game hunting season. The sampling locations are concentrated in areas where CWD has already been detected, but they span the state from Libby to Miles City.  

Hunters can either take an animal’s head to one of those sites and ask FWP personnel to extract the sample, or collect the sample themselves and drop it off. Hunters also have the option of mailing samples to FWP’s Wildlife Health Lab in Bozeman for testing. Hunters who opt to collect a sample themselves will need to remove the animal’s lymph nodes and keep them cool, but not frozen. Guidance for doing that is available in this video

Once a sample has been submitted, FWP will post test results online. The department aims to deliver results within two weeks, and ideally sooner, Wakeling said. Last year the average turnaround time was about seven days.

IS IT SAFE TO EAT AN ANIMAL THAT’S TESTED POSITIVE FOR CWD?

Both the World Health Organization and the Centers for Disease Control advise against consuming an animal that’s infected with CWD. Wakeling said there are no known cases of humans developing CWD after eating an infected animal, but noted that was once true of Mad Cow Disease, which like CWD is a form of transmissible spongiform encephalopathy. Mad Cow Disease jumped the species barrier in the mid 1990s, causing at least 20 Britons who consumed infected cow meat to develop a variant form of Creutzfeldt-Jakob Disease, a slow-acting degenerative brain disorder that’s ultimately fatal.

“Having said that,” Wakeling added, “I’m sure thousands of hunters have consumed [CWD-infected meat] over the years and there’s no evidence that it’s causing any issues with human beings.”

MY ANIMAL CAME BACK POSITIVE. NOW WHAT?

Hunters who harvest CWD-positive animals can request a replacement tag from FWP. To be eligible for the replacement tag, they must surrender the entire infected animal to the department, including the head. The replacement tag is good for the same season only.

HOW AND WHEN WAS CWD INTRODUCED TO MONTANA?

CWD was first detected in the state in 2017. The source of the infection hasn’t been definitively determined, but CWD has been present in neighboring states and Canadian provinces for decades. It’s widespread in Wyoming, where it was detected in the wild in the 1980s. Biologists in Saskatchewan first found CWD on a game farm there in 1996, and in the wild in 2000. As of 2021, 26 states and three Canadian provinces have identified CWD among wild or captive cervid populations.

Wakeling said that though CWD is detected more frequently among captive cervids, it can’t be definitively traced to game farms. “A lot of people point their fingers at the captive industry, and there’s certainly been some of that that has occurred, but to say that was the source of exposure in Montana is simplistic,” Wakeling said. “It’s probably not the only answer.”

IS THERE A CURE?

No. Most agencies and researchers agree that it’s impossible to eradicate the disease once it’s present in a population, and there are no treatments for CWD. “It’s not a bacteria, it’s not a virus — it’s a misfolded protein — so it’s not like you can develop a vaccination,” Wakeling said. “It’s a different critter altogether.”

That said, the agency is deploying management tools to prevent it from spreading into areas that haven’t produced a CWD-positive sample.

WHAT IS FWP DOING TO SLOW ITS SPREAD?

This spring the Legislature bumped up FWP’s funding for wildlife disease surveillance and response by $756,816. Three-quarters of that funding is derived from firearm and ammunition taxes collected under the Pittman-Robertson Act, and the remaining 25% comes from general hunting license fee collections. 

The agency’s strategy is to monitor CWD’s distribution in the state, limit its spread through educational campaigns, and use targeted hunts to reduce its prevalence among infected herds. Wakeling said studies have shown that bringing down the overall population of an infected herd and reducing the number of bucks can slow transmission rates. He said that’s especially true of mule deer bucks, which tend to range farther and come into contact with more animals than their female counterparts.

If the department notes an increase of positive samples in an area, it can increase harvest quotas within specific management zones or hunting districts. Last year FWP issued special CWD hunts in all or parts of nine hunting districts in Region Three in southwest Montana. 

“We took that to the commission [and] did that in a very public process to try to make sure that everybody was aware of [the situation] and the commission was well-informed,” Wakeling said. “That’s likely the approach we would continue to use.”

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Billings native Amanda Eggert covers environmental issues for MTFP. Amanda is a graduate of the University of Montana School of Journalism who has written for Outside magazine and Outlaw Partners. At Outlaw Partners she led coverage for the biweekly newspaper Explore Big Sky. Contact Amanda at aeggert@montanafreepress.org.