Report highlights mountain lions’ role in controlling chronic wasting disease spread

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Proponents of ‘Trophy Hunting’ ban cite report from experts

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A deer with late-stage chronic wasting disease. Photo courtesy Cats Aren’t Trophies.

Supporters of a ballot initiative that seeks to ban the hunting of mountain lions, bobcats and lynx are citing a recently-released report saying mountain lions play a critical role in reducing the spread of a fatal, incurable neurological disease affecting deer and elk. 

According to the report “Big Cats as Nature’s Check Against Disease” by Dr. Jim Keen, a veterinarian and infectious disease expert, mountain lions prey on deer and elk afflicted with chronic wasting disease, an illness caused by proteins called prions and spread through urine, feces, saliva, or contact with a contaminated environment.

Symptoms of the disease include behavioral changes, weight loss, tremors, confusion, teeth grinding, and drooling. The disease has a 100% fatality rate.

The Teddy Roosevelt Conservation Partnership, a nonprofit organization dedicated to increasing federal funding for conservation and preserving access for hunters and fishermen, called chronic wasting disease “the biggest threat to the future of deer hunting.” 

“With no vaccine or cure for Chronic Wasting disease, wildlife managers are struggling to find solutions,” Keen said.

“Perhaps the best policy response at the moment in Colorado is to stop killing 500 or so mountain lions a year that conduct population cleansing at no cost to the state and that protect the long-term health and viability of cervid populations.”

The report also references field studies conducted in Colorado suggesting that coyotes, mountain lions, and bobcats can inactivate the prions that cause chronic wasting disease during digestion, reducing environmental contamination. According to the report, if not ingested by a predator, prions can survive in an environment for years. 

Banning the hunting of big cats will benefit the deer hunting industry by reducing the spread of chronic wasting disease, Keen also claimed. 

“If you want to protect hunting and other forms of wildlife-associated recreation associated with deer and elk, then protect mountain lions and allow them to deliver their gratis predator-cleansing services,” said Keen. “Mountain lions are a deer and elk hunter’s best friend.”

Some wildlife experts, however, are unsure whether mountain lions significantly impact the spread of chronic wasting disease in deer and elk populations. 

Larry Desjardin, president of the conservation nonprofit Keep Routt Wild, said he used to believe mountain lions “could be the key” to controlling the disease, but has since changed his position on the matter. 

According to Desjardin, mountain lions tend to prey on CWD-positive deer in the later stages of the disease’s progression, when it has become strongly symptomatic. However, for most of the disease’s progression, which can take up to two years before becoming fatal, the infected deer or elk show no symptoms but continue to shed infectious prions, which can spread to other animals.  

“There is no evidence that areas with large lion populations have significantly fewer CWD infected deer,” said Desjardin. “Thinking of the extreme case is a good thought experiment about this mechanism- imagine that lions selectively cull all CWD-positive deer one day before they were going to die anyway. Of course this would have no impact, as the vast majority of prions would already be shed.”

Desjardin says hunting is the only tool shown to impact CWD levels in mule deer, because the disease occurs at a much higher rate in males, and a study where hunters were issued more tags for bucks than does showed a subsequent drop in CWD.

“I once advocated for a reduction of lion tags in a local game unit to grow the lion population and therefore reduce CWD,” said Desjardin. “In retrospect, I was wrong. I learned about the timing of lion culls by studying more literature. It’s up to all of us to follow the science and look for realistic methods that could control this terrible disease.”

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