Tuesday, February 4, 2020

Fact Check: Do Wolves Help Spread CWD?

If you went to the website of an opponent to the Colorado wolf reintroduction, you would read in big font: “It’s likely that wolves will be a vector for Chronic Wasting Disease.” Is this true or is this misinformation?

To bolster their claim that wolves will likely spread CWD—an always fatal disease among elk, deer, and moose—the opponents quote from a study done with coyotes and published online in December of 2015. The coyotes were fed CWD-infected elk. The coyotes' feces was found to contain the prions (an abnormal form of proteins) that cause CWD.

The opponents of reintroduction then added a couple of quotes on their website that would lead a reader to believe that coyotes could feed on a CWD-infected animal, leave the carcass, travel miles away, deposit feces, and thus spread CWD. So the reader could then make the leap that if coyotes can spread CWD, surely wolves could too.

Did the opponents tell the whole story? I found the study. Here’s what they left out. 

The 2015 coyote study reports that while CWD had spread to 21 states, how it spreads is not clear and methods of spreading may vary. The report states, “Several human behaviors, such as movement of captive cervids [deer, elk, moose] and the dumping of CWD-positive carcasses from hunter kills in CWD-negative regions, have likely contributed to the expansion, but may not explain all incidences.”

The scientists considered other ways CWD might spread such as by scavengers. The scientists referred to recent work showing that the prions that cause CWD could be passed in the feces of crows. That being the case, the scientists wondered if coyotes could pass infectious prions in their feces. The scientists fed the coyotes a concentrated dose of prion-infested elk brain tissue and found that the coyotes could pass infected material for at least three days after eating. 

But the scientists remind the reader that “In the wild, coyotes would opportunistically consume a wide variety of tissues from a kill or scavenged deer or elk carcass, likely making their actual ingested infective dose much smaller. This study was not designed to mimic a naturally consumed dose of CWD, but rather as a proof of concept to determine if infectivity could pass into coyote feces. ” The study did not say that wolves would likely pass CWD.

Is there other evidence that predators, especially wolves, spread CWD?

Consider this. In January of 2020 the state of Montana’s Environmental Quality Council—composed of state senators and representatives—held a meeting to learn about CWD and help Montana devise a plan to fight the recently arrived disease. The EQC started their full day of study by questioning four CWD experts. 

Representative Gunderson from Libby, Montana, asked, “Do predators spread CWD?”

Dr. Michael Miller, a senior wildlife veterinarian for Colorado Parks and Wildlife, answered, “We certainly haven’t seen any evidence of that.” 

He referred to a study which showed that scavengers, such as coyotes, when fed a large quantity of prions, do pass some prions out the other end of the digestive track. He added that theoretically if the coyotes moved some distance away after eating from a CWD-infected carcass, they could spread the prions. 

The study he refers to is most likely the same study the opponents quoted to support their contention that wolves will spread CWD. It is the only such study that I found through an online search. Additionally, Dr. Miller is cited as a reference in the study’s December 2015 publication.

But Dr. Miller went on to tell the EQC more about the prions that coyotes pass, “But a lot of that infectivity [the ability of the prions to infect other animals] is actually degraded as it passes through their digestive tract. That part of the story doesn’t always seem to get reported.” (That part was not reported on the reintroduction opponents’ website.)

He then added that there’s a fair chance predators are “actually helping to reduce infection in environmental contamination by consuming carcasses and digesting at least a lot of the prion’s infectivity that’s in them.”

Dr. Miller concluded by stating there is “…no indication in Colorado that movements of predators have contributed to the spread of the disease…”

The same question was asked to Hank Edwards, Wildlife Health Laboratory Supervisor, Wyoming Game and Fish Department. He obviously knew Dr. Miller and told the EQC that Dr. Miller did a good job of answering the question, and that he agrees with him.

Both experts have had a lot of chances to study the disease. Colorado and Wyoming have a lot of CWD-infected animals and a lot of predators. In fact, the coyote study notes that CWD was first identified in Colorado in 1967.

Combining information from the coyote study with comments from two CWD experts, I conclude that coyotes could theoretically contribute to the spread of CWD. But in real life, predators, including wolves, in Colorado and Wyoming have not contributed to the spread of CWD. 

In other words, it’s NOT likely that wolves will be a vector for Chronic Wasting Disease. 


Rick Lamplugh writes and photographs to protect wildlife and wild lands.

His bestselling In the Temple of Wolves; its sequel, Deep into Yellowstone; and its prequel, The Wilds of Aging are available signed

His books are also available unsigned or as eBook or audiobook on Amazon.

For Further Information:

To read the coyote study published online 12/4/15 

To learn more about Dr. Michael Miller: 
A CWD website lists him as an excellent source for credible information about CWD.
Dr. Miller received an award for his work with CWD. The award reads in part, “Mike is recognized internationally as a leading expert on wildlife health issues, particularly chronic wasting disease (CWD).” 

To learn more about Hank Edwards:
He is listed under “Contributors and Reviewers” for the 2018 AFWA Technical Report on Best Management Practices for Prevention, Surveillance, and Management of Chronic Wasting Disease. 

To read the misinformation of Colorado Stop the Wolf Coalition, the group opposing reintroduction:

1 comment:

  1. A clear, persuasive analysis, Rick. Keep up the great work!