A 13-year study at Rocky Mountain Laboratories in Hamilton found no evidence that Chronic Wasting Disease can bridge the species barrier between cervids like deer to a species of monkeys genetically similar to humans.
While that news may provide some comfort to Montana deer hunters, one of the chief scientists of the study said people need to remain cautious when processing or consuming wild game.
“At the end of the day, macaque monkeys are not humans,” said Brent Race, a RML veterinary staff scientist.
The deadly prion-based disease was discovered for the first time in the state last fall in deer herds in eastern Montana along both the southern and northern borders. The always-fatal disease is caused by a misfolded protein that impacts the brain.
CWD was first identified in 1967 in captive deer held in a Colorado wildlife facility. The disease has slowly been spreading across the country and into Canada since then. It’s now found in 25 states.
While there has never been a documented CWD case in humans, a similar prion-based disease did jump from one species to another in the 1990s when Great Britain’s Mad Cow epidemic nearly collapsed that country’s cattle industry and killed more than 200 people in England and Western Europe.
Race’s father, Richard, was one of the RML scientists who began exploring the risks of the disease to humans in the late 1990s in a study using two different species of monkeys.
As part of that study, 14 macaque monkey were exposed to brain matter from CWD-infected deer and elk either through direct injections into the brain or orally using feeding tubes. The last macaque was euthanized in the fall of 2016.
RML researchers wrote three peer-reviewed scientific papers on the study, including the latest that was published last week in the Journal of Virology. In each paper, the scientists reported finding no sign of CWD in the macaques.
In the most recent study, researchers added eight macaques that had not been inoculated with CWD and used a new, ultra-sensitive technique for detecting prion diseases that was developed at RML.
“We came away even more confident in our findings,” Race said.
The RML study follows an announcement last year by a Canadian-German research team that said they documented transmission of the disease from CWD-positive deer meat to macaque monkeys. That study has yet to be published in a peer-reviewed publication.
“I feel very confident that we didn’t see any transmission of CWD in our study,” Race said.
Race served on the Montana Fish, Wildlife & Parks’ citizens’ advisory committee that helped develop the state’s CWD response plan.
In deer, the disease appears to spread through social interaction of nose-to-nose contact. Deer also shed the CWD prions in urine, feces and saliva. Carcasses are also a reservoir for the disease, which can remain viable in the environment for years, if not decades, Race said.
The state conducted late hunts last year in Carbon and Liberty counties. Of the 400 deer tested during both the regular and special seasons in Carbon County, 10 tested positive for the disease. None of the 121 deer tested in Liberty County had the disease. The only positive test there came from a collared mule deer that was shot during the regular season.
Race said there is no reason to believe that CWD won’t continue to spread through the state, but hunters can make a difference in slowing that spread by correctly disposing of deer and elk carcasses.
“There’s not a lot of geographic features that will stop it from spreading,” Race said. “We will have Chronic Wasting Disease here for the rest of our lives.”
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