A neurodegenerative illness called chronic wasting disease is spreading among deer and elk in our region. Now, researchers at Colorado State University say they’ve found a new way to study the disease -- and another indication that it might eventually become capable of sickening people.
As the Mountain West News Bureau has reported, the disease was originally thought to have started in our region. It’s not caused by a virus, bacterium or fungus, but instead by an entirely different pathogen: a type of protein called a prion. A buildup of the wrong kind of prions can lead to cell death and holes in the brain. Chronic wasting disease currently affects animals like deer, elk, moose and reindeer in at least 26 U.S. states including Colorado, Wyoming and Utah. Earlier this year, it was found in Sweden for the first time. It has also been found in Finland, Norway and South Korea.
“This disease is spreading inexorably in North America, it’s not going away, there’s no known cure. In addition, the fact that this is now no longer confined to North America is extremely worrying,” says Glenn Telling, who directs the Prion Research Center at CSU.
As he and his colleagues wrote recently in the journal PNAS, they found additional evidence that it could jump species barriers, potentially infecting other animals including humans.
Telling and colleagues used special mice, some genetically engineered to mimic elk bodies in certain ways, others genetically engineered to mimic deer bodies in certain ways. They exposed those mice to the same set of chronic wasting disease prions and found that the two sets of mice experienced the disease differently; The elk-like mice got sick more quickly and showed different kinds of lesions in the brain compared to the deer-like mice. Importantly, the scientists also found that the mice were propagating slightly different CWD prions.
“Even though we’ve infected them with the same CWD prion disease isolates, they produce these different outcomes,” says Telling. “In other words, CWD isn't the same when we look at different species.”
Essentially, the finding suggests that even if wild animals get sick from the same source of CWD, different species might end up spreading slightly different versions of CWD, with different potential for infecting even more species.
“From my risk assessment and concern of CWD transmitting -- whether it be to sheep, cattle or humans -- knowing that not every CWD strain is the same is concerning,” says Brent Race, a staff scientist at Rocky Mountain Laboratories in Montana, which is part of the NIH's National Institute of Allergy and Infectious Diseases. Race was not involved in this particular study.
He says other scientists are finding that even animals within the same species might spread slightly different versions of CWD.
“I worry about livestock,” says Race, who raises cattle. “Most large ranchers also have wildlife there and maybe the elk CWD is going to infect sheep more readily than deer CWD and things like that.” Or, he says, the disease could bounce between animals -- say, from deer to raccoons and then back to deer again, each time allowing for a tweak in the disease-causing prions.
“At what point do you get a prion that could infect a human? It’s hard to say for sure,” says Race.
This study and others raise an issue: If researchers want to evaluate the potential human health threat in a comprehensive way, they need to test disease samples from many different animal populations.
“I think we’re at the very early stages of trying to understand how many strains are out there in the wild,” says Telling.
His study also gets at a big question in chronic wasting disease: It’s known that infected animals shed CWD prions in urine, feces, blood and saliva, but it’s unknown how, exactly, which route spreads the disease from animal to animal.
Or, as Brent Race puts it: “Was it because they snorted some in their nose? Was it because they ate some? Did it come in contact with their eyes?”
That question is really hard to study in the wild, a problem that’s led researchers including Race to try to figure out a way to investigate how the disease spreads from within the confines of the lab, primarily by finding a type of mouse in which the disease is at contagious as it is among wild animals.
Telling and his lab seem to have developed a mouse that will do that.
“It’s possible to actually study contagious transmission in a cage of mice for the first time,” says Telling.
Nailing down how it moves from animal to animal could hold hints at how to prevent further distribution.
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUER in Salt Lake City, KUNR in Nevada and KRCC and KUNC in Colorado.