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Chronic wasting disease doesn't affect humans. Experts say tracking, containment key to keeping it that way

Humans have eaten venison from CWD-infected deer before and did not get the disease, but at a recent Minnesota legislative hearing on this year’s environment and natural resources bill, a leader in the state’s effort to trace CWD said the key to preventing a possible animal-human jump is identifying and slowing the spread.

Chronic wasting disease deer buck
A white-tailed buck in the final stages of the always-fatal chronic wasting disease. A CWD-positive deer was confirmed among deer shot by hunters this fall in the Brainerd, Minnesota, area.
Contributed / Warden Michael Hopper, Kansas Department of Wildlife, Parks & Tourism
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ST. PAUL — There is no evidence that chronic wasting disease, the fatal infection that makes deer resemble the walking dead, can spread to humans. But scientists say the odds of that happening are greater if it is allowed to spread unchecked.

In Minnesota, a group of scientists is working to monitor the spread of the disease, and one of their aims is to prevent animal-human spread from happening. The Minnesota Center for Prion Disease Research and Outreach has developed a test to identify CWD and is conducting surveillance across the state in the fight against the disease, which the Department of Natural Resources says has been identified in 153 deer in Minnesota since 2002.

Nationally the disease has been identified in deer in more than 30 states and four Canadian provinces in free-range and domesticated populations. Most positive cases in Minnesota have been in the southeastern part of the state. The first wild deer in northeast Minnesota tested positive for CWD this spring. State game officials have taken efforts to prevent the spread of the disease including building fences around deer farms where the disease is identified and banning the transportation of deer. St. Louis County has considered a ban on new deer and elk farms.

Humans have eaten venison from CWD-infected deer before and did not get the disease, but at a recent Minnesota legislative hearing on this year’s environment and natural resources bill, a leader in the state’s effort to trace CWD said the key to preventing a possible animal-human jump is identifying and slowing the spread.

“The more exposure that humans have to CWD prions, it is possible that we can see an instance where a human could develop a neurodegenerative disease,” said Dr. Peter Larsen, a University of Minnesota veterinary medicine professor and co-director of the state’s prion research center. “If we can eliminate or reduce prions from entering the food supply with advanced surveillance methods that we can have to help prevent it we don’t need to get to that point.”

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Chronic wasting disease is an illness in deer, moose and elk that destroys the brain and causes the animal to waste away. It’s colloquially known as “zombie deer disease” because of the weight loss and confused, uncoordinated movement deer exhibit before succumbing to the disease.

Chronic wasting disease
This is a deer brain that has been affected by chronic wasting disease. (2002 file / University of Wyoming)

It’s not caused by bacteria or a virus, but instead, by an organic molecule called a prion, an abnormally structured or “misfolded” protein that takes on the properties of a pathogen. Prions are known to cause diseases that destroy the brain such as mad cow disease and scrapie in sheep. There are also human prion diseases such as Creutzfeldt-Jakob disease, which seem to emerge spontaneously.

Chronic wasting disease was first identified on a Colorado deer farm in 1967 and has since been discovered across North America. Many of the free-range cases are in the mountain west of the United States, and Wisconsin and Pennsylvania have clusters.

Over the last three years, Minnesota’s prion research program has reviewed hundreds or even thousands of deer tissues for CWD. They have the equipment to look at hundreds of samples within 48 hours using a rapid diagnostic process called RT-QuIC, a technique that can detect prions in blood, feces, saliva and tissue — something Larsen said is thanks to nearly $2 million in state funding they received a few years ago. The USDA is still working to approve the TR-QUiC process, though Larsen said the agency will fully validate it in the next seven months.

Minnesota was the first to develop a field RT-QuIC test because of the funding, Larsen said.

Search efforts go beyond samples from deer, though as prions can persist for years in the environment. Larsen said the prions that cause diseases like mad cow or scrapie can persist in the environment for up to 16 years, and researchers in Colorado have found CWD prions can cause disease up to four years after being left in the environment.

Prions can also be detected in runoff from the soil into water, and there are currently surveyors taking water samples in Beltrami County to screen for prion runoff, Larsen said.

This year, Minnesota’s prion disease research program is seeking more funding from the state so it can continue honing its diagnostics and search for the disease.

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A part of an environment omnibus bill in the legislature includes more funding for ongoing surveillance efforts. But with just days to pass major spending bills in the Legislature and ongoing struggles over issues like public safety and K-12 education, it appeared uncertain if the program would get more funding this year.

Alex Derosier covers Minnesota breaking news and state government for Forum News Service.
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