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Canada’s leading pathologist on mad cow disease shook up the deer hunting world this year when she delivered to an international gathering of prion disease experts an alarming study with implications for human exposure to chronic wasting disease (CWD).

By feeding moderate amounts of diseased venison to macaques monkeys over a period of years, Dr. Stefanie Czub found what no one wanted her to find: CWD can be transmitted to non-human primates who are genetically close to humans.

In an interview with the Star Tribune last week, Czub (pronounced Shoob) said she quietly revealed her study findings to the U.S. Centers for Disease Control and Prevention (CDC) before announcing the preliminary results in May at the Prion 2017 conference in Edinburgh, Scotland.

In turn, just before this year’s deer and elk hunting seasons, America’s top public health agency “strongly’’ recommended that hunters who harvest deer and elk in CWD-infected zones have the animals tested before eating the meat.

Czub takes it a step further. Her advice to North American whitetail hunters, including the 500,000 people who will hunt deer this year in Minnesota, is to test your kill regardless of where you harvest it.

“This is a disease with a long, extended incubation period,’’ said Czub, a professor, veterinarian and researcher at the University of Calgary who also works closely with the Canadian Food Inspection Agency. “It’s not your average food poisoning.’’

To Minnesota State Public Health veterinarian Joni Scheftel, the most compelling aspect of Czub’s research is that two test monkeys became infected with CWD prions after eating muscle meat from infected whitetails that appeared healthy at the time of their death. Prions are abnormal proteins that cause fatal nervous system disease.

“It certainly got all of our attention in public health,’’ Scheftel said of Czub’s research project, now in its ninth year.

Taking precautions

The news of Czub’s $7.9 million CWD study is reverberating. Two weeks ago, the owner of a venerable Wisconsin meat company cited the research when interviewed by the Green Bay Press Gazette about the company’s difficult decision to stop making venison sausage. The CDC recommends that venison from deer harvested in known CWD areas not be mixed with other deer during commercial processing.

Silver Creek Specialty Meats co-owner Tom Kramlich told the newspaper the family-owned firm no longer feels confident that it isn’t taking in venison from CWD areas that have grown to include 19 Wisconsin counties.

“I never thought there was a safety issue, but this Canadian study makes a person sit up and take notice,’’ Kramlich said.

Ryan Maddox, an epidemiologist with the CDC in Atlanta, said the agency is eager for the completion of Czub’s research, which could happen by the end of the year. But the agency “hasn’t heard too much in the way of negatives’’ for intensifying its guidance to hunters and families that eat venison. He said the CDC involved wildlife agencies in forming the advice.

A year ago, CDC was telling hunters that there is no strong evidence of CWD transmission to humans but that people should avoid eating meat from deer and elk that look sick or that test positive for CWD.

That message has changed and is now amplified with a reference to Czub’s research on the CDC website: “In areas where CWD is known to be present, CDC recommends that hunters strongly consider having those animals tested before eating the meat.’’

Minnesota watching

Maddox said Minnesota is one of several states where CWD has been identified for enhanced human prion disease surveillance. Public health officials want to know if human prion diseases could be occurring at a higher rate in people who are at increased risk for contact with potentially CWD-infected deer or elk meat, he said.

“Because of the long time it takes before any symptoms of disease might appear, these studies will need to be conducted for many years before they will determine what the risk, if any, of CWD is to people,’’ Maddox said.

Czub said CWD prions showed up in the two monkeys who ate muscle meat after five and six years of feeding.

Scheftel said CWD guidance from the Minnesota Department of Health hasn’t changed. The agency “does not recommend that people consume meat from a prion-infected animal, or from any animal that appears ill.’’ Hunters also should request that their animals be processed without including meat from other deer and avoid eating brain, spinal cord, eyes, spleen, tonsils or lymph nodes from deer.

Before last year’s deer hunting season, Minnesota had no known cases of CWD in its wild deer herd. That changed when routine DNR testing of whitetails harvested near Lanesboro and Preston uncovered 11 CWD-infected deer. Subsequently, CWD was found in captive deer on two Minnesota deer farms.

As a result, the DNR on opening weekend of the firearms deer season this year will conduct mandatory CWD testing in 21 deer permit areas centered on Fillmore County in the southeast, Crow Wing County and Meeker County. Hunters will be notified if their deer tests positive for CWD.

Mandatory CWD testing will continue throughout the season in the CWD management zone inside Fillmore County, at DNR expense. But the agency also recognizes that some hunters outside CWD-surveillance areas may want to test their game. The DNR recently placed a video on the CWD pages of its website to teach hunters how to extract lymph nodes from a deer’s neck.

The DNR recommends that the lymph nodes be submitted for testing to the University of Minnesota Veterinary Diagnostic Lab, where fees start at $45. But Dr. Jerry Torasson, director of the lab, said he wants hunters to know it costs only $17 for CWD testing at Colorado State University’s Veterinary Diagnostic Lab.