Study cites new CWD fear

Afflicted deer have infectious agents in leg-muscle tissue

Todd Hartman, Rocky Mountain News

Published January 27, 2006 at midnight

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A new study has found that deer infected with chronic wasting disease have infectious agents present in their muscle tissue - a discovery that reverses long-held thinking and reinforces calls for hunters to test their kill and avoid eating infected deer.

The new information, published Thursday in the journal Science, found that leg muscles from infected deer contain infectious prions, the agents believed to lead to the fatal neurological disease in deer and elk.

The results repeal established assumptions that the infectious prions concentrate only in the brain, spinal cord, lymph nodes and other central nervous system tissues, and that those were the parts of the animal that hunters should avoid.

The Colorado Division of Wildlife's Web site, for example, advises hunters that muscle tissue from infected deer is safe for consumption.

"Research to date . . . indicates that the prions do not accumulate in muscle tissue of deer and elk, thus hunters are advised to bone out their meat and consume only muscle tissue of deer and elk killed in infected units."

But the study, which involved collaboration of scientists in Colorado, Kentucky, Florida and Zurich, Switzerland, found otherwise.

The researchers injected material taken from the leg muscle of infected mule deer into genetically altered mice. The mice went on to develop neurological deterioration associated with chronic wasting disease, sparking authors of the paper to include cautionary statements for people.

"These results show that . . . muscle, which is likely to be consumed by humans, is a significant source of prion infectivity," the study said. "Humans consuming or handling meat from CWD-infected deer are therefore at risk to prion exposure."

Though there is still no known case of a human contracting chronic wasting disease from eating an infected deer or elk, many scientists believe people still should take precautions.

In large part, that's because a related disease in cattle, called bovine spongiform encephalophaty, or BSE - known popularly as mad cow disease - has been tied to the deaths of about 150 people who've acquired the human version of the illness after eating infected meat.

Patrick Bosque, a neurologist at Denver Health who studies prion illnesses, is among those who suggest caution.

"It may be that humans are completely resistant to this disease," Bosque said. "But we don't know that."

Bosque said it might be that so few humans have contracted a version of CWD from eating infected deer or elk that cases haven't been noticeable yet.

"The bottom line, if the rate of transmission from deer to humans is . . . low, it might not be evident (in humans) based on the ways we have for looking at it," Bosque said.

Colorado researchers who participated in the study, Mike Miller at the state Division of Wildlife and Edward A. Hoover at Colorado State University, said the findings reinforce suggestions that people avoid eating deer that appear sick.

"Have your animal tested, and if your animal is positive, you can't assume that . . . any part of the animal is free from infectious CWD," Hoover said.

But both scientists emphasized that the highest levels of the infectious agents are still to be found in parts of the central nervous system, including the brain.

In fact, part of the study found that mice injected with infectious material from the brain developed the disease faster than when injected with diseased muscle tissue.

Miller said previous methods of looking for infectious prions didn't turn up any presence of the agents in muscle tissue, but the new technique used in the latest study did.

"We know now that, at least in the end stage of disease, there is some amount of infectivity in the muscle tissue, which is something we didn't know before," he said.

hartmant@RockyMountainNews.com or 303-892-5048

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