The infectious proteins that cause brain-wasting disease have been found in the leg muscles of infected deer, a laboratory experiment shows.

Scientists say there is no evidence people have caught the disease from infected deer. But the new findings, in Friday's issue of the journal Science, suggest hunters could potentially be exposed from sick animals.

Chronic wasting disease affects ranched elk and wild deer in Saskatchewan and Alberta, according to the Canadian Food Inspection Agency. It is also found in deer and elk across the U.S. West and Midwest.

Chronic wasting disease has been found in elk and deer in North America. (CP file photo)
Chronic wasting disease has been found in elk and deer in North America. (CP file photo)

Like BSE or mad cow disease, chronic wasting disease is a "transmissible spongiform encephalopathy." In such diseases, infectious proteins called prions infect the brain and spinal cord.

The brain gradually becomes spongy and the infected animal or person eventually dies.

Prion researchers don't yet know if prions that cause chronic wasting disease can infect people the same way BSE prions can lead to variant Creutzfeldt-Jakob disease in humans.

If so, eating, handling and preparing carcasses could potentially expose people to prions.

"It's certainly unsettling," Dr. Neil Cashman, a prion scientist in Toronto, told the Canadian Press.

"We are concerned here in Canada with the possibility that hunters and native people are being exposed to CWD prions in what are called country foods, so we've got our eyes open. We're alert to the possibility that there could be a transmission."

Unanswered questions

U.S. scientists found mice bred to be susceptible to CWD prions came down with the disease when given extracts of muscle meat from infected deer.

When the mice were injected with extracts from the brain of infected deer, the lab animals were infected faster. The finding suggests nervous system tissue carries more prions than deer muscle.

Mice injected with tissue from healthy deer were unaffected, report Glenn Telling of the University of Kentucky and his colleagues.

People who hunt deer in areas where chronic wasting disease has been found are already told to throw out the brain and spinal cord, and to not eat animals that clearly have the disease.

Scientists don't know the extent of prion contamination in deer muscle, or if prions spread among deer that aren't sick.