EDMONTON - A new study has added to evidence that meat from deer infected with chronic wasting disease -- an infection similar to mad cow disease -- is safe for humans to eat.
"I think the inference is that humans probably are resistant to CWD," said Dr. Bruce Chesebro of the National Institute of Allergy and Infectious Diseases lab in Hamilton, Mont.
Chronic wasting disease affects animals such as deer and elk. It infects brain and spinal tissue and gradually causes the infected animals to waste away. It is always fatal.
The disease has spread to herds in Alberta and Saskatchewan from the United States, where it has been found in 11 states. Both provinces were trying hard to control it, but have given up on cull programs in affected areas.
Because of the disease's similarity to bovine spongiform encephalopathy, which is capable of infecting humans, hunters have long been advised to handle deer or elk carcasses from infected regions with care. But Chesebro's newly published study suggests there is little cause for concern.
His team attempted to infect a group of macaque monkeys, a species often used in lab tests because of its genetic similarity to humans. Researchers injected prions, the agent of infection, directly into the brains of one group of monkeys and fed prions to another group.
Nearly six years after they were exposed, none of the macaques has developed the disease. In contrast, spider monkeys injected and fed the prions developed the disease.
"Because humans are evolutionarily closer to macaques than spider monkeys, they may also be resistant to CWD," says the study.
Chesebro said there's no way to definitively know the disease can't infect humans, but he feels his results are suggestive.
"I don't want to say there's no risk, because there is some risk, but it's low."
His results correspond with the fact no hunters have ever been diagnosed with the disease, even though hundreds have probably been exposed in the last 30 years in the U.S. and Canada. Other research using human DNA transferred into mice also suggests that the chronic wasting disease prion doesn't transfer to people.
Still, Alberta is unlikely to change its advice to hunters, said Darcy Whiteside of the Sustainable Resources Department.
"We just want to be as safe as possible. I don't think we'll relax on that messaging."
The government advises caution in handling carcasses. It also offers a replacement tag to hunters who choose not to eat an animal they suspect has been infected.
But the province has given up on its controversial program to control the infection by killing off deer herds near the Saskatchewan boundary, where the disease has been found.
The incidence of the disease hasn't changed since it came to Alberta in 2005 and it remains small. Of 15,841 elk, moose and deer tested in 2008, seven tested positive.
Saskatchewan, which has also cancelled its deer cull program, has been finding an average of 45 positive deer in about 5,200 tested annually over the last three years.
No jurisdiction has ever been successful in ridding wildlife of chronic wasting disease once it appears.
