출처 : ScienceDaily  Aug. 3, 2009
 http://www.sciencedaily.com/releases/2009/07/090730111152.htm

ScienceDaily (Aug. 3, 2009) — Data from an ongoing multi-year study suggest that people who consume deer and elk with chronic wasting disease (CWD) may be protected from infection by an inability of the CWD infectious agent to spread to people. The results to date show that 14 cynomolgus macaques exposed orally or intracerebrally to CWD remain healthy and symptom free after more than six years of observation, though the direct relevance to people is not definitive and remains under study.

Cynomolgus macaques often are used as research models of human disease because they are very close genetically to humans and are susceptible to several forms of human brain-damaging disease. Thus, it was decided to see whether exposure to CWD could induce disease in the macaques. The study appears online in the journal Emerging Infectious Diseases.

CWD is a type of brain-damaging disease known as a transmissible spongiform encephalopathy (TSE) or prion disease. CWD primarily affects deer, elk, and moose. Other TSE diseases include mad cow disease, or bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep, and sporadic Creutzfeldt-Jakob disease (CJD) in humans. Humans are not susceptible to sheep scrapie, but BSE appears to have infected about 200 people, primarily in Europe in the 1990s. Those findings provided the rationale for the present CWD-macaque study, which began in 2003.

“We plan to continue this study for at least several more years because, although the risk to macaques so far appears to be low, we know that these diseases can take more than 10 years to develop,” says Bruce Chesebro, M.D., chief of the Laboratory of Persistent Viral Diseases at Rocky Mountain Laboratories (RML) in Hamilton, Mont. RML is part of the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH). The RML group is leading the study with collaborators from the Colorado Division of Wildlife; State University of New York Downstate Medical Center; New York State Institute for Basic Research in Developmental Disabilities; American Red Cross; and the University of Wyoming.

The findings by the RML group support published field studies done by others in regions of Colorado and Wyoming where CWD is endemic. Between 1979 and 2001, there were no significant increases in human TSE diseases despite the likelihood that hunters in those areas were exposed to CWD through contact with infected animal tissue and contaminated hunting tools such as knives and saws. Extensive laboratory data also supports a human species barrier against CWD.

Notably, the RML study also included identical testing in squirrel monkeys, which are genetically less similar to humans than macaques. Of 15 squirrel monkeys exposed orally to CWD, two displayed disease symptoms 69 months after infection. Of 13 squirrel monkeys exposed intracerebrally to CWD, 11 displayed symptoms between 33 and 53 months after infection. In symptomatic animals, the presence of the CWD agent was confirmed in brain, spleen and lymph nodes.

The results in squirrel monkeys were not surprising because a study elsewhere in two squirrel monkeys yielded similar results. The study by the RML group was different, however, in that it tested oral exposure to CWD and also studied eight CWD samples from different areas of the country. The results in squirrel monkeys confirmed that disease progression in that species appears consistent with disease progression in deer and elk, where severe weight loss is nearly always present.

“The fact that the squirrel monkeys, like the deer and elk, suffered severe weight loss suggests that chronic wasting disease might affect a common region of the brain in different species,” notes Dr. Chesebro.

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Journal reference:

1. Race B et al. Susceptibilities of nonhuman primates to chronic wasting disease. Emerging Infectious Diseases, DOI: 10.3201/eid1509.090253

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U.S. study suggests deer infected with chronic wasting disease safe to eat

Provided by: Canadian Press
Written by: Bob Weber, THE CANADIAN PRESS
Aug. 3, 2009

출처 : C-Health - Aug 03 8:23 AM


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. THE ASSOCIATED PRESS/Ed Andrieski

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.