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Scientists say CWD unlikely to jump to humans, but other experts aren't so sure

August 10, 2002 Associated Press
Most scientists at a national chronic wasting disease symposium downplayed the chance that the fatal nervous system disease in deer could cross the species barrier to humans.

Ermias Belay of the Centers for Disease Control said investigations of unusually young Cruetzfeldt-Jakob disease patients found no strong evidence of a causal link between CWD and the Cruetzfeldt-Jakob human variant of abnormal prion protein disease. And Gregory Raymond of the National Institutes of Health cited experiments in which he said that humans, cattle, sheep and rodents resisted the abnormal CWD protein prion. "These results demonstrate a barrier at the molecular level that could limit the transmissibility of CWD" from the deer family, Raymond said.

But Dr. Dick Steele, a veterinarian and member of the Western Colorado Sportsmen's Council, raised the issue of a public health danger if the disease is transmitted.

Steele said that CWD was not just a remote individual health risk for a hunter deciding whether to eat deer meat.

"This is a human health threat with some serious consequences if it crosses the species barrier. It is transmitted by animal-to-animal contact. This is by ingestion or inhalation of saliva, feces or possibly urine. This is how many human diseases are transmitted such as the common cold and salmonella," Steele said.

"If it crosses to one human being, it could potentially instigate an epidemic. The really threatening aspect is we would not know it existed until it had spread among the population for 10 or more years when the first person exhibited clinical symptoms. During that time, a person could expose hundreds of people."

Hunters field dressing deer sometimes work as a group, which is not a controlled situation, he said. And perhaps brain tissue could cause contamination when antlers are removed.

One theory is that CWD has already jumped a species barrier by originating in sheep scrapie and becoming CWD in deer. Steele asked why it could not jump a species barrier again.

"We need CWD stopped," he said. "I am a proponent of depopulation."

Other speakers at the symposium were less pessimistic about whether the disease could reach humans, however.

Shu Chen, a scientist with Case Western University and the National Prion Disease Pathology Surveillance Center at the university, said the purpose of the center is to collect, characterize and store all cases of suspected and proven prion disease in the United States.

As of last March 31, he said, 787 cases have been examined and 576 had a prion disease, but no case of variant Cruetzfeldt-Jakob disease was detected.

"We have found that prion in CWD is similar to one type of CJD," he said. "More testing and data are needed to determine whether there is any risk of transmission of CWD to humans."

The Centers for Disease Control is investigating, in collaboration with the Wisconsin Department of Health and Family Services, a case revealed by the Milwaukee Journal Sentinel in which three men who participated in venison feasts in Wisconsin later died.

Richard Race, of the National Institutes of Health, found that transmissible spongiform agents could persist in a resistant species for years and not result in clinical disease.

"New and varied strains can arise," he warned. "Disease in a new host may not mimic the exact characteristics in the original. We do not know if what we got is worse than what we had."

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