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CWD carriers among us?

August 8, 2002 Rocky Mountain News (Denver, CO) by Todd Hartman and Lou Kilzer
A National Institutes of Health scientist called Wednesday for further research to determine if deer, elk, cattle - or even humans - might be silent carriers of chronic wasting disease, harboring the illness until it can infect others.

Richard Race, a leading-edge researcher on CWD and similar diseases, told 450 fellow scientists, government officials and wildlife advocates that "One might wonder if there are people who are (carriers)."

Race's experiments on mice and hamsters show that some maladies in the family of diseases known as transmissible spongiform encephalopathies (TSEs) can lie undetected in one set of test animals, then spring to life with fatal consequences when transmitted to others.

"If these people are subclinical carriers, do they represent a threat to other people?" Race asked. Already, human cases of a related brain disease - Creutzfeldt-Jakob Disease, or CJD - have been transmitted during surgical processes involving contaminated body tissues and medical instruments.

While there are no known cases of CWD - a degenerative neurological disease of deer and elk - infecting humans, the tenor of debate on the issue has changed.

A year ago, some biologists scoffed at the notion that CWD was any risk to humans. Wednesday, a parade of experts ventured to the podium to discuss their research into what has become a major area of study.

"The (possibility of) transmissibility of CWD to humans remains unclear," said Gregory Raymond, a colleague of Race's at the NIH's Rocky Mountain Laboratories in Montana.

Race discussed his research into a molecular species barrier that may - or may not - stop CWD from infecting humans, cattle or other species.

University of Wyoming veterinarian Beth Williams updated the audience on another critical issue: Could roaming deer and elk infected with CWD pass it to cattle, therefore jeopardizing the beef supply?

Ongoing experiments show three cattle with CWD injected into their brains have become infected. But other cattle exposed to the disease orally and simply by sharing pasture space with infected deer and elk over the past five years have not become sick.

"These experiments are not complete, and we know the incubation period (for the disease) can be a long time," Williams said. "But so far I'd have to say the news is good as far as CWD transmissibility to cattle."

But Race said Williams' study, and another like it in Iowa, need to be extended. His suggestion: Once the experiment is complete, take brain matter from surviving cattle and inject it back into uninfected cattle and mule deer to see if the next generation of animals contracts CWD.

This is similar to the kind of experiments Race had overseen involving passing the disease between hamsters and mice, and goes to the question of whether the disease can be carried without causing disease in its current host.

Race believes the infectious agents may be able to evolve and adapt as they pass through generations of species, then at some point cause active disease in a species other than that of its original host.

Amir Hamir, a scientist working at a USDA laboratory in Iowa, said he would welcome talking with Race about the experiment with cattle and deer. "That can be done," he said. "But it is very, very expensive" because of the cost of caring for large mammals over years.

Medical experts at the conference were also discussing a recently discovered case in Wisconsin, in which three hunters in their 50s and 60s who often engaged in so-called "venison feasts" all died in the 1990s of neurological diseases, two of them from CJD.

The cases have only now have come to the attention of the Centers for Disease Control. The CDC's interest was fueled by the February discovery by Wisconsin wildlife officials of CWD in the state's white-tailed deer.

"We are investigating as we speak," said Ermias Belay, prion disease expert with the CDC.

In an interview, he said his agency wants to examine the deceased men's brain tissue and confirm diagnoses made when they died. Investigators are also gathering reams of information from family members. Still, Belay said, it may be hard to be definitive about the cases.

"You can speculate, but there is no hard data to tell you if they had exposure to (CWD-contaminated venison) in Wisconsin," he said. "One of these (men) died in 1993. If he was exposed in Wisconsin, you have to look back 10 to 20 years" at the meat he consumed. The meat - if meat even had anything to do with it - could have come from many other places, Belay said.

The greatest concern was expressed by Western Slope veterinarian Dick Steele. He fretted that CWD is a human health threat that isn't being taken seriously enough by wildlife officials.

He said if the disease does adapt to cross into humans, and proves as infectious as CWD is among elk and deer, there would be "some pretty serious consequences." He also noted that, compared with British exposure to mad cow disease - where more than 120 people have died out of a population 60 million - exposure to CWD is far lower, perhaps too low for any human cases to be detected yet.

"Human exposure to CWD has been so limited that statistically we are unlikely to have seen one single case at this time," Steele wrote in a summary of his presentation. "To say there is no evidence that CWD cannot transmit to people is quite premature."

But Gary Wolfe, of a Montana-based information-sharing network called CWD Alliance, said fear-mongering over the disease is unnecessarily threatening hunting economies and cultural traditions. He cited a Wisconsin poll of hunters showing 37 percent of respondents were "seriously considering" not hunting this fall.

Risks are everywhere in life, Wolfe said. He cited everything that can go wrong on a hunting trip - car accidents, firearm and knife injuries, falling off a horse, even a heart attack in the high country. Common sense measures, such as wearing gloves when dressing a carcass, go a long way, he said.

"We could find out at some point (CWD) is transmissible to humans," Wolfe said. "But keep the risks in perspective."

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