Science scrambles to study CWD

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Scientists study whether humans can get wasting disease

7/1/02

DENVER (AP) - Federal researchers are trying to determine whether a fatal brain disease in deer and elk is a danger to humans who eat venison.

Experts say there's no evidence the infection can spread to livestock or humans, but the possibility can't be ruled out.

"That's what everybody is trying to find out," said Dr. Pierluigi Gambetti, head of the National Prion Disease Pathology Surveillance Center, based at Case Western Reserve University in Cleveland.

Chronic wasting disease eats holes in an animal's brain, and the animal becomes emaciated. It is always fatal to deer and elk.

Richard Race, a research scientist with the National Institutes of Health's Rocky Mountain Laboratory in Hamilton, Mont., said primate research is the most direct way to learn whether people are susceptible.

"It's the species that's most closely related from an evolutionary point of view to people. You cannot inoculate humans on purpose, so the next best thing is some kind of a non-human primate," he said.

Race said the research was likely to be disputed, both by scientists who might fault the methods and advocates who condemn experiments on animals.

"If word gets out that it's actually being done, you get all the animal protest groups and people like that bugging you all the time," he said. "One thing about it if we do it here (at the Hamilton lab) is that security is really tight."

Gambetti's group plans studies of genetically manipulated mice to see if they can be infected with chronic wasting disease.

"We don't know whether it can be transmitted to humans, and if it is transmitted, what it's going to look like," said Gambetti.

Most scientists believe chronic wasting disease, mad cow disease and Creutzfeldt-Jakob disease, which affects humans, are caused by a mutant protein called a prion.

The researchers believe a strong barrier prevents prions from one species from infecting another. But 131 Europeans contracted a variant of Ceutzfeldt-Jakob by eating cattle suffering from mad cow disease.

Some mice experiments already under way have not detected human susceptibility, said Patrick Bosque, a Denver neurologist who conducted some of the research in the San Francisco laboratory of Nobel laureate Stanley Prusiner.

Bosque said those mice have been manipulated to contain a human gene that produces human protein. The protein was inoculated with chronic wasting disease.

After more than 600 days, the protein has not changed to the deadly mutant prion form.

However, a control experiement indicated the mouse model might be flawed. Mad cow disease prions were injected directly into the brains another group of mice, and they showed no susceptibility to the disease, even though humans are known to be vulnerable to the disease.

Race is the lead researcher on another mice experiment that has raised new questions.

Mice that were injected with hamster prions showed no outward or microscopic sign of the disease. But when brain matter from those mice was injected into another set of mice and hamsters, they became sick from mutant prions and died.

That raised concern that if chronic wasting disease infected other species, the first generation of the infected animals might not get sick.

"It used to be thought the hamster (prion disease) didn't go into mice. There was a species barrier," said Anne Raines, a scientist at Rocky Mountain Laboratory. "And now we have some of those mice going down in a short amount of time, 100 days or so."

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On the Net:

National Prion Disease Pathology Surveillance Center: http://www.cjdsurveillance.com/

National Institutes of Health: http://www.nih.gov/
 
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