Dissecting chronic wasting disease

August 8, 2002 Milwaukee Journal Sentinel by MARK JOHNSON 
Denver -- The barriers preventing chronic wasting disease from spreading to cows and humans remain formidable, more than 400 hunters, public health officials and scientists were told Wednesday.

Cattle living in pens near deer and elk infected with chronic wasting disease have shown no evidence of the disease after five years, said University of Wyoming researcher Elizabeth S. Williams, an early pioneer in the study of the disease. Nor, she told participants in a national symposium on the deadly deer disease, have cattle on the range in Wyoming and Colorado picked up a bovine version of chronic wasting disease.

At the molecular level, a study found that chronic wasting disease faces less of a barrier in jumping to sheep and a much greater barrier in jumping to humans or cows, said Gregory Raymond, of the National Institutes of Health's Rocky Mountain Laboratories. While the research emboldened some conference participants to conclude that chances of a hunter contracting chronic wasting disease were remote, others were less encouraged.

"I am not as confident as some of the speakers," said Patrick Bosque, a neurologist at Denver Health and assistant professor in the University of Colorado Department of Neurology. "I think a few people overemphasized the lack of evidence of transmission of (chronic wasting disease)." So far no evidence has emerged of chronic wasting disease infecting humans. But Bosque stressed that relatively few Americans have been exposed to venison infected with the disease, especially when compared with the number of people in Britain exposed to contaminated beef during the recent "mad cow" outbreak. An estimated 50 million British residents were exposed to contaminated beef; so far about 124 have come down with the human version of the disease, called variant Creutzfeldt-Jakob.

Also, work by Bosque and other researchers has found that prions, the deadly infectious agent blamed for chronic wasting disease, "mad cow" and Creutzfeldt-Jakob, could accumulate in the skeletal tissue of artificially infected mice. This finding could be significant if studies now under way show that infected cows and deer also accumulate prions in muscle tissue, which humans eat.

Up to now, experts have said prions accumulate in the brain, lymph nodes and spinal cord, and they have advised hunters to avoid cutting into those areas when butchering deer.

The U.S. Centers for Disease Control and Prevention has investigated cases of a few unusually young victims of Creutzfeldt-Jakob disease -- under the age of 30 -- who regularly consumed venison. But investigators "found no strong evidence for a causal link" between chronic wasting disease and any of these young Creutzfeldt-Jakob victims, said Ermias Belay of the CDC.

Belay also mentioned the cases of three men who took part in wild game feasts in northern Wisconsin and subsequently died of rare brain diseases -- two of them from Creutzfeldt-Jakob. The feasts featured deer and elk meat, including some from states with chronic wasting disease. The cases were first reported in the Journal Sentinel last month.

Reluctance to do autopsies

"These cases are being investigated as we speak in collaboration with the Wisconsin Department of Health," Belay said.

Public health officials in Colorado and Wyoming, both states with chronic wasting disease, told the symposium that they have been tracking Creutzfeldt-Jakob cases in their states, but so far have found no evidence of unusually high rates.

However, they have run into a snag that sheds light on just how deep the fear runs surrounding prion diseases. Although every case must be reported, both states have had difficulty finding coroners, pathologists or medical examiners willing to conduct autopsies of Creutzfeldt-Jakob victims.

"It's fear, concern, unknowns," explained John Pape, an epidemiologist for the Colorado Department of Public Health and Environment.

Autopsies of Creutzfeldt-Jakob victims often employ special precautions, Pape said. They use specially designed coffin boxes in which only the victim's head is exposed, and everything else is draped in plastic. Emergency rooms are set up to avoid any contamination of surfaces.

He expected relatives of some dead people to be opposed to the idea of an autopsy; he did not expect such resistance to come from those who conduct autopsies.

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