New mad cow woes
4 to 6 percent of mule deer in parts of Colorado and Wyoming have chronic
wasting disease, a relative of mad cow.
The TSE in question is called chronic wasting disease, and it's been found for decades in two western states. Less than 1 percent of Rocky Mountain elk, and 4 percent to 6 percent of mule deer and white-tailed deer in southeast Wyoming and northeast and north-central Colorado have chronic wasting disease, says Elizabeth Williams, a professor of veterinary science at the University of Wyoming and a pathologist at the state veterinary laboratory. The disease is also present in captive herds in five or six states, she adds.
Williams, who has studied the problem for two decades, says the numbers has been very stable, especially for the past four years in Wyoming, where a large sample produces solid statistics. "It's a slow, chronic disease, and we wouldn't expect wild swings of prevalence."
The disease is diagnosed from slides of brain and lymph tissue made with sensitive immune techniques, she says. In fact, the detections are so sensitive that the "percentages of affected animals we find are not readily comparable to data on other spongiform encephalopathies," she says. Tests of tonsils may detect disease just 42 days after inoculation, extremely early for a TSE.
Williams says the TSE could move either from mother to offspring, or horizontally from one animal to another. "Given the amount of disease in the area, and to fit the epidemiology, it has to be transmitted horizontally."
She says the probable mechanism is fecal-oral transmission. "Somehow the agent gets into the feces, and an animal comes along and consumes forage" contaminated with feces. Alternatively, the prion could be present in saliva. An upcoming research project will address transmission issues.
Nobody is known to have been sickened directly by chronic wasting disease, and there is no evidence that cattle have been infected. However, as biologist Tom Pringle points out, these is some evidence that this prion could infect people more or less as readily as the BSE prion does.
Translated: Chronic wasting disease could be as dangerous as mad cow.
What's being done to protect the U.S. food supply?
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