Mad Cow Agent Found in Sheep Muscle
Sheep With Scrapie May Be Dangerous, Researchers Warn
May 24, 2004 -- Sheep with scrapie may be able to pass a kind of mad cow disease to humans, a new study shows.
Cattle get bovine spongiform encephalopathy -- BSE or mad cow disease -- from a dangerous prion (an abnormal form of normal cell protein) called PrPsc. When humans eat PrPsc in contaminated beef, it can give them the human version of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD). Scientists say vCJV comes from eating nerve tissue (such as that in the brain and spinal cord) from cattle infected with mad cow disease.
Sheep have their own form of the disease. It's called scrapie -- a fatal, degenerative disease affecting the central nervous system of sheep and goats.
Eating meat -- which is muscle -- of sheep with scrapie is not supposed to be dangerous to humans. But now researchers report finding PrPsc in sheep muscle. The findings, by Olivier Andréoletti of the National Veterinary School of Toulouse, France, and colleagues appear in the May 23 advance online edition of Nature Medicine.
"Dietary exposure to scrapie is currently considered nonhazardous to humans," Andréoletti and colleagues write. "However, the presence of PrPsc in muscles from sheep naturally infected with scrapie calls for a review of this question."
Making such a "review" more urgent is the recent finding that sheep can become infected with BSE as well as scrapie.
It's not clear exactly how much PrPsc-contaminated meat a sheep would have to eat to pose a danger to humans. Sheep have about 5,000 times less PrPsc in their muscles than they do in their brains. And the sheep in the Andréoletti team's study had to eat massive amounts of PrPsc to accumulate significant levels of the protein in their muscles.
"This is the first evidence for PrPsc in muscle from TSE-incubating animals of a species that enters the human food chain," Andréoletti and colleagues note.
SOURCE: Andréoletti, O. Nature Medicine, May 23, 2004; advance online edition.