Evidence of rogue proteins associated with brain-wasting diseases has been found in the leg muscles of sheep, the first such finding in animals that enter the human food chain.
Scientists said the discovery involving the sheep disease scrapie nevertheless does not seem to pose a significant threat to people.
The proteins, called prions, have been found in the muscles of infected humans and rodents but not previously in the muscle tissues of animals whose meat is commonly eaten by people. Also linked to prions are mad cow disease and chronic wasting disease in deer and elk.
A researcher who studied the scrapie-infected sheep said the possibility that the prions would infect people appears very unlikely because of extremely small amounts of the proteins measured in the muscle.
Better exams of sheep, goats needed
Jacques Grassi of the Pharmacology and Immunology Service of the Department of Medical Research, CEA-Saclay, France, said the finding suggests that a more complete examination of muscles is needed from sheep or goats infected with scrapie strains and whose muscle meat could enter the human food chain.
Grassi, a co-author of a paper appearing Sunday in the online edition of the journal Nature Medicine, cautioned against extending results of the research to mad cow disease.
That disease, formally known as bovine spongiform encephalopathy, also is caused by prions but has a much lower rate of infection for tissues beyond the brain and spinal cord than does scrapie.
Variant Creutzfeldt-Jakob Disease is the human form of mad cow disease associated with eating beef from infected cattle. It has been blamed for 143 deaths in Britain and 10 elsewhere. No Americans are known to have contracted the disease in this country, although one case of disease has been reported in a cow.
Scrapie no threat to humans?
Robert B. Petersen, a neurological specialist at Case Western Reserve University in Cleveland, noted that scrapie has existed for 300 years and does not seem to pose a significant threat to human health.
“However, the endemic occurrence of scrapie creates the potential for transmission to other animals that may be a threat to human health,” said Petersen, who was not part of the research team. Like any infectious agent, he said, it is possible the scrapie prion could mutate.
William D. Hueston of the University of Minnesota said that while the report is the first to show prions in muscle tissue of an animal in the human food chain, it is not a major cause for alarm.
Scrapie tends to infect more tissues in an animal than mad cow disease does, he said. While this suggests the prion that causes illness in cattle eventually might be found in muscle tissue, it probably would be in very small amounts.
The research was supported by the French ministry of research, the European Union and the French region of Midi-Pyrenees.