Scientist in new CJD warning

Published on Sunday 1 December 2002 00:00

HUMANS still face the risk of contracting the human form of mad cow disease from eating the muscle and flesh of cattle and sheep, a Nobel Prize-winning scientist claimed last night.

Stanley Prusiner, the expert who first discovered that infected material could cause brain diseases, offered a stark warning that eating meat could still pose a serious health risk.

He claimed that regular meat from cattle and sheep may harbour deadly levels of prions that cause Creutzfeldt-Jakob Disease.

Scientists had believed that only the brains and spinal columns of cows and sheep contained dangerous levels of prions.

The alert reawakens concerns about the dangers of BSE and variant CJD, after health officials had hoped the threat from the diseases was decreasing.

Prusiner revealed that experiments at the University of California, in San Francisco, had shown that scrapie-infected mice have unexpectedly high concentrations of deadly prions in their muscles.

"These are just mouse models, but they raise the obvious worry that cows and sheep could be similarly affected," said the scientist, who won the 1997 Nobel Prize for medicine, for his discovery that degenerative brain conditions like vCJD are caused by prions.

The research indicates that prions may be present in cuts of lamb and beef largely consisting of muscle, rather than the brain and spinal tissue previously blamed for carrying the disease from animals into humans.

"The levels we found were a hundredfold less than those found in brains, but were still significant," Prusiner added.

"In particular, we found that the hind legs of mice had high numbers of prions. It remains to be seen whether that is mirrored in the hind legs of cattle or sheep."

Prusiner’s team has developed a new test for detecting prions in samples - one that is 10,000 times more sensitive than systems currently in use in Europe and America.

He said: "Previous attempts to quantify BSE and scrapie prions in milk or non-neural tissue, such as muscle, may have underestimated infectious levels by as much as a factor of 10,000, raising the possibility that prions could be present in these products in sufficient quantities to pose risk to humans.

"The high sensitivity of this new test may profoundly alter our view of the epidemiology of prion diseases."