Current measures to prevent meat from animals infected with mad cow disease from entering the human food chain are effective, scientists said on Thursday.

Researchers at the CEA research centre in France have estimated that a person would have to eat 5 grams (0.2 ounce) of tainted tissue from an animal showing clear signs of the disease to be at risk of developing Creutzfeldt-Jakob disease (vCJD).

“It is almost impossible now with the measures that have been taken to reach these doses,” Dr Jean-Philippe Deslys told AMN Health.

Since 1989 the brain and spinal cord of the central nervous system of cattle have been banned for human consumption. Animals are also tested for signs of mad cow disease, or bovine spongiform encephalopathy (BSE).

“The combination of the two measures is very efficient,” said Deslys.

If an infected animal that was just below the test limit was shown to be negative for BSE, 1.5 kilograms (3.3 lb) of its infected tissue would have to be consumed to pose a health risk, according to the research.

The scientists, whose findings are reported online by The Lancet medical journal, estimated the amount of infected tissue people would have to eat by giving adult primates 5 grams of ground brain tissue from a BSE infected cow.

One animal developed a disease similar to vCJD five years after it was infected but the other animal remained healthy.

Using their results and the findings from other studies they calculated the amount of exposure to BSE that would be dangerous to humans.

“Our results provide reassurance that BSE screening procedures combined with central nervous system removal are effective measures to protect the human food chain,” Deslys said in the study.

But vCJD experts said there were fundamental problems comparing likely human exposure based on primate studies.

“Multiple oral exposure events over a period of years seems likely in the UK, and vCJD occurs predominantly in young adults, raising the possibilities of age-related susceptibility or exposure,” Professor James Ironside, of the University of Edinburgh, said in a commentary on the research.

Because of the long incubation period, which Deslys and his colleagues estimate could be up to 50 years, it has been difficult to predict how many cases of vCJD there will be.

Up to Nov. 1 last year, 146 people had died from definitive or probable vCJD in Britain, according to the Department of Health.

SOURCE: Lancet, online January 27, 2005.