Scientists fear that BSE may have infected sheep

Click to follow
The Independent Online

Government scientists have found evidence to suggest that BSE may have infected sheep – something that was until now considered to be only a theoretical possibility.

The preliminary findings of an experiment designed to test for bovine spongiform encephalopathy (BSE) in sheep could, if confirmed, fatally undermine an industry already suffering from the biggest crisis in its history.

The Food Standards Agency issued a guarded statement yesterday about the experiment, designed to test for BSE in the early 1990s when the cattle epidemic was at its height. The agency said the results "could be compatible with BSE having been in sheep at that time" although the findings are neither complete nor clear.

Scientists have told the agency that although the experiment has more than a year to run, there are early signs that some of the sheep diagnosed in the early 1990s with scrapie – a degenerative brain disease similar to BSE but harmless to humans – may actually have been suffering from BSE, caught as a result of eating contaminated meat and bonemeal made from rendered cattle carcasses.

If sheep did have BSE 10 years ago, the disease could since then have become endemic in the nation's breeding flock of 20 million animals, and BSE-infected lamb could have entered the human food chain.

Confirmation of the results would automatically lead to a tightening up of safety measures designed to protect consumers, with a more extensive ban on sheep offal and a possible prohibition on mutton from older animals.

The experiment, carried out by government scientists at the Institute for Animal Health in Compton, Berkshire, involved "pooling" the brains of about 3,000 sheep thought to be infected with scrapie and injecting the material into a panel of five genetically distinct strains of mice. Each strain has a unique incubation period, with one type of mouse, called R3, dying within a year if it is injected with BSE. Another strain, C57, dies 100 days later.

It is understood that these two strains have died after an incubation period that strongly indicates – but does not prove – that the "scrapie" was in fact BSE. Neither the Institute for Animal Health nor the Food Standards Agency would answer questions on the precise nature of the results.

A similar experiment involving the injection of human brain material into the R3 and C57 strains was used to prove that the variant form of Creutzfeldt-Jakob disease (vCJD) was derived from BSE.

The FSA referred to its prepared statement, which says: "The research itself, which involves long incubation periods in mice, will not be fully completed for another year. But if BSE was present in the samples it should be clear by late autumn." The agency also suggested another possibility: that the sheep brains were unwittingly contaminated with BSE by scientists using the same instruments to extract the brains of both scrapie-infected sheep and cattle with BSE. "Our experts advise us that it is not yet possible to draw conclusions from this research since the work is not yet complete and the possibility that there may have been contamination of the samples with BSE-infected cow brains needs further investigation," it said.

"It is also expected that the issue of possible contamination will be resolved by [autumn]. If the data suggest that BSE was present in sheep at that time and contamination is an unlikely explanation, a further issue will remain to be resolved: what significance would BSE presence in the early 1990s have for today?"

One fear is that BSE in sheep may act more like scrapie, which infects more parts of the carcass and is easily transmitted from mothers to offspring. If so, there is a risk that BSE could have become endemic in the national flock.