BSE in sheep poses huge health risk

By STEVE CONNOR

LONDON - Tens of thousands of people could die from eating lamb products contaminated with BSE if the cattle disease has transferred to sheep, says a scientific study.

There is no evidence that sheep have been infected with bovine spongiform encephalopathy (BSE), but scientists believe there is a strong possibility that it has happened.

Researchers from Imperial College London have calculated that if sheep were infected, as many as 150,000 people could die because of contaminated organs entering the human food chain.

That is three times higher than the "worst case" estimate for the maximum number of people that the same scientists believe could die from eating beef products contaminated with BSE.

(Only 113 people have so far developed the human disease, vCJD.)

The scientists also calculated that the risk from lamb could be reduced by 90 per cent if control measures were tightened so that all the internal organs of sheep were banned from human consumption.

Their warnings about the health threat from BSE in sheep rest on two main assumptions: that the disease has indeed passed from cattle to sheep and that over the years it has continued to spread from one sheep to another.

Their assessment, published yesterday in the journal Nature, says nothing about whether either of these assumptions is likely, but scientists believe both are highly plausible.

Professor Neil Ferguson, who led the Imperial College study, said: "In some ways I'd be surprised if BSE wasn't found in the sheep population."

It is known that contaminated feed caused the BSE epidemic in cattle, that the same feed was given to sheep in the 1980s - albeit in smaller amounts - and that sheep can develop BSE with symptoms similar to scrapie, a brain disorder of sheep that is harmless to humans.

Experiments have also shown that when the disease gets into sheep it behaves slightly differently to BSE in cattle.

It infects a wider range of tissues at an earlier stage in the animal's life, making BSE in sheep potentially more dangerous to consumers than an infection of cattle.

Also, BSE in sheep could behave like scrapie, where the infectious agent is transmitted relatively easily between animals. That is not the case with BSE in cattle where, because of bans on contaminated feed, the epidemic is now in sharp decline.

The ability of sheep BSE to transmit "horizontally" between animals would create a growing epidemic, as the infectious agent spread insidiously within the national flock of 20 million animals, its presence masked by the thousands of cases of scrapie reported each year.

The Department for the Environment, Food and Rural Affairs began a programme of sheep screening this month involving tests on 20,000 sheep at abattoirs and a further 3000 sheep that died before going to slaughter.

A spokesman said: "One of the problems is that you can screen lots of sheep and find the presence of scrapie, but right now we can't differentiate between the two.

"A lot of work is going on to try to validate a practical test which will do that."

In the absence of a quick and reliable test, scientists do not know whether sheep now have the disease and whether the risk is more than theoretical.

But the study demonstrates how serious the health risks to consumers would be if scientists did detect BSE in sheep. Ferguson and colleagues conclude that sheep BSE could now pose a greater threat to human health than the cattle disease.

"The current risk from sheep could be greater than that from cattle," said Ferguson, "due to the more intensive controls in place to protect human health from exposure to infected cattle, as compared with sheep."

- INDEPENDENT