SINCE “mad cow” disease (BSE) appeared in 1986, far closer surveillance has been put in place — both for cattle and for sheep, which can suffer from a closely related disease, scrapie.

An unusual form of this disease was detected in 2004 by the Veterinary Laboratories Agency as part of a survey of samples from abbatoirs and stock that died in the fields.

Atypical scrapie, as it is called, is neither traditional scrapie — which has been present in British flocks for 250 years — nor BSE.

One of its characteristics is that it appears in sheep whose genetic make-up makes them especially resistant to classic scrapie.

The unanswered question is whether atypical scrapie is a health hazard to humans. The chances are it has been around for a long time, but has been detected now because methods have become more sensitive.

Classic scrapie has never infected humans, so far as we know. So why worry that atypical scrapie might?

In the background is the awareness that ministers gave falsely reassuring advice about BSE when it emerged. They asserted, wrongly, that it could not transmit to humans. As we now know, in a few cases it can.

So scientists, Defra and the Food Standards Agency are bending over backwards not to make the same mistake again.

The trouble is that once the agency starts advising consumers to avoid products — mutton and sausage cases made from sheep intestines, in this instance — they raise the suspicion there is something to worry about.

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