Is the incidence of BSE actually falling or is it as high as ever because farmers are concealing sick animals? Has the risk of an epidemic of the human form of BSE receded or is there worse to come?
There was vigorous disagreement among scientists yesterday during a discussion on the risks and lessons from BSE during the British Association Festival of Science, under way at Cardiff University.
"We still predict the disease [BSE] will be at an extremely low level by 2001," said Prof Roy Anderson of the University of Oxford, a member of the UK government's Spongiform Encephalopathy Advisory Committee.
However, the controversial University of Leeds scientist, Prof Richard Lacey, claimed that the incidence was not falling.
He said there was enormous pressure on farmers not to report cases as the UK government had cut compensation levels for sick animals.
He argued that there should be regular BSE testing at beef production plants to establish by random sampling the level of BSE in the UK herd. This was not now being done.
Britain has a very different BSE level and control regime from Ireland, and the disease continues to cause it problems. UK beef exports are still banned, whereas both Irish and Northern Irish exports were cleared by the EU.
The disease has always been much more common in the UK herd, compensation for sick animals is below market value and there have been over 20 UK cases of human BSE, known as new variant CJD (nvCJD).
BSE in Ireland is a tiny fraction of that in Britain. Despite the size of the national herd, generous compensation is paid to farmers and there have been no Irish nvCJD cases. Ireland has a more rigorous slaughter policy than the UK.
Prof Lacey said it was impossible to make a prediction about future nvCJD incidence on the basis of the cases so far. His analysis did not preclude a large epidemic.
He said the incubation period for the disease was about nine years, so it would be some five years before reliable estimates could be made. In the meantime, scientists would "have to learn better how to say `I don't know"' when asked for definitive data.
He did not believe that random BSE sampling in the beef factories, as currently happens in the Republic, would be valuable because too large a sample would be required to gain any real knowledge of the underlying incidence.
A colleague on the advisory committee, Prof John Collinge, of Imperial College, London, disagreed, taking a similar position to that of Prof Anderson. He described new, very accurate and inexpensive testing methods which could be applied. He agreed with predictions that BSE was in decline and would be virtually gone by 2001.
He said random testing would confirm this. It would also provide answers to the theoretical possibility that some diseased animals might still be reaching the human food chain by harbouring BSE while remaining symptomless.
The scientists agreed that there was under-reporting of the disease. "Most diseases are underreported. Undoubtedly, there is under-reporting going on now," said Prof Anderson.
Prof Lacey said it was a shame that BSE was not a notifiable disease requiring compulsory reporting.
