Although the research cannot show whether 12 recent cases of a new variant of the brain disorder, Creutzfeldt-Jakob Disease (CJD), were caused by eating BSE-infected food, it offers the first detailed analysis of the number of infected cattle that were eaten.
Described as "valuable and helpful" by the Government yesterday, the study also shows that between 1985 and 1989 - when the most infectious tissues, such as the brain and spinal cord, were still used in food - 446,000 BSE-infected cows were eaten. That represents about 3 per cent of the total of roughly 3 million cows killed every year.
In March, the Government said exposure to BSE-infected food could have been the cause of the new cases of CJD. The European Union subsequently banned British exports of beef and its by-products.
The study, which was carried out by a team at the University of Oxford, also shows that the Government's policy of culling all cattle aged over the age of 30 months will have little effect on the length of the BSE epidemic. The disease will not die out until 2001, no matter what action is taken, the scientists say, because it is now sustained by "maternal transmission" from cow to calf. Previously, BSE-infected feed was the main route of transmission.
Jeffrey Almond of SEAC, the independent advisory committee on BSE and CJD, said last night: "The big shock in this paper is the proportion of [infected] animals eaten before the 1989 ban. "But the important - and still unknown - figure is what proportion of those were in the late stages of BSE incubation."
The analysis is published today in the science journal, Nature.
"We have been able to estimate the magnitude of the potential problem, but there's still the issue of whether infected animals are infectious to people," said Christl Donnelly, one of the report's authors, yesterday.
"But with only 12 cases of the new CJD, it's impossible to predict what might happen."
Professor Almond admitted: "There's not much that we can do for any people who might be incubating CJD. We can't diagnose it, and we can't cure it."
There was wide agreement last night that the culling policy - which is now underway across the country - was a shotgun approach to a problem which needed more specific targeting.
"We would have to cull more than a million animals to make much difference," said Dr Donnelly. "Any less than that and you are reducing less than half of the cases. For example, culling 150,000 cattle would reduce cases by 34 per cent."
A better method, argued the report's authors, would be to focus on cattle herds which had already experienced high incidences of BSE, as these would be more likely to include infected calves.
Professor Almond agreed: "Culling is an expensive way of dealing with the problem and has little added impact on it."
The Ministry of Agriculture, Fisheries and Food said that the comparison of culling strategies offered in the analysis was "of particular interest". However, its spokesman would not comment on the public health implications of the consumption of BSE-infected cows.
The Meat and Livestock Commission welcomed the analysis. "We will certainly look at this data, and if it looks like the cull is not needed then that is great news for farmers," said Phil Saunders.
"We have said all along that we expect BSE to fade out by the end of the century. But at the end of the day, we have to look at consumer confidence.
"We must be sure that people understand that British beef is safe. We have to be careful before we shake up the whole system again."Reuse content