What causes BSE?
BSE in the UK comes from using animal feed containing contaminated meat and bone meal as a protein source. Health officials suspect that cattle were contaminated by either scrapie-affected sheep or cattle. Scrapie is a fatal, degenerative disease affecting the central nervous system of sheep and goats.
What is the likelihood of catching BSE?
The information keeps changing. In the latest scare, in August this year, Professor John Collinge said that new research showed that animals thought to be healthy and incapable of acquiring BSE can, in theory, pass the disease on. Experiments on mice and hamsters have suggested that similar diseases could jump between species more easily than previously thought. His findings have sparked renewed concern that humans not displaying variant CJD symptoms but incubating the condition may infect others during medical or dental procedures. However, Professor Smith, acting head of the government's BSE advisory comittee SEAC, today said that the risk of becoming infected now from beef products was very small and "attributable almost certainly to exposure" when the levels of contaminated product was at its zenith in the food chain.
How many people have died?
In total, at least 70 people have died of CJD. Prof Smith said today the final numbers it may yet kill as likely to be from between a few hundred to several thousand people. He said early estimates of an epidemic were "farily implausible".
Has there been a recent outbreak of CJD?
Health officials are investigating a cluster of five cases around Queniborough, just north of Leicester. These included three victims dying within a few of months in 1998, a fourth who died in May 2000 and another patient, still alive, who is thought to be suffering from the disease.
Are people still being infected?
This is what perplexes scientists. Until today's findings, the prevailing scientific opinion was that humans were almost certainly not still being infected. The government's expensive programme of slaughtering all cattle aged over 30 months and - temporarily - banning the sale of beef on the bone minimised public exposure to BSE-infected meat and was thought to have caused the disease to almost die out in Britain's beef herds. But the latest research published by the National Academy of Sciences will cause a rethink.
What was last week's polio BSE scare about?
An oral polio vaccine, Medeva, was recalled last week over fears of CJD. The vaccine, which had been used in up to a third of inoculations for children and travellers, contained tiny traces of a feoetal calf growth serum from potentially BSE-contaminated animals. However, the risks of infection from the vaccine were said to be "incalcuably small". The Department of Health said the firm, also Medeva, had misled them on assurances the vaccine met new BSE safety guidelines.
What did the research revealed in August involve?
Prof Collinge's team found that mice injected with hamster scrapie, a BSE-like disease, carried high levels of infectivity while living into old age without outward symptoms. But when material from the brains of these mice was injected into other mice, it eventually killed them. The worry is that the process created a new strain - or strains - of a more virulent disease.
Do the latest findings contradict recent information?
They do seem to go against research released earlier in August when scientists said CJD could ultimately claim 136,000 lives, a much smaller number than previous estimates. At one point there seemed to be no limit to the numbers potentially at risk. A European committee thought that a single animal with BSE could put up to 500,000 people at risk.
Why were the numbers revised?
In a report in the journal Nature, scientists from Oxford concluded that any sick animal that entered the food chain was liable to infect no more than two individuals, and only 40% of the population was genetically susceptible, leaving the incubation period as the other key factor. If the incubation period was less than 20 years, there could be as few as 63 cases. If the incubation period stretched to almost lifetime length - 60 years - then there were likely to be 136,000. What matters over the next few years is the annual rate of increases. "If the average annual incidence of CJD over the next three years is fewer than 15 cases, then the maximum total number of cases would fall to 20,000," they wrote.
How did the Conservative government deal with the BSE crisis?
Many people think that the issue could have been addressed far earlier. BSE was identified in November 1986 but ministers were not informed about the disease until June 1987. Although measures were subsequently put in place to keep meat most likely to be infected away from the dinner tables, it was not until 1996 that the government admitted that there might be a serious risk to human health. The Labour government launched an official inquiry into the way the crisis was handled. This was the inquiry that reported back today.
Useful links
Nature
BSE cases abroad
Ministry of Agriculture: the BSE inquiry
The BSE inquiry
Department of Health's CJD figures
US department of agriculture