THE BSE RISK: Britain holds breath on CJD epidemic

The nation may know by the end of this year whether it faces an epidemic of people suffering from Creutzfeldt Jakob Disease (CJD) triggered by eating BSE-infected beef in the 1980s.

Government scientists are urgently re-examining their original risk assessments of the dangers posed by eating BSE-infected beef products. They want to see what the chances are that the 10 CJD cases which alerted them to a possible link with BSE were the tip of a slowly surfacing iceberg - or a statistical blip.

"We are on tenterhooks about the scenario that might emerge," said one member of SEAC, the independent expert committee, yesterday. "But we think it should become clearer in the next six-to-12 months. If we don't see too many cases then it could be that there won't be an epidemic."

To guide them, the scientists on SEAC and at the Government's own laboratories have three existing models for the transmission of "spongiform encephalopathies" - of which BSE is one type. One is scrapie, the form it takes in sheep; another is feline spongiform encephalopathy (FSE), which affects cats; and the third is kuru, caused by cannibalism in humans, but which is effectively indistinguishable from CJD.

Kuru has a median incubation period of about 12 years, and the 10 CJD cases appeared in the past two years. This, say the scientists, implies that the victims were exposed to the disease agent in about 1983-84, when the BSE epidemic was just beginning. If these 10 people represent the typical proportion of the population who will contract CJD, many thousands of people could succumb in the next five years, having eaten infected material between 1983 and 1989.

However, the case of FSE may be a better guide. That first appeared in cats in 1989, almost certainly from eating infected cattle remains in food. But though it must have had an incubation period, and the number of cases of BSE did not peak for another three years, the number of cats diagnosed as having FSE has not increased radically, but has remained fairly steady.

"It could be that the reason for that is that we don't recycle cat offal to feed to cats. That was done with cows - and the BSE epidemic followed. The thing to remember is, we don't recycle human remains," said one scientist yesterday, weighing up the potential for an epidemic. That would imply that the new, BSE-induced CJD required a high dose and only affected certain susceptible individuals - meaning that the number of cases will remain comparatively low.

Significantly, Rob Will, head of the CJD Surveillance Unit, which spotted the new trend in CJD cases in February, told the Independent yesterday: "We do not have a large number of suspect CJD cases in the pipeline."

It could be that BSE is not easily passed on to humans. People have eaten sheep infected with scrapie since the 18th century, but the incidence of CJD is not related to the incidence of scrapie: countries such as New Zealand, where scrapie is unknown, still record cases of CJD.

Accurate projections of the number of cases of CJD that may arise in a population exposed to BSE-infected meat, are further hampered by the lack of diagnostic tests for CJD before symptoms appear.