The facts you need to know

Fears of an epidemic of brain disease may prove well-founded Photograph by TONY BUCKINGHAM

The link to humans

The Government accepted last week that there is a possible link between 10 fatal cases of Creutzfeldt-Jakob Disease (CJD) and mad cow disease, or BSE. It had previously stressed that there was "no evidence" of a link. The scientific community has always been divided on the likelihood of a link. There is still no definitive proof. But BSE is given as the most likely cause of the CJD contracted by the 10 recent victims.

What we are eating

Bovine offal, which is known to carry BSE in infected animals, was banned for human consumption in November 1989. But the first cases of mad cow disease emerged in 1985. During this period, says one microbiologist, the entire UK population would have been exposed to BSE. He suggested it was too late now for anyone to stop eating beef - unless you were born since then. However, some experts say the effect is cumulative: the more BSE-infected meat you eat, the greater the risk.

The people at risk

Little can be said about BSE with certainty; it is a game of chances. You are most likely to be at risk if you eat bovine offal, but there is some risk in eating even a prime cut of beef. You are safer with imported beef. Most vegetarians have not escaped because gelatine, made from cow off-cuts, is used in so many food products. Despite a series of measures introduced since 1988, an unknown number of infected cows have entered the human food chain, as many as 1.8 million according to one microbiologist.

How it is transmitted

BSE is known to be spread among cattle by eating infected bovine feed. A ban on this kind of feed was imposed in 1988. BSE typically has an incubation period of five years. Scientists are divided on whether it is spread among cattle in other ways. The most likely additional cause is passing from mother cow to calf. An organic farmer, Mark Purdey, has carried out tests that, he says, show BSE is spread by organo-phosphorous used to eradicate warble-fly in cattle dip. His claim has increasingly been taken seriously.

What happens now

The recent CJD cases are "different" because they have hit both teenagers and dairy farmers. It represents a new strain, and seems to be sparked by BSE. Since CJD has a long incubation period in humans, from a minimum of around 10 years, there could be many more cases over the next few years and decades. How many is anyone's guess. It will probably run into at least the hundreds, some predictions put it in the millions.

Mark Watts