Two separate scientific experiments have shown the most convincing evidence yet that food infected with "mad cow disease", or BSE, causes the fatal human illness of "new variant" Creutzfeldt-Jakob disease (v-CJD).
The new work is described as "compelling" by professors John Pattison, chairman of the Government's advisory committee Seac, and Jeffrey Almond, a virologist who also sits on Seac.
On hearing the news, the lawyer acting for the families of people who have died of v-CJD reiterated his call for a judicial inquiry into how the infection occurred.
"The Government announced the possibility of a link in March 1996," said David Body, of the solicitors Irwin Mitchell.
"The other week, an inquiry was announced within 48 hours after a train crash where six people died. So far, it's taken 18 months to do nothing about v-CJD."
His call was echoed by Dave and Dot Churchill, whose 19-year-old son was the first victim of v-CJD. They met MEPs in Britain on a fact-finding mission about BSE yesterday.
So far, 20 Britons have died of v-CJD. But hundreds, or even thousands of people, may have eaten a deadly dose.
However, neither Professor Pattison nor Professor Almond, nor John Collinge, another Seac member who carried out one of the experiments, feels that the new work can help predict the future size of any epidemic of v-CJD.
"Guessing numbers would be foolish at this stage," said Professor Collinge, of St Mary's Medical School. Scientists also feel it is too early to predict the incubation time of the disease in humans.
The first of the two experiments released yesterday, both published later this week in the science journal Nature, studied the brains of mice which had been infected with tissue from people who died from v-CJD. It compared them with those of mice infected with BSE, and with other mice injected with "sporadic" CJD, identified in the 1920s, which causes about 50 deaths annually in the UK.
The first results of the studies by Dr Moira Bruce at the Neuropathogenesis Unit in Edinburgh have taken two years. They show that the same agent causes BSE and v-CJD.
A separate paper, by Professor Collinge, reached the same conclusion by a different route, using two groups of mice with human genes. One group was injected with tissues from cattle with BSE, and another from a person who died of v-CJD. Collinge's group found molecular characteristics peculiar to BSE in the v-CJD mice.
Yesterday, Professor Collinge said "the level of evidence that has now been produced to support the hypothesis [that BSE causes v-CJD] is overwhelming". He thought that alternative suggestions - such as a common infectious agent which affected both cows and humans separately - were "not really defensible any more".
But his work with transgenic mice implies that the cases of v-CJD now appearing are just the first, possibly with an incubation time since infection of 10 years. In cattle, it was five years.
However, genetic variation could mean more people will fall ill up to 30 years from now.Reuse content