Inquiry rejects outright belief that disease is 'sheep scrapie in cattle'

A British problem

One of the most intriguing aspects of the Phillips inquiry is that it throws open the question about the exact origin of BSE and why Britain should have been so badly affected.

One of the most intriguing aspects of the Phillips inquiry is that it throws open the question about the exact origin of BSE and why Britain should have been so badly affected.

Lord Phillips said that the investigation had rejected the view of the scientific establishment, which for years had proposed that the disease was, in effect, sheep scrapie in cattle.

Scrapie is one of the best-known transmissible spongiform encephalopathies (TSEs), having been recognised as a problem in sheep for at least 200 years. Early on in the BSE epidemic, government scientists had assumed that scrapie-infected carcasses of sheep had been rendered into cattle feed, enabling the infectious agent to cross the species barrier from sheep to cow.

"This was reassuring because scrapie does not infect humans. We do not believe that BSE is scrapie in cattle. BSE is a new, and more potent disease than scrapie," Lord Phillips said yesterday at the launch of his mammoth 16-volume report.

The Phillips inquiry accepts that the BSE epidemic was caused by the amplification of infected material by the rendering of affected cattle carcasses into cattle feed. But this does not explain how BSE got into cattle in the first place.

"Nobody knows why the first cow or cows got BSE, but we believe that from this single source infection spread widely in the British herd before anyone realised that a new disease had come into existence," he said.

Scientists are still mystified about the precise nature of the infectious agent that causes BSE and its human form, vCJD. The current view is that infectious proteins, or "prions", cause the disease and that they can come about through spontaneous mutations.

A spontaneous mutation could have occurred as long ago as the Seventies, causing BSE prions to enter the food chain in the rendering process. Whatever the agent is, it can survive temperatures that would normally kill the typical microbes and viruses that cause all other infectious diseases known to medical science.

For 30 years scientists have tried, and failed, to find a virus or virus-like agent that could be responsible for scrapie, which led to the hypothesis that it was caused by prion proteins alone.

The "protein only" theory was pioneered by Stanley Prusiner, of the University of California, who was eventually awarded a Nobel prize for his work. He believes the defective prion protein is able to "infect" healthy proteins in the brain by causing a conformational change in their normal three-dimensional structure. This change causes the proteins to accumulate to a point that they interfere with the normal brain functions, causing microscopic pores in the "spongy brain".

There is now wide support for the hypothesis. The strongest argument in its favour is that the prion protein appears able to cause the disease without needing the genetic material (such as DNA) that every other pathogenic microbe, from viruses to fungi, needs to cause disease.

But some scientists, notably from the Neuropathogenesis Unit in Edinburgh, where research into sheep scrapie began in the Sixties, find the hypothesis hard to reconcile with their work showing genetic information of some kind seems to be necessary for causing the many strains of scrapie.

Understanding the exact cause of vCJD is more than of mere academic interest. Isolating the infectious agent that is behind the disease would lead to better drugs aimed at blocking its modus operandi. It could also help explain the long and variable periods of incubation between infection and the onset of symptoms.

Isolating the cause of vCJD could also help scientists understand what needs to be done to avoid passing on the infection, for instance in blood transfusions. And, most helpfully, it could lead to a test for answering the biggest question of all: how many healthy people are currently incubating vCJD?