The Truth About ...; Human BSE

PROVING THAT bovine spongiform encephalopathy (BSE) has crossed the species barrier from cows to human beings has been one of the most difficult scientific problems of late-20th-century medicine. Suspicions that BSE could pass into humans were voiced soon after the disease appeared in cattle in the mid-Eighties, but collecting the evidence that finally firmed up this speculation proved to be a far harder undertaking.

Creutzfeldt-Jakob disease (CJD) is the equivalent brain disease in humans and it has been known about since the early part of this century, long before BSE. Experts came to the conclusion early on that if BSE were able to pass into humans, then there might be a rise in the cases of so-called "sporadic" CJD. This classical form of CJD occurs in people who have no family history of the disease, and it strikes without any apparent reason - hence the name. The disease is also extremely rare, occurring at a rate of about one in a million people every year. Most doctors would never come across a case of sporadic CJD in their entire careers.

To make sure the country was able to detect any rise in the incidence of CJD, the government established a national CJD Surveillance Unit in 1990, based in Edinburgh. This unit is responsible for actively seeking out any information about unusual neurological disorders, as well as determining a diagnosis to see whether it may be CJD. The unit has since proved to be a world authority on this extremely rare and unusual disease.

Each suspect case of an unusual brain disorder is investigated with immense rigour, with the scientists asking relatives detailed questions about a patient's medical history, residence and lifestyle, such as his or her occupation and diet. They document the clinical symptoms of patients and analyse their brain material for signs of the neuropathology that distinguishes CJD from other brain diseases. Genetic tests are also done to see whether there may be something in a patient's DNA that can explain why they have developed the disease.

Sporadic CJD usually affects older people, with the average age of its onset being about 64. But in the second half of 1995 the unit began to investigate suspected cases of CJD affecting people under 30, which is extremely rare. (Up until then there had been only one confirmed case in a person aged under 30 - who died in 1980, just before the BSE epidemic took off.)

When Robert Will and James Ironside, the two principal investigators at the unit, looked in more detail at the cases in young people, they found that this form of CJD showed distinct differences from the classical characteristics of the sporadic disease. Under the microscope, the brain tissue of a new variant (nv) CJD victim displays distinctive, flowery structures of protein alongside the typical spongy holes seen in people with the sporadic form of the disease. Other features of the clinical symptoms suggested to Will and Ironside that what they had here was totally new to medical science.

When 10 cases of nvCJD came to light, the government made its famous announcement in May 1996 that the "most likely" explanation was that BSE had crossed the species barrier; but the hard proof of cause and effect was still lacking. It fell to the Neuropathogenesis Unit in Edinburgh to supply this evidence, in the form of a series of experiments on strains of genetically inbred mice.

When injected with brain material of an animal suffering from a particular kind of spongiform encephalopathy (such as sheep scrapie) each mouse strain exhibits a distinctive period of incubation before succumbing to the disease. The scientists, led by Moira Bruce, found that BSE and nvCJD had an identical "signature" that was quite distinct from those of sporadic CJD and scrapie. It was the closest science could get to proving that BSE could pass into humans to cause nvCJD, which could now justifiably be called the human form of BSE.

Steve Connor