CJD and the doomsday scenario

五月 8, 1998

'Too secret...too late'

The BSE panic began in March 1996 when ministers announced the discovery of ten deaths among young people from an "unusual" form of the rare Creutzfeldt-Jakob Disease, and that they probably got the disease from eating beef. Some scientists warned that the next decade could see thousands of deaths among people who had eaten beef infected with BSE, aka mad cow disease.

BSE is a degenerative disease of the nervous system that spread through the country's cattle in the 1980s. Ministers claimed that the route of infection had been largely closed by 1990. Nonetheless beef sales across Europe plummeted, slaughterhouses emptied, and the European Union banned British beef exports worldwide.

For scientists, the crisis began in September 1995, when James Ironside, a neuropathologist at the Western General Hospital in Edinburgh examined the spongy brain of a teenage CJD victim. He already knew it was unusual. Cases in people so young were extraordinarily rare: the previous 25 years had seen just one such victim under 30 years old in Britain. What Ironside saw down the microscope made it, for the moment, unique. The pattern of degenerating brain tissue was like nothing he had seen before: great blotches of protein, rather than thin fibres.

Several similar cases soon followed. It dawned on Ironside and his boss, Robert Will, at the hospital's CJD monitoring unit that the "doomsday scenario" the unit had been set up six years previously to watch for might be happening. With no common risk factors among its victims other than eating beef, the most likely explanation of this new form of CJD was that it was a human form of "mad-cow disease". And if BSE could pass to humans in beef, most of Britain's population was potentially at risk.

BSE and CJD, along with the sheep disease scrapie, are examples of a range of diseases found in many animals and known as spongiform encephalopathies. The infective agent is believed to be a rogue protein known as a prion, a biological novelty whose existence was for many years disputed by scientists. The diseases can pass from one species to another, but when and how remains unclear.

But since the mid-1980s it has seemed possible that BSE might pass from sheep to cattle, although not all scientists accept sheep scrapie is the source of BSE. Meat and bone meal from sheep carcasses, some infected with scrapie, have been fed to cattle since the 1920s by a process that used a solvent to extract the tallow. But in the early 1980s, solvent extraction was replaced by heat treatment to separate the tallow. This change appears to have increased the infectivity of scrapie. And from the mid-1980s, vets began to come across cases of "mad cows".

The animals typically became edgy and uncoordinated, then aggressive, then lame - and died. Their brains were riddled with holes, like a sponge. Scientists named the disease Bovine Spongiform Encephalopathy and, according to their evidence to the inquiry, MAFF scientists concluded by December 1987 that "ruminant-derived meat and bone meal was the only viable hypothesis for the cause of BSE." In April 1988, the government asked Richard Southwood to head a working group to investigate the disease. One of the group's recommendations was that the hypothesis that sheep were the origin of BSE should be tested. Southwood told the inquiry that had still not been done.

Within weeks of Southwood's appointment, ministers banned sheep and cattle remains from cattle feed and instituted the rule that sick cattle should be destroyed. But by then animals with symptoms of BSE were numbered in thousands. In November 1989, the government banned from human consumption certain organs from cattle that were known to harbour the disease, such as the brain and spinal cord. Even so, there was enough unease that ministers agreed in 1990 to set up a permanent body, the Spongiform Encephalopathy Advisory Committee, to monitor the situation. It also launched a programme to "evaluate changes in patterns" in the occurrence of CJD in humans "which might be attributed to BSE". It was that research programme, based in Edinburgh, that saw the first cases of "new variant" CJD in late 1995.

CJD is no new disease. Worldwide, it affects about one person in a million each year. Its incubation period before it reveals symptoms is many years. Virtually all victims are old (average age 63). Until now.

The ten victims revealed in March 1996 were all between 18 and 41 years old. And their symptoms were subtly different. Unlike traditional sufferers, who became forgetful and developed odd behaviour, these younger victims became chronically depressed and anxious - like cattle with mad-cow disease. But what convinced Will and Ironside they were looking at a new form of CJD was the state of the dissected brains of its victims. In all spongiform diseases "fibrils", or threads, of protein form in the brain. In these new victims the fibrils had turned into large clumps and there were many more of them.

One SEAC member, virologist Jeffrey Almond of the University of Reading, says "the possibility that BSE might transmit to humans has been acknowledged among scientists since the disease was first recognised in British cattle". But it had always been played down. One government scientist likened the chance of BSE infecting humans as like that of being struck by lightning. Well, lightning struck. In the immediate aftermath of the March 1996 announcement, ministers and members of SEAC argued there was no public health purpose in a slaughter of British cattle. Their case hung on the assumption that, after the tighter controls proposed by SEAC, the "leakage" of BSE into the human food chain was sealed. But this was something that European vets and public health officials were less inclined to believe. They argued that, until the disease had been substantially eliminated from British cattle, the risk to humans was too great. They sided with Southwood, who said in March 1996 that "a slaughter of all animals born before early 1991" was probably necessary to bring the number of new cases to a handful a month and restore public confidence.

The epidemic among cattle has been massive. The British Medical Journal reported in late 1995 that 1.8 million cows were probably incubating BSE and would enter the human food chain. They would be eaten by over 30 million beef-eaters. So far, 24 people have died of the new-variant CJD. Scientists have been encouraged by the slow increase in numbers, but warn it is too soon to be sure there will be no epidemic. The length of the incubation period in humans was emphasised by the recent death of a woman who had not eaten meat for over ten years. She is presumed to have contracted the disease in the mid-1980s, long before the period of peak exposure. The potential for a human epidemic is real.

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