NR APYT
AU Ferry,G.
TI Mad Cows and Loopy Lambs
QU Beagle 1998 Oct 30; 41
IA http://biomednet.com/hmsbeagle/41/people/pressbox.htm
AB A media panic erupted in Britain recently when it was suggested that mad cow disease has jumped to the sheep population. Some people have been accused of irresponsible behavior in raising the possibility in public, but what determines the difference between a scare and reasonable concern?
VT
Just for a moment, put yourself in the shoes of the poor government scientific adviser who has to pronounce on an issue of possible major importance for public health. Too reassuring, and one is guilty of complacency. Too alarmist, and one is a scaremonger. The month of September saw an outbreak of media panic in Britain over the possibility that bovine spongiform encephalopathy (BSE), or mad cow disease, might have spread to the nation's sheep population. This alarm was triggered by a quote from a member of the scientific committee advising the government about BSE and related diseases.
Are "Mad Cows" still a public health danger? What about sheep?
BSE, a degenerative brain disease in cattle, was first identified in the mid-1980s, and during 1991 and 1992, reported cases in Britain were running at more than 1,000 per week. In 1996, after assuring consumers that "British beef was safe to eat," the British government admitted there was almost certainly a link between BSE and a new form of the very rare Creutzfeldt-Jakob disease (CJD) in humans. A total of 29 people have died from new variant CJD, whose victims - some only teenagers - have been much younger than those of conventional or "sporadic" CJD.
The consequences for the British beef industry have been disastrous, with beef exports banned by the European Community, and the government paying out billions to farmers in compensation for slaughtered animals. Since the disease has an incubation period of several years, no one is prepared to risk a guess about the likely duration or extent of a human epidemic of new variant CJD. The epidemic in cattle has now declined to fewer than 100 suspected cases per week, but doubts persist about the effectiveness of controls introduced to prevent infective material from entering the food chain.
Consumption of beef products is still well below its former levels; only half of all British households still have beef on their shopping lists. Quite apart from its possible health implications, the idea that the whole sorry story could be repeated for lamb represents the worst possible nightmare for farmers and the men from the ministry.
Outside the lab, BSE has never been found in sheep.
So should those who like Welsh lamb nicely roasted with rosemary and garlic on a Sunday join in the panic? Let us get one fact straight from the beginning: no one has detected BSE in a single sheep that has not been deliberately infected with it in a scientific laboratory. Sheep do, however, suffer from a very similar disease known as scrapie. Scrapie has been endemic in the British flock for at least 200 years, with no apparent consequences for a British public with a keen taste for lamb chops and leg of mutton. Despite the brouhaha over BSE, scrapie was not made a notifiable disease until 1993; since then, affected sheep and goats must be slaughtered and the carcasses destroyed. As of 1996, sheep brains, spinal cords, and spleens are not allowed to be used for food. Farmers have received compensation for slaughtered sheep and goats only since earlier this year.
Until 1988, when the practice was banned, farmers fed sheep the same feed, made of ground-up ruminant carcasses, that is thought to have started the BSE epidemic in cattle. Two years ago, scientists established that sheep can develop BSE if given it deliberately in their feed; this news caused an almost identical media flurry, one that seems to have been largely forgotten since. So at least theoretically, it is possible that some sheep have BSE. If they do, the consequences could be very serious. BSE in sheep behaves like scrapie - it affects more organs than it does in cows, effectively contaminating the whole carcass. Another worry is that BSE could be transmitted like scrapie, which passes from sheep to sheep in the field and therefore becomes endemic. According to the official view, BSE does not do this in cows, although it can pass from a cow to her calf.
A news report in Nature started the latest media panic.
The government's Spongiform Encephalopathy Advisory Committee (SEAC) turned its attention to the problem of sheep, BSE and scrapie at its meeting on July 30. They decided to set up a subcommittee to plan a program of research. The subcommittee chair is Jeffrey Almond, professor of virology at the University of Reading. A news report on this in Nature on September 3, including an interview with Almond, brought the issue into the public eye once more, although a surprisingly sluggish national press took almost a week to pick it up.
Was Almond being a scaremonger when he told Nature that "We could be facing a potential national emergency"? The problem for a public trying to evaluate the risk is an almost total lack of relevant information. At the moment, the only reliable way to tell whether a sick sheep has BSE or scrapie is to inoculate carefully selected mice with the sheep's brain tissue, then wait two years to see which pattern of disease develops. So far, this test has been done for a total of nine sheep. All turned out to have scrapie. Almond argued (with some justification - there are around 20 million sheep in Britain) that this result was completely inadequate as a guide to the likely presence of BSE in the British flock. "'Absence of evidence' is often confused with 'evidence of absence,'" he said. Nearly all newspaper and TV reports following the Nature article repeated this remark with relish.
The test currently used to distinguish BSE from scrapie takes years.
Almond's object was not to panic the population, but to publicize the need for more research. This view was endorsed by his SEAC colleague, John Collinge of the Prion Disease Group at Imperial College School of Medicine. For more than two years, Collinge has been working on a test that might be able to distinguish scrapie from BSE in hours, rather than years, by comparing the profiles of the sugars attached to the prion protein that accumulates in diseased brains. It could potentially allow tests on much larger numbers of animals. Although the Ministry of Agriculture, Fisheries, and Food (MAFF) has committed almost a quarter of its £12.7 million BSE research budget to spongiform encephalopathies in sheep, Collinge has so far failed to obtain its backing to develop his test. Objectors argue that the test is not sufficiently accurate to be useful, and stress the catastrophic consequences of a false positive result. Inevitably, there is media suspicion that MAFF is burying its head in the sand.
Consumer groups fear a repeat of the government foot-dragging that characterized every step of the BSE drama, with equally disastrous results. The same article in Nature publicized a letter sent to Tessa Jowell, the minister of state for public health, by Sheila McKechnie, head of the UK Consumers' Association. McKechnie opened up another front by suggesting the government advise parents not to feed lamb to children who had not been previously exposed to the risk of BSE. When challenged on this point on national radio, SEAC members dismissed the suggestion, arguing (somewhat off McKechnie's point) that young children were no more susceptible to BSE than anyone else.
Urgently needed: a quick test to show wether BSE has jumped to sheep.
But what exactly should SEAC recommend? Almond, who initially found himself cast in the role of scaremonger-in-chief, put the dilemma in a nutshell in an interview on BBC Radio. "[Politicians] would have to live with the possibility that, if they went down the road of stopping the consumption of sheep meat, 20 million animals would be destroyed, a whole industry collapsing, and the consequent cost to the nation of that. To do nothing would be inappropriate, while to ban lamb would be ridiculous." SEAC argues that the first priority should be more research, to develop a quick and accurate diagnostic test for BSE. If such a test reveals that BSE has indeed jumped to sheep, that will be the time to consider introducing further controls.
The panic, such as it was, has been largely a media phenomenon. Farming publications have reported with some relief that the scare seems to have had little effect on lamb sales. Perhaps, after the food scares of the past decade - BSE, salmonella, E. coli - British consumers are becoming skeptical about the idea that things they like eating are likely to kill them. If so, that is bad news for Richard Lacey, former professor of microbiology at the University of Leeds and scourge of government complacency. The sheep meat scare came just in time to prepare the ground for his new book, serialized in the Daily Mail. Its title? Poison on a Plate.
Georgina Ferry is a scientific journalist based in Oxford, England.
Caleb Brown is an illustrator and biologist living in Montana. By day he drives a delivery van, and by night he draws pictures with his computer.
SP englisch