NR ACBR
AU Butler,D.
TI Doubts over ability to monitor risks of BSE spread to sheep
QU Nature 1998 Sep 3; 395(6697): 6-7
PT news
VT
DECLAN BUTLER
Has 'mad cow disease' - BSE - infected sheep in the United Kingdom? Scientific advisers to the UK government and the European Commission are calling for research to assess the risks to be stepped up.
Scientists studying bovine spongiform encephalopathy agree on one thing: that there is a very real risk that BSE may have passed into flocks of sheep and goats in the United Kingdom and elsewhere.
UK sheep were fed BSE-contaminated meat and bone meal until the July 1988 feed ban, and limited experiments have shown that sheep fed infected cattle brain can succumb to BSE.
It remains unknown whether BSE has entered the UK sheep population, but is going undetected because its symptoms are indistinguishable from those of scrapie, a spongiform encephalopathy endemic in UK flocks, but which does not seem to transmit to humans.
However, if BSE has really passed into the sheep population, the consequences for human health could be extremely serious. "We could be facing a potential national emergency," says one member of the UK government's Spongiform Encephalopathy Advisory Committee (SEAC). Given that BSE seems capable of infecting humans via the oral route, SEAC judges that infected sheep tissues could likewise "pose a potential risk to human health if eaten".
SEAC, which reports to the agriculture ministry and the health department, confirmed last month that the total number of UK cases of new-variant CJD, the human version of BSE, is 27. Epidemiologists say it is still too soon to reach any conclusions about the scale of any epidemic.
Not enough research is being done to assess how significant the danger of sheep BSE might be, according to many scientists. Unease persists within SEAC which is to set up a sub-committee to draft proposals for a large expansion of research. The European Commission's independent Scientific Steering Committee is also scheduled to recommend more research at the European level
This year the UK Ministry of Agriculture, Fisheries and Food (MAFF) is spending £2.8 million (US$4.6 million) of its £12.7 million BSE research budget on sheep spongiform encephalopathies, and the Biotechnology and Biological Sciences Research Council has budgeted £3 million over the next three years.
In July 1996, SEAC recommended more research to establish levels of scrapie in sheep and to assess the risks of BSE. An abattoir survey of the incidence of scrapie in sheep brains, suggested by the committee, began in August 1997, while the MAFF imported more than 1,000 scrapie-free sheep from New Zealand at the beginning of this year for pathogenesis and transmission research.
Uncertainty Sir John Pattison, SEAC's chairman, says the new subcommittee "will be the best way of developing specific recommendations". A MAFF spokesperson declined to comment on research needs before the subcommittee has delivered its recommendations, but said MAFF would follow SEAC's advice.
SEAC members admit that, as a result of the current insufficient effort to detect BSE in the sheep population, decisions on public health measures are based on uncertainty rather than science. Epidemiological data on scrapie-like cases is so poor throughout Europe that it is impossible to even tell whether the incidence has changed over the past decade.
Scientists are particularly concerned about the speed and scale of experiments to detect BSE strains in sheep. Conventional strain typing studies to distinguish scrapie from BSE are burdensome and take years. So far, results from only nine UK sheep isolates have been published.
Jack Cunningham, until recently Britain's agriculture minister, has publicly interpreted these results as reassuring: "So far all the samples studied have revealed scrapie and not BSE. Scrapie is a disease endemic in the UK and France for over 200 years and which is to our knowledge, while analogous to BSE, harmless to man."
Many scientists are more cautious. "Having found zero out of nine, what confidence can we attach to the statement 'BSE is not present in sheep'?" asks Jeffrey Almond, a virologist and professor of microbiology at the University of Reading, who is a member of SEAC. "The answer is very little; 'absence of evidence' is often confused with 'evidence of absence'."
He points out that, to have a hope of detecting BSE levels as low as 0.1 per cent of supposed scrapie cases, for example - a level that would have significant consequences for public health - thousands of scrapie cases would need to be screened (see box).
Until the risk of BSE in sheep is better assessed, scientific advisers are left contemplating an unknown risk. If BSE had entered the sheep population in the 1980s it may still be present. SEAC considers that, whereas cattle are a dead-end host for BSE, there is evidence that in sheep BSE behaves like scrapie. Scrapie is transmitted from animal to animal and is endemic, and they suspect that BSE in sheep might behave similarly.
The BSE prion shares characteristics with scrapie in sheep. The distribution of BSE infectivity in experimentally infected sheep mirrors that of scrapie and not that of BSE in cattle, with infectivity being present in a wider range of organs. The possibility remains that BSE was introduced in the sheep flock in the mid-1980s and has persisted, says Almond.
The wider distribution of infectivity of BSE in sheep also suggests that effective precautions to protect the public might be more difficult to make than in cattle, and that existing measures might be inadequate if BSE were to occur in sheep.
Slaughter UK measures, based on SEAC recommendations, include the compulsory slaughter of sheep and goats with scrapie with compensation for farmers, and a ban on clinically affected animals - and the heads, spinal cords and spleens of all animals - entering the human or animal food chains. Similar measures have been adopted in France, but not throughout the European Union.
But SEAC acknowledges that, if BSE behaves like scrapie, it "would also be present in the lymph nodes, spleen and parts of the intestine in medium titres in animals in the preclinical phase". "If you wanted to minimize risk you would have in practice to condemn the entire carcass," says Almond.
Almond justifies SEAC's decision to stop short of such drastic recommendations. "To do nothing would be inappropriate," he says, "while banning lamb would be ridiculous." It would not be possible to justify killing the entire national flock when not a single case of BSE had been identified, he says. "We had to find a middle ground, which we call a 'risk reduction strategy' as opposed to a 'risk minimization strategy'."
If new research identified BSE in sheep, SEAC would consider stricter measures, according to one member of the committee, who defends what he describes as an "incremental approach" that adds new measures according to perceived need.
Lack of scientific data on the risks has placed SEAC in a position analogous to that of the scientists who advised the government at the beginning of the BSE crisis, admits one member. "We are back to square one," and "in a very, very difficult position" in recommending appropriate courses of action.
Also in a difficult position is Britain's new Labour government. In its handling of the risk of BSE in sheep, it is in danger of repeating the mistakes made by its Conservative predecessors in their management of the BSE beef crisis, warns the UK Consumers' Association.
The association wrote to Tessa Jowell, the minister of state for public health, on 10 August complaining that the government was not keeping consumers properly informed about the BSE sheep issue, and excessively concentrating decision making in the hands of experts. The confidential letter contests SEAC's recent public recommendation that no further controls - such as a ban on lamb offals - are needed at present.
Sheila McKechnie, the head of the association, argues that SEAC's role should be limited to advising the Department of Health on the state of the science. Public health requires not only a scientific judgement but "a political and social one," she argues, which is the responsibility of government and not experts. "I find this very distressing," says McKechnie, "it is like history repeating itself".
Advice SEAC also needs to explain more clearly to the public the rationale of its advice to government, argues Harriet Kimbell, a lecturer at the Guildford College of Law, and the first consumer representative on SEAC. "The public should be able to make the same informed judgements on their eating habits as I, as a member of SEAC, can." Kimbell claims SEAC is reluctant to make this cultural change - "it is not the most open of bodies," she says. Pattison was unable to be reached for comment on this.
The letter to Jowell also called on the health department to consider advising parents not to feed lamb to young children, "who may not have been exposed to previous risks of BSE and not have eaten lamb so far". The letter argued that until the risk was better quantified this might be justified on the basis of "the public health principle of both precaution and proportionality".
The letter added that the association rejected concerns that "to issue any kind of statement would result in media hysteria and cause major damage to the industry," arguing that this was the policy taken by the previous government. SEAC dismissed the association's suggestion, and DOH has since said it does not intend to issue any further advice at this time.
The quality of the reasoning by some SEAC members is open to debate, however. One member criticizes the association's proposal, arguing that: "If you start saying don't feed lamb to children all hell will break loose." Another says: "I did not understand why children would be at a higher risk than adults, there may be actual reasons to speculate on that, but those would hardly be sufficient to justify such selective precautions."
IN Der Autor meint, dass britische Schafe bis zum Verfütterungsverbot im Juli 1988 mit Fleisch- und Knochenmehl gefüttert wurden. Obwohl also durchaus Schafe unerkannt mit BSE infiziert worden sein können, verfolgt das SEAC nach Auskunft seines Mitgliedes Almond keine Risikominimierungs-, sondern lediglich eine Risikoreduktionsstrategie. Erst wenn BSE in Schafen nachgewiesen werden sollte, will das SEAC striktere Maßnahmen befürworten. Vorbeugender Gesundheitsschutz kommt eben beim SEAC nicht vor den Interessen der Fleischwirtschaft.
MH Animal; Animal Feed; Cattle; Creutzfeldt-Jakob Syndrome/transmission; Encephalopathy, Bovine Spongiform/diagnosis/epidemiology/*transmission; Food Contamination; Great Britain/epidemiology; Human; Public Policy; Scrapie/epidemiology/transmission; Sheep; Sheep Diseases/diagnosis/epidemiology/*transmission
AD Declan Butler (d.butler@nature.com), Nature European Correspondent, Paris
SP englisch
PO England
OR Prion-Krankheiten 2