Scientists discover sheep can get BSE. No need to panic, they say. Should we?

Elliot Morley, the minister for animal health, moved swiftly to downplay fears.

He said that the infected sheep was the only one to develop a disease from a group of 19 which had been subjected to a "massive and unnatural" injection of BSE-infected material directly into their brains.

The experiment was carried out by the government-funded Institute of Animal Health at Compton, Berkshire, as part of a 20 million programme of research into transmissible spongiform encephalopathies (TSE) in sheep.

Mr Morley said: ‘‘It has been known for some time that sheep can be infected with BSE under experimental conditions. This result, if confirmed, will tell us nothing more than we already know about the possibility of BSE in the national flock.

"In spite of this result, the fact remains that no sheep of this genotype has been found with a transmissible spongiform encephalopathy in natural, non-experimental, conditions."

Other experts were also quick to soothe public concerns.

George Milne, a development officer with the National Sheep Association in Scotland, said: "This is a research finding in totally artificial circumstances. It has no relevance whatever."

A sheep veterinary specialist said that, with the doses being injected under such artificial conditions, he was surprised that only one of the 19 sheep involved in the experiment became infected.

Although BSE in sheep on farms has never been found, the concern for the government about the possibility is the probable link between the cattle brain infection BSE and the fatal human condition Creutzfeldt-Jakob disease which was made in 1996.

It is now believed that more than 120 people have died from new-variant CJD caused by BSE-infected cattle reaching the human food chain.

Every new revelation about BSE causes a public tremor, no matter how much every organisation and scientist involved tried to play down the appearance of BSE in a single sheep.

Too many members of the public remember a succession of government denials that BSE could have any effect on human health from the late Eighties until the cataclysmic admission in March 1996 that there was a probable link.

As far as the public is concerned, the shorthand of yesterday’s report is that the most resistant of sheep can get BSE, no matter how they get it.

The explanation of why it is extremely unlikely to happen under normal farming conditions, and why a case of BSE has never been identified in Britain’s more than 30 million sheep, takes longer.

It begins with scrapie, a disease of the sheep’s brain and nervous system which has been known for at least three centuries and has never been linked to human infection of any kind.

Nor had there been any serious concern about it. Shepherds knew that some breeds and some flocks within breeds were more susceptible than others, but, as with a range of other diseases, shepherds tended to bury their problems.

BSE changed that. If a TSE in cattle - caused by no-one knows precisely what, except that it is a tiny prion of protein of some kind - could jump species and kill humans, could the same happen with sheep?

There was no record of scrapie ever having killed anyone. But it is very similar to BSE. Could the harmless scrapie be masking the presence, in some sheep, of the much more dangerous BSE?

Laboratory testing began. Tests of sheep brains from slaughterhouses ended in fiasco last year when it was found that scientists had confused containers of sheep and cattle brains. More solid scientific work, funded by the Department of Food and Rural Affairs as part of a 20 million research programme into transmissible spongiform encephalopathies in sheep, has been more successful.

In one experiment five years ago, five grammes of BSE-infected material was fed to genotype-resistant sheep. None has developed BSE.

The work also includes a national scrapie plan for the UK, at present voluntary, designed to eradicate the disease which would, as a by-product, make any future identification of a TSE in sheep easier. More than 260,000 sheep have now been genotyped and more than 7,000 flock owners are taking part with another 11,000 expressing interest.

It is now seen as in everyone’s interest to eradicate scrapie. The plan and research work is based on the fact that 15 separate sheep genotypes have been identified, ranging from the most susceptible to TSEs to most resistant.

In an experiment with a susceptible genotype group, 17 out of 19 sheep succumbed to BSE after a direct injection with infected material and an average incubation period of less than 19 months. So the fact that sheep can be infected with BSE is not new, as Mr Morley was keen to emphasise yesterday.

He said: "It has been known for some time that sheep can be infected with BSE under experimental conditions. This result, if confirmed, will tell us nothing more than we already know about the possibility of BSE in the national flock."

The concern with the news is that the group of 19 were from the most resistant genotype group - ARR/ARR - bred from sheep imported from New Zealand where scrapie is unknown, even if the incubation period was more than 33 months, long past the age when most sheep are slaughtered to be eaten.

A report of the result has been given to the European Commission’s animal health committee, which is working on an EU scrapie plan.

It will also be considered by a sub-committee of the spongiform encephalopathies advisory committee on 11 December, which will report back to ministers on any possible implications for the national scrapie plan.

Trouble on the farm: a disease factfile

What is Bovine Spongiform Encephalopathy?

A brain and nervous system disease in cattle which was first identified in 1986. Ten years later, it was linked to the human brain infection, Creutzfeldt-Jakob disease. More than 120 variant-CJD deaths so far have been linked to eating BSE-infected meat before stringent controls were introduced.

What is scrapie?

Scrapie in sheep shows similar symptoms to BSE, but was first identified three centuries ago and has never been linked with any human infection even when potted head and sheep’s-head broth was a regular part of the British, especially Scottish, diet.

Can sheep get BSE in normal farming conditions?

Not as far as we know. But the concern is that the infections are so much alike - the precise cause of these and other transmissible spongiform encephalopathies has never been established - that scrapie could be masking BSE.

But sheep can be infected with BSE under experimental conditions?

Almost any species could, theoretically, be infected by massive doses of BSE-infected material injected directly into its brain. It could be argued that only one animal out of 19 getting the disease has indicated the strength of that genotype’s resistance.

What would happen if a sheep was found to have BSE under normal farming conditions?

It would be devastating. Several million cattle have been slaughtered and burned to prevent them reaching the human food chain during the BSE eradication programme since 1996, and a similar operation would have to be implemented for sheep.

Should sheep farmers and the public be optimistic?

Yes. More than ten years ago, it was proved that pigs could be infected with BSE if a big enough injection of infected material was used. There has never been any question of pigs having BSE under natural conditions.