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Thursday, 10 January, 2002, 12:04 GMT
Q&A: BSE in sheep
So far, no cases of the equivalent of mad cow disease have been discovered in sheep and there is currently no suggestion that infection will break out.
But researchers want to establish the true facts because, they say, the theoretical risk to human health if BSE does exist in sheep is greater than from infected cattle.
BBC News Online answers some questions about sheep and BSE.
What is known about the possibility of BSE spreading to sheep?
It has been shown in laboratory conditions that BSE can be passed to sheep when the animals are injected with infected brain material from cattle.
It is also known that sheep would have been exposed to some of the same infected feed that passed BSE to cattle during the 1980s.
What is not known is whether any sheep were in fact infected, and their symptoms confused with a related disease, scrapie, which has been around for centuries but has never been shown to affect people.
Experiments were conducted in an attempt to establish whether some scrapie-infected sheep actually had BSE. Results were expected in late 2001, but last-minute DNA tests showed the scientists had mistakenly spent three years examining cow brains instead.
What is the latest scientific understanding about sheep and BSE?
A team from Imperial College, London, reported in January 2002 that sheep posed a greater theoretical risk of spreading BSE to humans than cattle.
They said this was because there were more intensive controls in place to protect people against infectivity in beef.
At worst, they said, variant Creutzfeldt-Jacob Disease (vCJD) from sheep could kill 150,000 people, compared with an estimated maximum of 50,000 if beef were the only source.
But they said precautions could reduce the risk from sheep by up to 90%.
The Food Standards Agency says the risk of BSE in sheep remains theoretical, and it is not advising people against eating lamb.
Why would it not be possible simply to ban the infectious parts of lamb, as has been done in cattle?
In fact material such as brain and spinal tissue known to be the main carrier of BSE infection is already banned in sheep products as well as cattle.
The problem is that because of the different anatomy of sheep, infection is distributed more widely throughout the body, so this would not be an adequate safeguard if it were proved that BSE was present in sheep. Hence, the government's contingency plan, announced at the end of last year, to slaughter virtually the entire British flock if it were ever established that BSE was in sheep.
What is the view of this plan from the farming community?
At a time when farmers are still reeling from the impact of the foot-and-mouth crisis, they are naturally alarmed at anything that could create yet another food scare.
However many do recognise the need to avoid the mistakes of the BSE crisis in cattle, and to be more open with the public.
Farmers insist it is highly unlikely that even if some sheep did contract the disease before controls on animal feed were introduced in the late 80s and early 90s, it would still be in the flock today.
If the national flock were destroyed, how would they dispose of 40 million dead animals?
With great difficulty, bearing in mind that this would be roughly 10 times the size of the slaughter in the foot-and-mouth epidemic.
However, unlike the foot-and-mouth outbreak, there would not be the same requirement for speed in the slaughter and disposal of carcasses, since BSE spreads slowly and there would be no risk to people so long as the meat were kept out of the food chain.
The meat and bone meal would eventually be incinerated, but the government is still working flat out to incinerate waste from older cattle banned from the human food chain because of BSE and in the meantime, new storage capacity would have to be found to receive the sheep remains, estimated to amount to around half-a-million tonnes.
How do you rebuild sheep farming, how do you create new flocks?
This would be a long and difficult process. It may be possible to re-introduce sheep which are genetically resistant to BSE, but the contingency plan accepts there is a chance that farms might have to be kept clear from sheep and goats for several years.
This is because unlike BSE in cattle, scrapie in sheep is believed to spread through the environment and can re-emerge when livestock returns to the land.
BSE in sheep might behave the same way. This scenario would not only be the death-knell for Britain's sheep industry, but would have serious environmental implications as large parts of the countryside would remain ungrazed.
Might there be an alternative to wholesale destruction of the entire flock?
Yes, the 40 million sheep slaughter is described as a "worst-case scenario".
It may be possible to identify up to two thirds of the sheep population that carry some resistance to BSE-type diseases and designate them as safe to eat.
It may also be possible to test sheep for BSE at the slaughterhouse or to allow only younger animals into the food chain.
But whether people would be prepared to eat lamb even then remains an open question.
28 Sep 01 | UK
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