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- A Nobel prize-winning scientist has warned that there
is increasing evidence that BSE, so-called "mad cow" disease,
is endemic in British sheep.
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- Research by Stanley Prusiner suggests that the infective
prion agent that causes BSE is found in sheep but at levels which have
until now been undetectable.
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- Prusiner, associate professor of neurology at the University
of California in San Francisco (UCSF), won the Nobel prize in 1997 for
discovering prions. Last week he said: "The implication of our latest
work is that BSE is endemic throughout the British national sheep flock."
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- Prusiner's original work described how prions form when
proteins that occur naturally in the brains of all mammals become deformed.
The altered protein then acts as a template, changing other molecules in
a chain reaction that devastates the brain.
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- If an infected beast is eaten, the prions start a similar
chain reaction in the animal that ate it.
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- However, although this mechanism has been well described,
the BSE prion has never been found in sheep.
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- Last week Prusiner said he and Professor Mike Scott,
a Scottish researcher, appeared to have produced BSE in mice by infecting
them with material from sheep suffering from scrapie, which is another
prion disease.
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- Prusiner said: "Our initial data suggests that these
sheep were producing more than one type of prion. One was the scrapie prion
that killed them, but we believe some were also making the BSE prion."
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- The research uses "bovinised" mice, in which
the gene that makes prion proteins is replaced by the same gene from a
cow. Such mice react to BSE prions just like cows, but take less than 10
months to develop the disease, compared with more than three years for
cows.
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- When such mice were inoculated with BSE prions the resulting
disease was identical to that caused by variant CJD prions from humans
- evidence that the prions are the same.
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- The mice were then injected with material from sheep
with scrapie and, again, the incubation and symptoms were close to those
of BSE. This was a powerful indicator that sheep can produce BSE prions.
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- Is it dangerous? Consumer confidence in lamb could be
hit by the warning
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- Fred Cohen, professor of pharmacology at UCSF, said there
was strong evidence that cattle developed BSE because of changes in the
way sheep carcasses were rendered into animal feed.
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- In their latest work, Cohen, Prusiner and Scott replicated
the changes in the rendering process in the laboratory and injected the
resulting material into mice. Cohen said early results suggested that the
theory was correct.
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- "When scrapie-infected sheep were slaughtered, the
rendering process destroyed the scrapie prions but left behind the tougher
BSE prions - to which cattle were vulnerable," he said.
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- If the unpublished results are confirmed, it could have
a serious impact on the sheep industry. There is no evidence that people
can catch BSE from eating sheep, but most research has focused on cattle,
so the possibility cannot be ruled out.
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- The main damage to the industry would come from a loss
of consumer confidence in sheep products. The government has already prepared
contingency plans for testing and slaughtering if BSE should be found in
sheep.
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- BioDemocracy and Organic Consumers Association Activist
or Media Inquiries (218) 226-4164 Fax: (218) 226-4157
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