Britons Alarmed by Report that Mad Cow
Disease May Infect Millions of Sheep

July 23 Sunday Times, London

Top scientist says BSE is in sheep flocks

Jonathan Leake, Science Editor A NOBEL prize-winning
scientist has warned that there is increasing evidence that BSE,
so-called "mad cow" disease, is endemic in British sheep.

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.

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

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.

If an infected beast is eaten, the prions start a similar chain reaction
in the animal that ate it.

However, although this mechanism has been well described, the BSE
prion has never been found in sheep.

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.

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."

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.

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.

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.

Is it dangerous? Consumer confidence in lamb could be hit by the warning

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.

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.

"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.

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.

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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