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Agence
France-Presse
PARIS
- British scientists have cut by more than two-thirds
the projected number of deaths from a brain disorder linked
to eating tainted beef.
Computer
estimates by Oxford University's Wellcome Trust Center
put the maximum number of cases in Britain from variant
Creutzfeldt-Jakob disease (vCJD) at 136,000 over the next
40 years.
The
final toll could be in the hundreds or even as low as
75, depending on the disease's incubation period, it said.
These
figures compare with the center's estimate at the end
of last year that up to half a million people could die.
Estimates by other researchers have suggested a theoretical
toll in the millions.
The
Wellcome Trust team, publishing its findings in Thursday's
issue of the British scientific weekly Nature, said the
big fall was because they believed it may be much harder
for humans to catch the vCJD agent from animals than previously
thought.
"The
current data suggest that, on average, no more than two
cases of vCJD could arise from the consumption of one
maximally infectious bovine," it said, noting that
a year ago, the projected figure was more than 100 cases
per infected cow.
"This
suggests a substantial species barrier (to the infectious
agent), given that thousands of people might eat material
from a single animal."
It
added that the maximum toll of 136,000 would only occur
if the vCJD agent proved to have a long incubation period
of more than 60 years -- in other words, that vast numbers
of people had ate infected beef decades ago but were yet
to exhibit any symptoms.
If,
on the other hand, vCJD had an incubation period of less
than 20 years, the outbreak would soon peak.
In
that case, the total number of cases over the next four
decades would be comparatively tiny, of between 75 and
630.
Researcher
Azra Ghani stressed that vCJD remained a new and still
mysterious disease, which explained the enormous variations
in estimates.
"We
just don't know which of these many scenarios we are going
to end up with," she told AFP.
"It
could either be that there is a strong species barrier
and not many people will be infected, or it could be a
(steady) trickle, an epidemic that is heading upwards
and could be much larger."
These
scenarios, with their outcomes dependent on the incubation
period, are based on there being a tally of at least 15
more cases of vCJD reported this year.
Britain's
Department of Health on Tuesday said the total number
of cases, from Jan. 1 to Aug. 4, was 13, bringing the
total to 79.
In
addition, the Wellcome Trust model is also based on the
assumption that the only people at risk will be those
carrying a genetic sequence known to make them vulnerable
to vCJD, which is about 40 percent of the British public.
That
supposition is contested by some scientists, who say it
may be possible for people without this genetic sequence
to catch the infectious agent and harbor it for years
before they display any symptoms.
The
disease is believed to be caused by eating beef infected
with bovine spongiform encephalopathy (BSE), an ailment
spread by British farmers who fed their cattle ground-up
bodies of sheep which turned out to be infected with a
rogue protein.
The
problem came to light in the late seventies, leading to
measures culminating in 1996 that aimed to stop infected
animals from entering the food chain.
As
its name suggests, vCJD is a form of Creutzfeldt-Jakob
disease, which causes microscopic holes to develop in
the brain, turning it spongy. The victim suffers jerky
movements, forgetfulness, dementia and finally death.
There
is no cure or vaccine for vCJD at present.
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