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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