Britain 'faces Mad Cow epidemic' from infected beef
Pastor Dale Morgan
Britain 'faces Mad Cow epidemic' from infected beef*
By Roger Highfield, Science Editor
Last Updated: 12:01am GMT 10/11/2007
The nation faces the possibility of a major epidemic of lethal brain
disease as a result of the consumption years ago of beef contaminated
with mad cow disease, BSE, according to Britain's leading expert on
vCJD, or "human BSE".
Prof John Collinge of University College London, a Government advisor,
made the comments yesterday when unveiling a new theory of what causes
bovine spongiform encephalopathy, Creutzfeldt-Jakob disease and other
"neurodegenerative" diseases.
Although the incidence of variant CJD in Britain has been declining,
with only four deaths so far this year, Prof John Collinge believes that
only people who are genetically susceptible have succumbed to the
devastating illness so far. "I continue to be worried," he told The
Daily Telegraph.
Official records show that 162 people have died of vCJD, after a peak of
incidence in 2000. But Prof Collinge said that many millions of
infectious doses of contaminated beef were eaten between 1980 and 1996
and there is evidence the disease could silently incubate in a person
for many decades, without producing symptoms.
In a related human disease called kuru the shortest incubation periods
are around five years and he said it was it remarkable that, despite
exposure of babies to BSE in contaminated baby food, there has not been
any cases in a children younger than 12.
That has the "chilling" implication, he said, that the average
incubation period of the cattle disease BSE could be much longer than
kuru, which is not surprising because kuru is a human disease.
Given that kuru can incubate in a person for four decades, he would
expect even longer incubation periods of the cattle disease BSE in
infected people, depending on a person's genetic makeup. "I am afraid
there are a lot more cases in the pipeline," said Prof Collinge.
The key issue - the potential number of cases - cannot be estimated from
the current number of patients. However, based on a preliminary survey
of 12,000 appendix samples scientists would expect around 237 cases per
million, which works out to be some 14,000.
Prof Collinge said, however, that because of uncertainties about the
tests used to detect the presence of CJD, this "could be a considerable
underestimate."
Prof Collinge made his comments while discussing a new theory he has set
out in the journal Science with colleague Anthony Clarke that provides a
new insight into how these diseases kill brain cells.
Most diseases, such as those caused by viruses and bacteria, contain
genetic materials. But BSE and vCJD are caused by a quite different kind
of infectious agent consisting of abnormal proteins. The new theory
shows how prions, the mis-shapen proteins responsible for lethal
diseases such as BSE and vCJD develop in the brain and kill nerve cells.
Earlier work placed emphasis on how abnormal prions convert normal prion
protein in the brain to form damaging lumps of mis-shapen protein,
called amyloid, in a kind of molecular domino effect. However Prof
Collinge provides evidence that this rogue protein itself does not
damage the brain directly.
His new theory focuses on how the abnormal proteins link together and
identifies smaller clumps of the abnormal proteins as the ones that kill
brain cells, not the relatively huge amyloid deposits seen in the brain.
These small toxic molecules represent "the missing piece of the puzzle,"
Prof Collinge said yesterday.
The work is striking because it suggests that other attempts to find
drugs that treat the disease by smashing up the amyloid clumps of
abnormal protein could produce the smaller, more lethal variety.
"Hitting that is not the thing to do."
His team, with the backing of GlaxoSmithKline, is working on drugs that,
in lab tests, could stop the toxic form of abnormal prion from being
made in the first place. Although this effort is still at the level of
basic research, "so far so good," he said.
This drug development work has wider implications, since other
degenerative diseases, such as Parkinson's and Alzheimer's, are thought
to be caused by similar mechanisms.
Thus if this approach can be used to treat CJD, it could work in these
other diseases, which are much more common: around 120,000 people in the
UK have Parkinson's and another 700,000 have dementia.
The theory also explains some scientific puzzles, not least how
abnormally-shaped proteins can spread from one species to another,
crossing the so-called "species barrier," and how they form different
strains of the disease.
"This way of thinking can in principle explain all these different
phenomena," said Prof Collinge.
"This is a fundamental change of thinking and this model fits every
piece of data we have got. Of course, now it is the job of other
scientists to try to falsify this idea."