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Linklater's Scotland:
BSE and the great scare of nvCJD
Magnus Linklater
Columnist, Scotland on Sunday
Filed 30 Jun 06
©Magnus Linklater
This article,
which was originally published in the Spectrum Magazine of
Scotland on Sunday on 25th June 2006, is reproduced on Land-Care
with the kind permission of the author and the newspaper
TEN years ago, a new strain of human brain
disease was identified, and it sparked one of the great medical
scares of modern times. New variant Creuzfeldt Jakob Disease was
not only a degenerative and incurable infection of the brain, it
was linked to the outbreak, a decade earlier, of a similar disease
in cattle - BSE. In 1996, after months of foot-dragging, John Major's
government was finally forced to announce that vCJD could be caused
by eating contaminated meat.
The statement led to the virtual collapse
of the British beef industry, an export ban, a cost of some £3.5
billion and - since thousands of people in Britain had been exposed
to the risk by eating infected beef - the possibility of a serious
pandemic. Newspaper headlines spoke of hundreds of thousands of
deaths from this deadly disease. Even scientists analysing likely
models for the outbreak admitted that up to 80,000 people could
die.
Last week I visited the website of the National
CJD Surveillance Unit to check the latest figures. It showed that
last year precisely three people died from vCJD. The total number
of deaths since 1995 is 156, and the yearly figure has been in steady
decline since 2000 - when 28 people died. Whatever happened to the
great epidemic?
The headquarters of the surveillance unit
is an anonymous office block at Edinburgh's Western General Hospital
and is run by Dr Richard Knight, a 55-year-old clinical neurologist.
His job is to monitor the progress of the disease, to plot how or
whether it is changing and to inform scientists, and ultimately
the public, if we are at risk. He is not only responsible for the
UK's state of knowledge on the various strains of CJD, he also co-ordinates
research across Europe.
Why are the figures falling? With refreshing
candour, he admits, "We do not know." But the more he
describes the complexities of the disease, the accepted scientific
definition of its nature and the dominant theory that links it to
cattle, the more I begin to question whether we might not have got
the whole thing badly wrong, and to wonder whether there really
is any connection between the cattle and the human disease. Could
this have been the scare that never was?
This is not the way Dr Knight sees it. He
believes that BSE and vCJD are the same strain of disease, and until
someone comes up with a better explanation for how it is passed
on, he sticks with the idea that the two are linked. "My approach
is rigorously empirical," he says. "I am wedded to the
principle that any scientific fact is simply a truth until the next
experiment proves it to be false. When I say that BSE is the cause
of vCJD, I have to be open to the idea that it may be proved false.
But there is little doubt that there is a relationship between the
cattle disease and the human disease, and all the facts point towards
BSE as being the cause of vCJD. I know of no good evidence for any
alternative."
The entire thesis rests on one of the most
controversial scientific discoveries of recent times. In 1997, Stanley
Prusiner, professor of neurology at the University of California,
was awarded a Nobel Prize for proposing that the cause of brain
diseases such as CJD, scrapie in sheep and BSE in cattle was a new
type of infectious agent - not a virus or a bacterium, but a protein.
He called these proteins prions, or proteinacious infectious particles.
Unlike other agents, prions have no genetic
material, which makes them the only lifeform that can multiply without
a gene. Prusiner says they enter the body through food, thus setting
off a chain reaction, converting normal proteins into abnormal ones,
creating deposits that cause irreversible brain damage. Radical
as the idea is, it has gradually been winning support, becoming
today the accepted explanation for these diseases.
But there have always been doubters - maverick
scientists like Professor Alan Ebringer, or the Somerset farmer
Mark Purdey, who claim to have discovered other, more conventional
causes of the disease. In recent years these doubts have grown,
in the pages of medical journals. Researchers say they have been
unable to replicate Prusiner's findings using laboratory-made prions.
Experiments with sheep, given food heavily contaminated with abnormal
prions, showed that the animals simply digested them, with very
few of the prions surviving. It seems possible that another, unidentified
agent might be responsible for the disease. Even more challenging
is the suggestion that the abnormal prions might be the consequence
of the disease rather than its cause.
To all of this, Dr Knight responds with
measured caution. He says that there may be different reasons for
the fact that so few deaths have occurred. First, the numbers, as
reported in the press, were far too high. "The outlandish predictions
were never likely to be realised," he says. "Even 80,000
was an upper limit, and we never seriously expected it to reach
that level. Those figures should not be taken seriously."
Second, some people may have a genetic disposition
to the disease while others do not, thus eliminating thousands who
might otherwise have caught it. Then there is the long incubation
period - as much as 40 years, which means that a victim may be infected,
but is likely to die of other things long before the disease catches
up with them. "Some people may have been infected, but have
not yet become ill because the incubation period is so long,"
he says. "We are not sure about this because we have no pre-clinical
tests. Then there is the possibility of the sub-clinical disease
- that is, someone becomes infected, but it never develops into
the full-blown disease."
But what about the possibility that the
prion theory is simply wrong, that for more than a decade we have
simply been pursuing the wrong trail? Dr Knight's reply is surprisingly
equivocal. "The burden of proof now rests with the opposition,"
he says. "Someone has to come forward with an alternative.
No one has done it. I'm an agnostic on the prion theory. I don't
know what the cause of the prion disease is, but it is the dominant
theory, and it explains an awful lot. The empirical data is difficult
to explain, however. The disease occurs with high levels of infection
and low levels of prion."
So could there be another cause of the disease?
"It is possible for the prion theory to be false, but for the
cattle disease still to be the cause [of vCJD]," he says. "It
is possible that there is another agent involved, but I do not know
anyone who has come up with an alternative."
He concedes that because prions have no
genetic code it is hard, if not impossible, to codify different
strains of the disease in cattle and humans. "The prion theory
has not yet been fully proved," he says. "It might be
proved wrong. It is simply a theory about the nature of the infectious
agent, but it does not have an adequate explanation of strain behaviour.
The prion protein theory explains an enormous amount, but it fails
to explain certain things adequately. There is an important piece
missing."
The scientist who finds that piece could
well be on the way to winning another Nobel Prize. In the meantime,
though, we can simply give thanks that a killer disease is on the
wane and that we can continue to eat beef and mutton without a qualm.
©Magnus Linklater
Further reading recommended by Land-Care
 1.
Wilson, C., Hughes, L.E., Rashid, T.,
Ebringer, A. and Bansal, S. (2003).
Antibodies to Acinetobacteria and bovine brain peptides, measured
in Bovine Spongiform Encephalopathy (BSE) in an attempt to develop
and ante-mortem test.
J. Clin. Lab. Immunol. Published online 13 March 2003
2.
Irvine, James (2006). EU vets voted unanimously to lift the ban
on the export of UK beef.
See SOCIAL/ECONOMIC/Political Homepage, filed 11 Mar 06,
www,land-care.org.uk
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