THE whole point of the BSE Inquiry was to learn from past mistakes. But can
we be sure that a similar food and health disaster won鈥檛 happen again?
The simple answer is no. We know that BSE rampaged through British cattle,
and we are now seeing the beginnings of an outbreak of vCJD in people. But we
know so little about where else BSE might have spread that we simply can鈥檛 say
whether meat is safe. Mutton, lamb, pork and even chicken may harbour the
infection. And we may be repeating those past mistakes that allowed BSE in
cattle to spiral out of control.
The problem is not confined to Britain. France and Portugal are just
realising that they have far more BSE cases than they thought, and similar nasty
surprises probably await other countries in Europe
(see Graph). Cases of vCJD
have already appeared outside Britain.
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We also do not know yet how vCJD might spread from one person to
another鈥攕o it is possible that important measures to block such routes of
transmission are not being taken. 鈥淚n terms of what we know about the disease,
we might be at the same stage in the vCJD epidemic now as we were with BSE in
the early days,鈥� says Moira Bruce of the Neuropathogenesis Unit in
Edinburgh.
What we do know is that pigs, chickens, sheep and even farmed fish have been
exposed to BSE-contaminated feed. In many places in Europe, and possibly
elsewhere, they still are. Britain banned the rendered remains of mammals from
all animal feed in 1996. But elsewhere in Europe, where there are small but
significant numbers of BSE-infected cattle, this material can legally be fed to
non-ruminants. European Commission scientists believe some is still reaching
ruminants as well.
Moreover, some countries that could well harbour BSE-infected cattle will
only start removing key infected tissues, such as brain and spinal cord, from
animal or human food this year. But scientists recommended removing high-risk
tissue from cattle in all EU countries in 1997, says Albert Osterhaus of the
University of Rotterdam, a member of the European Commission鈥檚 advisory panel on
transmissible spongiform encephalopathies (TSEs).
It is also now clear that infections such as BSE affect different species in
radically different ways. One species can be infected with a prion and not show
any symptoms. But it can pass the infection to another species, which then falls
sick.
There has been, for example, no visible outbreak of TSEs, the group of
diseases that include BSE, in pigs and chickens. Researchers working for
Britain鈥檚 Ministry of Agriculture, Fisheries and Food have failed to cause
disease in pigs and chickens by giving them BSE-contaminated feed. This may mean
such meat is safe. Crucially, however, no one has reported putting tissue from
pigs or chickens that ate BSE-contaminated feed back into cows or other animals,
to show if they are nonetheless infectious.
Sheep are another matter. When they eat BSE-contaminated feed, they develop a
disease clinically similar to the sheep disease scrapie. Mice fed meat from such
sheep develop the distinctive pathology of BSE. So these sheep still have BSE,
which, unlike scrapie, is a potential human pathogen.
鈥淲hat scares me is that BSE in sheep could infect humans, but look like
scrapie,鈥� says Osterhaus. Scrapie is common in much of Europe. We would not
realise such sheep were dangerous, so people could be eating animals that are
infected but not yet sick. This is 鈥減erhaps the most important unanswered
question about the BSE epidemic鈥�, says Liam Donaldson, Britain鈥檚 current Chief
Medical Officer.
It has taken a while for researchers to realise the risk. They are now
checking to see whether sheep with scrapie-like symptoms are actually harbouring
BSE. Ominously, Spain鈥攚hich had always been free of scrapie鈥攈as just
declared its first scrapie cases. Spain denies having BSE, but the European
Commission is sceptical.
鈥淭he money used for the BSE Inquiry would have been better spent on
eradicating scrapie,鈥� says Paul Brown of the National Institute of Neurological
Disorders near Washington DC. 鈥淭he inquiry won鈥檛 teach us how to avoid the same
thing happening again.鈥� British agriculture minister Nick Brown says Britain
plans to eradicate scrapie just in case it is masking the presence of BSE.
Another problem with sheep is the distribution of infection in their bodies.
In cattle, BSE is only known to infect brain and nerve tissues and some parts of
the gut, says Bruce. But in sheep with BSE, as in scrapie, infection is spread
through the body, and is more likely to be in the meat we eat.
This means that unlike BSE in cattle, BSE in sheep might well spread from
sheep to sheep when they nibble afterbirths or dead sheep. Controlling feed will
not block infection in this case. 鈥淲e urgently need to understand how these
infections get out of sheep,鈥� says epidemiologist Mark Woolhouse of the
University of Edinburgh.
Although progress has been slow, the one area where we seem to have learned
the lesson of the BSE debacle is research. This time, say scientists, research
efforts are open, and broad-based, and the threat to public health is
concentrating minds on the key risk areas.
Yet government reluctance, especially in continental Europe, to admit the
scale or implications of the BSE epidemic still hampers progress. The German
government continues to promote German meat as safe鈥攋ust like Britain
did鈥攖hough few experts believe Germany is free of BSE. EU countries are
only now preparing to test cattle not obviously suffering from BSE for the
prion. This has already revealed many unsuspected cases in France and
Switzerland. But Markus Moser of the Swiss company Prionics, which makes one of
the leading tests, says some countries have not yet published their plans to
test cattle.
We have also been slow to realise that TSEs may spread from person to person,
for example, in blood products. 鈥淓vidence so far suggests that the distribution
of prion in humans may be more like sheep than cattle,鈥� says Bruce. Unlike
cattle, it seems that BSE in infected sheep can pass into other sheep through
blood. If humans are similar, transfusions might pose a risk.
Yet in a recent statement eerily similar to the British government鈥檚 early
declarations that beef is safe for humans, Britain鈥檚 National Blood Service
says: 鈥淭here is no direct evidence of blood transmission of vCJD in humans.鈥�
However, this time someone鈥擯aul Brown鈥攊s testing blood transmission
of vCJD in primates to make sure.
So once again, we may be allowing a BSE-like disease to spread. This time,
far more scientists are interested and far more people are watching for the
unexpected pathways BSE might have taken. We can only hope that this time, they
get it right before it鈥檚 too late.
