Mad meat

[Guest guest]

Mad meat

 

British beef may not be the sole culprit in

this long, dark saga

 

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't 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't 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.

 

We also do not know yet how vCJD might spread

from one person to another--so it is possible that

important measures to block such routes of

transmission are not being taken. " In 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, " 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's 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's 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.

 

" What scares me is that BSE in sheep could infect

humans, but look like scrapie, " 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 " perhaps the most important

unanswered question about the BSE epidemic " ,

says Liam Donaldson, Britain's 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--which had always been

free of scrapie--has just declared its first scrapie

cases. Spain denies having BSE, but the European

Commission is sceptical.

 

" The money used for the BSE Inquiry would have

been better spent on eradicating scrapie, " says

Paul Brown of the National Institute of

Neurological Disorders near Washington DC. " The

inquiry won't teach us how to avoid the same

thing happening again. " 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. " We urgently

need to understand how these infections get out

of sheep, " 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--just like Britain

did--though 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. " Evidence so far suggests that the

distribution of prion in humans may be more like

sheep than cattle, " 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's early declarations that beef

is safe for humans, Britain's National Blood

Service says: " There is no direct evidence of blood

transmission of vCJD in humans. " However, this

time someone--Paul Brown--is 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's too late.

 

Debora MacKenzie

 

From New Scientist magazine, 04 November 2000.

 

http://www.newscientist.com/nlf/1104/mad.html