CONSUMERS in Ireland last week became the first shoppers to be given the
option of buying beef tested for BSE. But there is no evidence that the test can
identify carcasses of infected animals which have not yet developed symptoms.
And while the supermarket chain involved is careful not to claim that the tested
meat is 鈥淏SE free鈥�, scientists fear that the public may assume that this is the
case.
The BSE test being used by SuperValu stores is marketed by the Irish company
Enfer Scientific. The diagnostic technology is licensed from Proteus
International of Macclesfield.
After a cow is slaughtered, a sample of tissue from its central nervous
system is treated with enzymes which digest the normal form of the PrP protein
that becomes misshapen in cows with BSE. The sample is then mixed with
antibodies that bind to the remaining PrP, which must be of the rogue 鈥減rion鈥�
form. Each antibody molecule is bound to a fluorescent dye, so the sample glows
if it contains large quantities of prion.
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The sign in SuperValu鈥檚 168 stores reads: 鈥淪uperValu leads the field of safer
beef. That鈥檚 why we鈥檙e the first to introduce Enfer Scientific testing to ensure
the highest standards of safety for our beef.鈥� A photo of a joint of beef is
stamped with the words: 鈥淪uperValu 100 per cent Enfer tested.鈥�
Beef that has been tested is priced at up to 10p a kilogram more than
untested beef. It is too early to tell whether the move will boost beef sales,
but a spokesman for SuperValu says the initial reaction from customers has been
鈥渧ery positive鈥�.
The test has been validated by Ireland鈥檚 Department of Agriculture. A
statement from the department says the test showed 鈥渆xcellent discrimination鈥�
between tissue samples from cattle with clinical symptoms of BSE and those
without the disease. But it adds that it is not yet clear if the test can
identify carcasses of infected animals which have not developed symptoms.
BSE experts say that knowing the stage of infection at which a test can
identify an animal that will succumb to BSE is crucial. Animals with symptoms
should be excluded from the food chain anyway, they point out. Ray Bradley, an
independent consultant on BSE who formally worked at the Central Veterinary
Laboratory in Weybridge, Surrey, says that a test that can鈥檛 identify animals
incubating BSE is 鈥渟uperfluous鈥�.
鈥淯nless Enfer can transparently explain the basis of claims to a validated
test, then I think one should rightly ask what it means,鈥� says Chris Bostock,
director of the Institute for Animal Health in Compton, Berkshire.
Determining whether the test can identify animals incubating BSE would
require a group of cows to be deliberately infected, with individuals
slaughtered at intervals to determine when the test can pick up infection. These
experiments have not yet been done.
Enfer has a temporary exclusivity arrangement with SuperValu, but is already
in discussion with British retailers. 鈥淚t could act as a significant reassurance
to our customers,鈥� says a spokesman for Sainsbury鈥檚. 鈥淗owever, we must be 100
per cent confident of its accuracy and robustness.鈥�
John Pattison of University College London, who chairs Britain鈥檚 Spongiform
Encephalopathy Advisory Committee, says that his committee has repeatedly asked
for details of the test鈥檚 validation but has yet to receive them. Riona Sayers,
project leader at Enfer, expects the results to be published within six months,
once the company has obtained a patent.