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Super-sensitive BSE tests may not make meat safer
19 January 2008
From New Scientist Print Edition.
Debora Mackenzie

Europe is winning the battle against BSE, eight years after it exploded across the continent. The ban on feeding meat and bonemeal to animals has halted the spread of infection, and last year a mere 49 animals tested positive at slaughter in the UK. Now the European Commission wants to ease up on controls and the number of cattle undergoing expensive tests. Will this put people at risk?

ProMetic, a Canadian company that has developed a super-sensitive BSE test, argues that we must impose the most stringent tests possible on cattle because we know so little about the disease. A new generation of tests may be about to gain approval from the commission, including ProMetic's, which is 80 times more sensitive than existing tests.

However, many scientists argue that while such tests may reveal more infected animals, they may not necessarily make meat any safer for people to eat.

At the moment every cow over 30 months old in the EU destined for the table is tested at slaughter for BSE. Infected younger cattle are rare - tests found no infected animals under 35 months old in 2006, and only one in 2005, at a cost of €320 million. To save money, the EC wants to increase the age limit for testing.

This may be difficult to justify if more sensitive tests start finding infected younger cattle. ProMetic's test uses a resin which selectively binds to the prion protein involved in BSE. While they hope to use their test to remove prions from donated human blood, the binding process effectively concentrates any prions present in a sample, so it can also make existing cattle tests for prions more sensitive.

Ultimately, ProMetic wants to develop a test sensitive enough to detect prions in live animals and in people, says Peter Edwardson, the company's chief medical scientist. In the meantime, as the resin boosts the sensitivity of slaughterhouse tests on cattle brain, they can give a positive result for dead cattle that would otherwise have tested negative. "This means we can detect infected animals earlier in the disease," says Edwardson.

Some question whether this will make meat any safer. "It would be great for research," says Marcus Doherr of the University of Bern in Switzerland. But existing tests detect prion material in cattle brain when there is not enough to infect people with vCJD, the human form of BSE.

Markus Moser, CEO of the Swiss firm Prionics, the leading manufacturer of BSE tests, agrees that more sensitive testing at slaughter is unlikely to make meat safer. "Once prion reaches the brain, its levels rise very fast. There are probably not a lot of cattle around with lower levels that would turn up on such tests."

By identifying more infected animals, says Doherr, highly sensitive tests would prolong the agony, and the expense, for countries trying to get rid of BSE - with little benefit to public health.

Edwardson disagrees. "Until someone can prove that these animals pose no risk to people, we should not let our guard down."

From issue 2639 of New Scientist magazine, 19 January 2008, page 12

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