http://www.guardian.co.uk/bse/article/0,2763,1040376,00.html
Scientists investigate BSE tests on sheep

Urgent look at 'puzzling' results as farms fear new blow

James Meikle, health correspondent
Friday September 12, 2003
The Guardian


Scientists are to urgently assess whether the nightmare scenario of BSE crossing from cattle to sheep on Britain's farms has already happened, it emerged yesterday. Experts are likely to meet within a fortnight to study "puzzling" and "interesting" results from a huge survey of samples from sheep brains that would - if confirmed - spell another disaster for public confidence in meat and British agriculture.

They are expected to order further laboratory tests but it might be months before any firm conclusions can be drawn about unexplained results in 28 of nearly 30,000 samples. European food safety authority advisers will also be involved.

Three main options are being examined:

that there was a problem with the testing method;

that these results confirm the existence of scrapie, a naturally occurring BSE-like sheep disease never known to have endangered humans;

that, most explosive of all, BSE, already blamed for killing 136 Britons through food, has spread naturally from cows to sheep.

The chairman of the food standards agency, Sir John Krebs, yesterday told his board of directors: "Our advice to consumers remains the same. We are not advising against the consumption of lamb and sheep meat."

The government is reviewing contingency plans for a sheep catastrophe, long recognised as a theoretical risk. These are believed to include changing the way sheep meat is prepared for food, culling infected animals and other possible contacts, and, in the most drastic resort, destroying virtually the whole national flock of 36m animals.

Tests on sheep infected experimentally with BSE in the laboratory suggest the disease infects far more tissue than it does in cattle, thus making removal of tissue potentially dangerous to people eating meat far more difficult.

However, farmers are suspicious of BSE and scrapie research, especially following the collapse two years ago of crucial experiments meant to check sheep brains for evidence of BSE. It emerged that these were far more likely to have been cattle brains wrongly stored and labelled years before.

The European Union has insisted on more testing of sheep for BSE-like diseases, known as transmissible spongiform encephalopathies, or TSEs. As part of this, material from sheep brains collected from abattoirs has been screened by a rapid test which can be completed overnight. However, this Biorad test has only been formally approved by the EU for tests on cattle, not for sheep.

That means quick tests which reveal positives have to be confirmed by more complicated tests, using a different part of the brain, which can take up to three weeks. In these, tissue is stained to show up the abnormal prion protein characteristic of scrapie. The 52 rapid test results which suggests the presence of scrapie or similar disease were double-checked. In 28 of these extra tests there was no sign of any problem at all.

Sir John said: "This is a puzzling result. It could mean one of several things. It could be a problem with the test and not with the sheep. The test may give false positives. It could be scrapie. The Biorad test might be more sensitive at picking up scrapie than the staining method. It could be a different TSE, possibly even BSE, detected by the Biorad test and not by testing.

"These results do not appear to look the same as when sheep have been experimentally infected with BSE. However, scientists do not know what BSE in sheep would look like, were it to be transmitted from sheep to sheep."