Britain is to step up its efforts to discover whether bovine spongiform encephalopathy (BSE) is present in the national sheep flock. Some experts fear that the disease may exist in sheep but that it is mistaken for scrapie, which is endemic in the flock.

David King, the government's chief scientific adviser, announced that the government will test thousands of scrapie cases for the agent that causes BSE. The move, which critics say amounts to a reversal in government policy, follows last month's controversy over whether researchers in another experiment had spent five years accidentally testing cow brains instead of sheep brains for BSE (see Nature 413, 760; 2001).

The new project revives a proposal made three years ago to use a cheap technique that distinguishes between strains of prion protein by revealing their conformations and glycosylation patterns. The test takes just 48 hours.

Until now, UK government experiments on BSE in sheep have relied exclusively on conventional strain typing, which discriminates prion strains well but takes two years to complete because it requires analysis of incubation times and lesion profiles in mice inoculated with sheep extracts. As a result, only 180 sheep brains have so far been tested.

King said he was “confident” that the tests will gather a significant amount of data in a short time. But he added that, because the test was still being validated by the government's Veterinary Laboratory Agency, it would take “months, rather than weeks to be statistically certain that there is no BSE in sheep”.

The test to be used was developed in 1996 by John Collinge of Imperial College School of Medicine in London, a member of the UK government's Spongiform Encephalopathy Advisory Committee (SEAC).

But some scientists are sceptical of the test's ability to distinguish scrapie and BSE. For example, a group at the Institute of Animal Health near Newbury, Berkshire, has reported that one scrapie strain, CH1641, gives a similar glycosylation pattern to BSE.

SEAC nonetheless said in 1999 that glycoform profiling should be a high priority. Collinge complains that the Department for Environment, Food and Rural Affairs (DEFRA) has not used the test enough to improve its distinguishing power. But Oliver Cattermole, a DEFRA spokesman, says that the validation process is time-consuming, and adds that the test is “not the be all and end all” of sheep BSE research.