New test for BSE in sheep could lead to draconian measures

By Steve Connor, Science Editor

14 April 2003

The scientist who won a Nobel prize for his work on identifying the cause of BSE-like brain diseases has developed a test that will be used by the Government to see if sheep have been infected by "mad cow" disease.

Professor Stanley Prusiner, of the University of California San Francisco, said the test was 100 per cent accurate and could identify animals with BSE long before they showed the first symptoms of disease.

Tissue samples of sheep experimentally infected with BSE are due to arrive at Professor Prusiner's laboratory this week. He will test the material to see if he can distinguish BSE from sheep scrapie, a naturally occurring brain disease which causes the same symptoms as BSE.

If the test works, it will be used to test the brains of thousands of slaughtered sheep to see if BSE has accidentally infected the national flock. If it has, the Food Standards Agency will be forced to introduce draconian health measures to protect consumers.

"This test has been approved for sheep, and we plan to make it available for sheep and there is this question that everybody is very concerned about, is there BSE in sheep?" Professor Prusiner said. "That's a question that has not been answered yet but it will be answered through commercial testing."

The testing will be done by InPro Biotechnology, a company set up by Professor Prusiner, and LGC, formerly the Laboratory of the Government Chemist, in Teddington, south-west London.

Research on BSE in cattle, scrapie in sheep and Creutzfeldt-Jakob disease (CJD) in humans has been seriously hindered by the lack of a test that can identify the earliest stages of infection when there are no outward signs of illness.

Professor Prusiner said the test, called CDI-5, was the first of a "second generation" of tests that will revolutionise the diagnosis and understanding of neurodegenerative diseases caused by rogue changes in the prion protein of the brain. In addition to being used to detect BSE in sheep, the test will be used to ensure that cattle entering the food chain are free of the disease. This will be important if the Food Standards Agency decides to lift the ban on eating cattle over 30 months of age.

Professor Prusiner said the "bioassay" would eventually be developed as a blood test to see if people were incubating vCJD, the variant form of the disease caused by eating BSE-infected meat. "It became clear to me that we needed a better set of tests and in the early 1990s we began to develop this," he said. "The first generation tests are all based on the immunological assays we developed in the mid 1980s."

"The unfortunate thing about all these tests is that they only really reveal the tip of the iceberg." This was because they did not detect the early stage of infection before the onset of symptoms, he said.

"We developed this test and it has some very important features. There are no false negatives [and] there are no false positives... so this gives us increased sensitivity and increased specificity," added Professor Prusiner.

The key to the test's success is that it can distinguish between the two types of the prion protein  the normal and abnormal forms  and is able to quantify how much of each is present.