Accurate blood test for mad cow disease in humans developed

SCIENTISTS in Britain have developed the most accurate blood test yet for the human form of mad cow disease, but a more generally applicable screening test for a healthy population is still some way off.

Researchers at University College London (UCL) have developed a test prototype which is 100,000 times more sensitive than previous methods, capable of detecting tiny amounts of variant Creutzfeldt-Jakob disease (vCJD)-causing particles, or “prions”, in human blood.

The British research team tested 190 blood samples, including 21 from people known to have vCJD.

The prototype blood test was able to detect blood spiked with a dilution of vCJD to within one part per 10 billion — 100,000 times more sensitive than any other method developed so far. Medical circles have been enthusiastic about the progress.

William Heaton, a transfusion specialist at the North Shore-LIJ Health System in the US, said: “The detection rate is impressive. This represents a great start, and all involved with screening for this disease should be excited by this development.”

However, as the human fluid for these tests can only be obtained by lumbar puncture (spinal tap), the new test is really only suitable for people already unwell with a nervous system condition. Researchers globally are still seeking a more broadly applicable screening test.

As Dr Ian Franklin, medical and scientific director with the Irish Blood Transfusion Service (IBTS), explains: “There is no routinely available test for variant CJD at present. The types of tests that are used to screen blood and tissue donations for viruses cannot be applied to variant CJD because it is a different type of disease. Several international groups of research workers are working to develop a blood test, but it is unclear when a test suitable for blood donor screening will be available.

“In the past month, two tests have been unveiled that may help in diagnosing people who have variant CJD. One of these, from the USA, requires samples of cerebro-spinal fluid to be effective.

“This fluid can only be obtained by lumbar puncture. Therefore, it is only suitable for people already unwell with a nervous system condition.

“The other test was published in the Lancet by a team from University College, London. This uses blood samples but as described by the authors, is suitable only for studies in patients who may have variant CJD.

“A screening test that could be applied to healthy populations would be very useful but has remained elusive. It is not even possible to suggest when such a test will be available as a number of tests have looked promising in the past but then proved to be unsuitable for this use. So even interesting tests described like these recent ones may not be any value for screening healthy people.”

Experts say the disease affects about one person in every million per year worldwide, but prions, the infectious proteins which cause vCJD, can inhabit a person’s body for up to 50 years before presenting symptoms.