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Prototype blood test for vCJD

Fergus Walsh | 14:34 UK time, Thursday, 3 February 2011

Variant Creutzfeldt-Jakob disease is a terrible legacy of the BSE outbreak. The fatal degenerative brain disorder is the human form of Bovine Spongiform Encephalopathy, commonly referred to as "mad-cow disease". It first emerged in 1995. The disease, which affects the brain, is believed to have passed from cattle to humans through consumption of meat products contaminated with BSE.

The issue gets little publicity these days, but news in The Lancet medical journal of a prototype blood test for the condition is a significant moment. Researchers at the Medical Research Council Prion Unit at University College London have managed to devise a test which can spot the infectious proteins - prions - responsible.

The blood test was able to detect blood laced with a solution of vCJD to within one part per ten billion. It was around 70% accurate, so clearly there is work still to do, but the scientists are confident that accuracy will improve rapidly in the near future.

An accurate blood test would have far-reaching implications. Firstly, it would speed up diagnosis. Patients with vCJD are usually diagnosed late, only when they have begun to display symptoms. A sample of tonsils can usually tell doctors if they infected, but for a definitive diagnosis, a biopsy of brain tissue is required. So a blood test would mean simple and rapid diagnosis.

It would also provide the first accurate assessment of the extent of vCJD in Britain. This is a disease which began in Britain and most of those affected are here: out of 220 cases worldwide, 174 are British. Four of the British patients are still alive. Cases outside Britain are likely to be a significant underestimate, because doctors elsewhere often don't actively look for the condition.

Prions, which cause vCJD and other fatal diseases, can inhabit a person's body for 50 years before presenting symptoms. So there has always been a suspicion that the true scale of the vCJD infection has remained hidden. A study of tonsil samples suggested that 1 in 4,000 Britons might have the disease, but no-one really knows whether that is an accurate estimate (opens pdf). One positive fact is that the number of deaths from vCJD has been falling steadily since a peak of 28 in 2000.

An accurate blood test would also have implications for the National Blood Service. Currently, white blood cells are removed from donations and plasma products are imported. Blood donations are screened for HIV and Hepatitis B and C. If detected, donors are advised to speak to their doctor. But what if you were found to be infected with vCJD? If the test was not 100% accurate then it would raise the issue of so-called false-positive results. A commentary on the Lancet article says: "Communication to the public of the uncertainty around a positive test result will be challenging and could result in fewer donors as well as causing unnecessary anxiety to deferred uninfected donors."

The knowledge that you are harbouring vCJD, would be an extremely difficult issue to address. Some of those identified might never go on to develop to condition, so would have to confront an issue they would otherwise never have to face.

Variant CJD is a fatal condition for which there no proven treatment - although a number of experimental therapies have been tried. But there is scope for optimism here as well. Professor John Collinge, Director of the MRC Prion Unit was interviewed on Today on Radio 4 (listen again here). He said his team has been able to create human antibodies to the prion protein which blocked the disease in mice. Human clinical trials will begin in due course. Professor Collinge said: "There is an opportunity if we find people who are incubating the disease, in principle, to rescue them before they develop the disease itself."

That really would be a remarkable achievement.


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