US: A blood test for the rogue proteins that cause BSE, or "mad cow disease", has been developed by US scientists, raising hopes that people could soon be screened for the human form of the condition, vCJD.
The breakthrough could protect patients receiving blood transfusions and organ transplants, and help experts to predict the size of any future vCJD epidemic.
About 180 people worldwide have died from variant Creutzfeldt-Jakob disease, which is linked to eating BSE-contaminated meat. Scientists warn there could be many more deaths in the coming decades because the disease has an incubation period of up to 40 years.
There is currently no reliable way to detect BSE or vCJD in blood, with the diseases only confirmed after death.
The US team, led by Claudio Soto at the University of Texas Medical Branch, says it can find the infectious "prion" proteins behind such diseases in the blood of experimental animals. The researchers are now refining the method to find prions in people who died from vCJD, using blood samples from British victims.
Prof Soto said: "We believe in six months or so we should have the technology optimised to detect prions in human blood. The next step is to make sure we can detect them in blood before the clinical symptoms appear." Finding a test to detect prion diseases like vCJD and BSE developing in apparently healthy animals and people has proven difficult. A blood test would be the simplest way to screen donors and keep infected meat from entering the human food chain, but the prion concentration in blood is too small for it to be detected by existing techniques. Prof Soto's team has taken a different approach, using a biochemical trick to amplify the quantity of prions in diseased blood millions of times, making them easier to find.
Prof Soto said: "The concentration of infectious prion protein in blood is far too small to be detected by the methods used to detect it in the brain, but we know it's still enough to spread the disease. The key to our success was developing a technique that would amplify the quantity of this protein more than 10 million-fold."
Other prion researchers have found it difficult to replicate the technique.
Writing in the journal Nature Medicine, the Texas researchers say they used the method, known as protein misfolding cyclic amplification, to screen blood from 18 prion-infected hamsters, which had developed symptoms. The scientists found prions in the blood of 16 of the 18 infected hamsters, with no prions found in 12 healthy ones.
The technique - similar to one used by forensic scientists to amplify fragments of DNA found at crime scenes - uses sound waves to vastly accelerate the process that prions use to convert normal proteins to misshapen infectious forms.