British scientists have made a prototype of the most accurate blood test yet for the human form of mad cow disease, and say their work could transform diagnosis and screening of the fatal brain disorder.
In an early-stage trial, the prototype, which is 100,000 times more sensitive than previous methods, was able to detect tiny amounts of variant Creutzfeldt-Jakob disease (vCJD)-causing particles, known as prions, in human blood, the scientists said.
"Although further larger studies are needed to confirm its effectiveness, (this test) is the best hope yet of a successful early diagnostic test for the disease," said Graham Jackson, who led the study at the Medical Research Council's Prion Unit at University College London (UCL).
He said it could in future allow doctors to screen whole populations for vCJD infection, assess how many people are silent carriers and prevent onward transmission of the disease.
Variant CJD first emerged in the mid 1990s and is the human form of bovine spongiform encephalopathy (BSE), commonly known as mad cow disease.
The disease, which affects the brain, is thought to have passed from cattle to humans through infected food. It causes personality change, loss of body function, and eventually death.
World Health Organization data, which only go up to 2002, show that from October 1996 to November 2002, 129 cases of vCJD had been reported in Britain, six in France and one each in Canada, Ireland, Italy and the United States.
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.
During this time, a vCJD carrier could pass it on to others, possibly through a blood transfusion or through medical instruments, since prions can easily attach onto metal surfaces.
"One of the reasons that vCJD is such a dreaded disease and has caused such disruption and expense to health services is the lack of knowledge of who is and who is not a carrier of this infection," said John Collinge, director of UCL's Prion Unit.
The 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.
Commenting on the results, which were published in The Lancet on Thursday, William Heaton, a transfusion specialist at the North Shore-LIJ Health System in the United States, said the detection rate was "impressive."
"This represents a great start, and all involved with screening for this disease should be excited by this development," he said in an emailed statement.
Collinge said the next step would be to test several thousand blood donors anonymously from a country not affected by BSE to get a better idea of how the test performs in practice.
Longer-term studies will also be needed to assess what proportion of people who test positive for prion infection go on to develop the disease later in life, he said.