A sensitive urine test can identify the human form of mad cow disease in people showing no symptoms.
The new test for variant Creutzfeldt-Jakob disease (vCJD) could be used to screen individuals who may unwittingly be carrying the infection, according to research published in the New England Journal of Medicine.
It could also help to ensure the safety of donated blood, which can transmit the rogue proteins linked to the disease.
“It opens the door to the development of a screening tool for people infected with CJD who do not show any symptoms”
Experts have spent decades searching for an effective way of diagnosing variant CJD in people while they are alive.
Currently the only certain way of establishing the presence of the disease is by examining brain tissue.
Variant CJD, which progressively destroys the brain and is always fatal, caused a major health scare when it first emerged in the UK in 1986.
Scientists learned it was basically the same infection that caused bovine spongiform encephalopathy (BSE) in cattle.
The disease jumped into humans through the consumption of infected meat, notably beef burgers.
It could also be transmitted via contaminated surgical instruments and blood transfusions.
Despite fears of a terrifying epidemic, the disease proved very rare. Variant CJD has killed 229 people since it was first identified, including 177 from the UK.
But the infection can lie dormant for many years – possibly decades – before causing any symptoms, and may even incubate for longer than a person’s normal life span
It has been estimated that up to one in 2,000 people in the UK may be carrying the misshapen prion proteins believed to cause the disease.
The new urine test developed by US scientists at the University of Texas is highly sensitive and can detect very small numbers of prions.
Professor James Ironside, head of the National CJD Research and Surveillance Unit based at the University of Edinburgh, said: “This is the first time that we have been able to detect prions in the urine of patients with variant CJD.
“It opens the door to the development of a screening tool for people infected with CJD who do not show any symptoms, which is of particular concern in the UK for securing the safety of our blood supply,” he said.
Professor Claudio Soto, from the University of Texas Medical School in Houston, said: “This could lead to the development of commercial technology for diagnosis as well as to determine the safety of donated blood and urinary products.”