THE human form of mad cow disease could be identified through a urine test, paving the way for screening for people with no symptoms, according to researchers.

Variant Creutzfeldt-Jakob disease (CJD), linked to BSE in cattle, is caused by infectious proteins called prions and a team including staff at Edinburgh University have now developed a new technique to detect even small quantities of the agents.

Professor James Ironside, head of the national CJD research and surveillance unit at Edinburgh University, said: "This is the first time 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 for securing the safety of our blood supply."

Variant CJD can be t­ransmitted by eating beef infected with BSE or by receiving a blood transfusion from a person who carries the infectious prions. It can take a long time for symptoms to appear and people can have the disease for years before they are diagnosed.

A total of 229 people, including 177 from the UK, have died from variant CJD since it was first identified.