US researchers have identified the first biomarker for the human form of mad cow disease, a rare and fatal brain condition that typically kills people within one year of onset.

At present the only way to diagnose Creutzfeldt-Jakob disease is by studying brain tissue after a person dies. There is no cure.

If the biomarker can be used to develop a common test for the disease, it could help prevent its spread among healthy people and reduce misdiagnosis of potentially treatable dementia cases, the researchers said.

Scientists believe the disease can transfer from infected cattle to humans through tainted meat.

“Levels of the iron-transport protein transferrin are significantly decreased in the cerebrospinal fluid of patients well before the end stage of the disease, potentially allowing for earlier diagnosis,” said the study study led by Neena Singh and colleagues at Case Western Reserve University School of Medicine in Cleveland, Ohio.

The biomarker was 80 per cent accurate at distinguishing between mad cow and dementia.