A protein widely distributed in tissues throughout the body, with the highest concentration in the brain, has been shown to be a specific marker in the spinal fluid of humans and animals infected with transmissible spongiform encephalopathies, scientists say. This discovery paves the way for the development of an improved test for the diagnosis of Creutzfeldt-Jakob disease in humans and encephalopathies in animals. The test could enable precise identification of disease in British cattle presently targeted for slaughter because of suspected infection with bovine spongiform encephalopathy, known as Mad Cow disease.