London - Scientists yesterday said they are a step closer to developing a diagnostic test for mad cow disease and its human equivalent. Researchers at Prionics AG, based at the University of Zurich, said in a report in the science journal, Nature, that they have discovered an antibody for the mutated prion brain protein that causes the brain-wasting illness. Until now, cases of bovine spongiform encephalopathy (BSE) in animals or Creutzfeldt-Jakob Disease (CJD) in humans could only be confirmed by examining brain tissue from victims.