Mad cow disease (BSE) and the similar human new variant Creutzfeldt-Jakob-Disease (nvCJD) are fatal diseases in which the brain tissue breaks down. It is believed that rogue proteins called prions are to blame. These are not microbes in the usual sense because they are not alive, but the illness they cause can be transmitted from one animal to another. It seems that people eating meat from cattle suffering from BSE can sometimes develop a new and frightening form of CJD years later. The beef in these cases was probably contaminated with affected brain and spinal cord tissue. The government has introduced measures in slaughterhouses and butchers to minimise the risk to beef consumers. The diseases have caused an economic crisis in the meat industry world-wide. No-one knows what the real threat from BSE is to people or how many cases of CJD there will be in the future. Extensive research into the subject is underway, but it is a slow and difficult process as prions cannot be cultured in the laboratory like bacteria or fungi.