The identification of variant Creutzfeldt-Jakob disease (vCJD) in human strongly reinforced the perception of risks associated with the infectious agent involved in Bovine Spongiform Encephalopathy (BSE). The development of rapid tests for the diagnosis of BSE by the detection of the abnormal prion protein allowed a huge increase in surveillance of the cattle disease. This first revealed a higher prevalence of the infection than previously believed. However, food safety measures, mainly based on the ban of the use of meat and bone meal in ruminants and the elimination of specified risk materials from the food chain, already allowed significant progress in the control of the cattle disease, especially in the United Kingdom. Nevertheless, the diagnosis can still not be obtained in the live animal, while the disease only appears following a several years incubation period. Another major issue is the identification of the BSE agent when it has been transmitted to another species. This question not only arises in veterinary medicine, with the major question of a possible infection of small ruminants by the BSE agent, but also in human in which the existence of other forms of the disease linked to the BSE agent but possibly differing from Creutzfeldt-Jakob disease cannot be excluded.