The most common example of spongiform encephalopathy (SE) is scrapie, a chronic wasting disease of the central nervous system (CNS) occurring in sheep. Prior to 1985, five other naturally occurring scrapie-like subacute, progressive, and always fatal infections were recognised: transmissible mink encephalopathy, wasting diseases of mule deer and elk; Creutzfeldt-Jakob disease (CJD); Kuru, and Gerstmann-Sträussler-Scheinker syndrome (GSSS). All SE's are slow developing infectious diseases. Because of strikingly similar degenerative lesions of the CNS, these disorders had been grouped together as SEs. Bovine spongiform encephalopathy (BSE) is the most recent addition to the group of SE diseases. In 1986 there were six cases of BSE in cattle. By 1999, BSE has claimed over 175,000 cattle in Great Britain.The cannibalistic practice of cattle to cattle recycling has resulted in the selection of a major new strain from a mixture of 20 "wild types" scrapie strains. This strain appears to be more virulent than unselected strains. The origin of BSE is believed to be the feeding of cattle with meat and bone meal prepared from sheep infected with scrapie.In my evidence to the BSE Inquiry, I had given account of the two main strains of scrapie known since 1961.Type I Scrapie: This type causes sheep to lose their wool and is the common type. Type II Scrapie: This is rarer form of scrapie. It shows up in sheep as trembling ataxia. Clinically it is the same in its major symptoms as BSE and a typical CJD cases. Prusiner, also now believes as he told a scientific meeting in Birmingham, in June 2000 that his colleague Mike Scott now believes that sheep carry two strains of the agent, the scrapie prion and the BSE prion while MAFF have not got a clue where BSE came from. However, Prof John Collinge believes Prusiner’s hypothesis is "flawed. There's no evidence (BSE) came from sheep, and if the prion that causes BSE is there, we can't find it." A few months later he published his work in National Academy of Science where he gave evidence that the BSE agent had infected all types of farm animals including hens. Paradoxically, cattle have selected the BSE agent from sheep infected with 'trotting' type II scrapie, which appears to be equally efficiently transmitted from one species to another by oral and intracerebral routes. In cattle there appears to be clear evidence of maternal transmission. Strain typing has implicated the BSE agent as the cause of spongiform encephalopathy in domestic cats, tigers, and in some exotic species of ruminants in zoos. Risk assessment of such circumstances is difficult, while consequences are grave. A single infected BSE cow entering the human food chain could potentially infect a large number of humans. It is wiser to take all steps possible to stop the spread of disease.