Bovine spongiform encephalopathy (more commonly "BSE" or "mad cow disease") is a fatal neurodegenerative disease of cattle. BSE is believed to be caused by prions and to be bovine counterpart of human prion disease Creutzfeldt-Jakob Disease and sheep prion disease scrapie. Eating meat from cattle with BSE is thought to have caused the new variant of Creutzfeldt-Jakob disease in about 90 cases in the U.K. and many more in France. All rodents injected with brain tissue obtained from cows with BSE develop a fatal neurological disorder in one or two years. It is possible to detect the abnormal prion protein in some but not all of these animals' brain tissues. Although there is substantial evidence for transmission of the disease by prions and various theories have developed about the absorbtion of prion proteins by intestinal cells, there is still no definite proof reliably showing that eating infected beef is really the cause of the new variant Creutzfeldt-Jakob disease. There is also some concern about those who work with (and therefore inhale) cattle bone meal, such as horticulturists who use it as fertilizer. The first BSE epidemic was recognized in the United Kingdom in 1986.
BSE is thought to have arisen from cattle fed with a high-protein diet, obtained from remnants of butchered animals and modified by some new methods developed in the early 1980s. This practice allows the accumulation of prions over many generations, and is now disallowed by modern cattle farming practices. To date (2001) there has not been a case of BSE in the United States, nor a case of new-variant Creutzfeldt-Jakob Disease except among those who have travelled to Europe.