National Agricultural Biosecurity Center

BSE

Bovine Spongiform Encephalopathy (BSE), commonly known as mad cow disease, is a fatal neurodegenerative disease of cattle. Unlike many other kinds of infectious animal diseases, which are spread by microbes, BSE is a type of transmissible spongiform encephalopathy (TSE) that arises in animals via the spread of a specific type of protein referred to as a prion. Prions are self-replicating abnormal proteins and, in the brain of animals, these proteins cause native cellular prion protein to deform into the infectious state which ultimately results in the formation of dense plague fibers in the brain, degeneration of physical and mental abilities, and ultimately death. Scientist originally thought that BSE epizootic in cattle originated in sheep, in which the related prion disease scrapie is common. However, since the sheep and cattle TSEs are quite different, it is now thought more likely that BSE originated with a case of sporadic BSE in a single cow. The practice of feeding cattle rendered meat and bone meal, a high-protein substance obtained from the remnants of butchered animals (including cows and sheep) allowed for the accumulation of prions over many generations. The use of meat and bone meal as a protein supplement was widespread in Europe prior to 1990 and, as more animals became ill, more infectious tissue got into the feed until the number of cases reached epizootic proportions. These disease-causing prions can also be transmitted to humans and is thought to be the cause of variant Creutzfeldt-Jacob disease, a rare and fatal human brain-wasting disease.

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