[[File:Aphis.usda.gov BSE 3.jpg|thumbnail|right|A cow unable to stand (downer) due to BSE.]]
Commonly known as “mad cow disease," '''Bovine bovine spongiform encephalopathy''' is a slowly progressive, incurable disease affecting the [[central nervous system]] of [[cattle]], first diagnosed in the United Kingdom in 1986. BSE belongs to a family of diseases known as the transmissible spongiform encephalopathies (TSEs). Consumption by cattle of animal feed containing TSE-contaminated ruminant protein [[meat and bone meal]] has been cited as one possible means of transmission. Scientific evidence supports a causal relationship between BSE outbreaks in Europe and more than 170 recent European cases of a human TSE, [[variant Creutzfeldt-Jakob Disease]] (vCJD). TSE animal diseases are found in the United States, including [[scrapie]] in sheep and goats and [[chronic wasting disease]] in deer and elk. Since 1989, USDA has prohibited the importation of live ruminants from countries where BSE is known to exist in native cattle. In 1997, the Food and Drug Administration (FDA) prohibited the use of most mammalian protein in ruminant feeds. It is possible for this disease to spread asymptomatically. BSE has an incubation period of 5 years, but cows are slaughtered at 18 months. This results in asymptomatic transmission to humans."<ref>[http://www.fsis.usda.gov/Help/glossary-B/index.asp]</ref>
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