<Tr> <Th> Frequency </Th> <Td> 4 cases (2017) </Td> </Tr> <P> Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a neurodegenerative disease of cattle . Symptoms include abnormal behavior, trouble walking, and weight loss . Later in the course the cow becomes unable to move . The time between infection and onset of symptoms is generally four to five years . Time from onset of symptoms to death is generally weeks to months . Spread to humans is believed to result in variant Creutzfeldt--Jakob disease (vCJD). As of 2018 a total of 231 cases of vCJD have been reported globally . </P> <P> BSE is due to an infection by a misfolded protein, known as a prion . Cattle are believed to have been infected by being feed meat - and - bone meal (MBM) that contained the remains of other cattle who spontaneously developed the disease or scrapie - infected sheep products . The outbreak increased throughout the United Kingdom due to the practice of feeding meat - and - bone meal to young calves of dairy cows . Cases are suspected based on symptoms and confirmed by examination of the brain . Cases are classified as classic or atypical, with the latter divided into H - and L types . </P> <P> Efforts to prevent the disease in the UK include not allowing any animal older than 30 months to enter either the human food or animal feed supply . In Europe all cattle over 30 month must be tested if they will become human food . In North America tissue of concern, known as specified risk material, may not be added to animal feed or pet food . About 4.4 million cows were killed during the eradication program in the UK . </P>

Where did the mad cow disease come from