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Bovine spongiform encephalopathy (BSE) (commonly known as mad cow disease), is an incurable and invariably fatal neurodegenerative disease of cattle. Symptoms include abnormal behavior, trouble walking, and weight loss. Later in the course of the disease the cow becomes unable to function normally. There is conflicting information around the time between infection and onset of symptoms. In 2002, the WHO suggested it to be approximately 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 had been reported globally. BSE is thought to be due to an infection by a misfolded protein, known as a prion. Cattle are believed to have been infected by being fed meat-and-bone meal (MBM) that contained either the remains of 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. It is a type of transmissible spongiform encephalopathy (TSE). 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 continental Europe, cattle over 30 months must be tested if they are intended for human food. In North America, tissue of concern, known as specified risk material, may not be added to animal feed or pet food. About four million cows were killed during the eradication programme in the UK. Four cases were reported globally in 2017, and the condition is considered to be nearly eradicated. In the United Kingdom, from 1986 to 2015, more than 184,000 cattle were diagnosed with the peak of new cases occurring in 1993. A few thousand additional cases have been reported in other regions of the world. It is believed that several million cattle with the condition likely entered the food supply during the outbreak.
