Bovine spongiform encephalopathy

Bovine spongiform encephalopathy
Other names	Mad cow disease
A cow with BSE
Specialty	Neurology, veterinary medicine
Symptoms	Abnormal behavior, trouble walking, weight loss, inability to move[1]
Complications	Variant Creutzfeldt-Jakob disease (if BSE-infected beef is eaten by humans)
Usual onset	4–5 years after exposure[2]
Types	Classic, atypical[1]
Causes	A type of prion[3]
Risk factors	Feeding contaminated meat and bone meal to cattle
Diagnostic method	Suspected based on symptoms, confirmed by examination of the brain[1]
Prevention	Not allowing sick or older animals to enter the food supply, disallowing certain products in animal food[4]
Treatment	None
Prognosis	Death within weeks to months[2]
Frequency	4 reported cases (2017)[1]

Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is an incurable and invariably fatal neurodegenerative disease of cattle.^[2] Symptoms include abnormal behavior, trouble walking, and weight loss.^[1] Later in the course of the disease, the cow becomes unable to function normally.^[1] There is conflicting information about the time between infection and onset of symptoms. In 2002, the World Health Organization suggested it to be approximately four to five years.^[2] Time from onset of symptoms to death is generally weeks to months.^[2] Spread to humans is believed to result in variant Creutzfeldt–Jakob disease (vCJD).^[3] As of 2018, a total of 231 cases of vCJD had been reported globally.^[5]

BSE is thought to be due to an infection by a misfolded protein, known as a prion.^[3][6] Cattle are believed to have been infected by being fed meat-and-bone meal that contained either the remains of cattle who spontaneously developed the disease or scrapie-infected sheep products.^[3][7] The United Kingdom was afflicted with an outbreak of BSE and vCJD in the 1980s and 1990s. The outbreak increased throughout the UK due to the practice of feeding meat-and-bone meal to young calves of dairy cows.^[3][8] Cases are suspected based on symptoms and confirmed by examination of the brain.^[1] Cases are classified as classic or atypical, with the latter divided into H- and L types.^[1] It is a type of transmissible spongiform encephalopathy.^[9]

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.^[4] In continental Europe, cattle over 30 months must be tested if they are intended for human food.^[4] In North America, tissue of concern, known as specified risk material, may not be added to animal feed or pet food.^[10] About four million cows were killed during the eradication programme in the UK.^[11]

Four cases were reported globally in 2017, and the condition is considered to be nearly eradicated.^[1] In the United Kingdom, more than 184,000 cattle were diagnosed from 1986 to 2015, with the peak of new cases occurring in 1993.^[3] A few thousand additional cases have been reported in other regions of the world.^[1] In addition, it is believed that several million cattle with the condition likely entered the food supply during the outbreak.^[1]