Bovine spongiform encephalopathy

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] The time between infection and onset of symptoms is generally 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]

Bovine spongiform encephalopathy
Other namesMad cow disease
A cow with BSE
SpecialtyNeurology, Veterinary medicine
SymptomsAbnormal behavior, trouble walking, weight loss, inability to move[1]
Complicationsvariant Creutzfeldt-Jakob disease (if BSE-infected beef is eaten by humans)
Usual onset4–5 years after exposure[2]
TypesClassic, atypical[1]
CausesA type of prion[3]
Risk factorsFeeding contaminated meat and bone meal to cattle
Diagnostic methodSuspected based on symptoms, confirmed by examination of the brain[1]
PreventionNot allowing older animals to enter the food supply, disallowing certain products in animal food[4]
PrognosisDeath within weeks to months[2]
Frequency4 cases (2017)[1]

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 (MBM) that contained either the remains of cattle who spontaneously developed the disease or scrapie-infected sheep products.[3][7] The outbreak increased throughout the United Kingdom 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 (TSE).[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, from 1986 to 2015, more than 184,000 cattle were diagnosed 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] It is believed that several million cattle with the condition likely entered the food supply during the outbreak.[1]