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] There is conflicting information about the time between infection and onset of symptoms. In 2002, the World Health Organization (WHO) 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]
"Mad cow" redirects here. For other uses, see Mad cow (disambiguation).Bovine spongiform encephalopathy
Mad cow disease
Abnormal behavior, trouble walking, weight loss, inability to move[1]
Variant Creutzfeldt-Jakob disease (if BSE-infected beef is eaten by humans)
4–5 years after exposure[2]
Classic, atypical[1]
Feeding contaminated meat and bone meal to cattle
Suspected based on symptoms, confirmed by examination of the brain[1]
Not allowing sick or older animals to enter the food supply, disallowing certain products in animal food[4]
None
Death within weeks to months[2]
4 reported 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 United Kingdom (UK) 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 (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] In addition, it is believed that several million cattle with the condition likely entered the food supply during the outbreak.[1]
Pathogenesis[edit]
The pathogenesis of BSE is not well understood or documented like other diseases of this nature. Even though BSE is a disease that results in neurological defects, its pathogenesis occurs in areas that reside outside of the nervous system.[21] There was a strong deposition of PrPSc initially located in the ileal Peyer's patches of the small intestine.[22] The lymphatic system has been identified in the pathogenesis of scrapie. It has not, however, been determined to be an essential part of the pathogenesis of BSE. The Ileal Peyer's patches have been the only organ from this system that has been found to play a major role in the pathogenesis.[21] Infectivity of the Ileal Peyer's patches has been observed as early as four months after inoculation.[22] PrPSc accumulation was found to occur mostly in tangible body macrophages of the Ileal Peyer's patches. Tangible body macrophages involved in PrPSc clearance are thought to play a role in PrPSc accumulation in the Peyer's patches. Accumulation of PrPSc was also found in follicular dendritic cells; however, it was of a lesser degree.[23] Six months after inoculation, there was no infectivity in any tissues, only that of the ileum. This led researchers to believe that the disease agent replicates here. In naturally confirmed cases, there have been no reports of infectivity in the Ileal Peyer's patches. Generally, in clinical experiments, high doses of the disease are administered. In natural cases, it was hypothesized that low doses of the agent were present, and therefore, infectivity could not be observed.[24]
Prevention[edit]
A ban on feeding meat and bone meal to cattle has resulted in a strong reduction in cases in countries where the disease has been present. In disease-free countries, control relies on import control, feeding regulations, and surveillance measures.[25]
In UK and US slaughterhouses, the brain, spinal cord, trigeminal ganglia, intestines, eyes, and tonsils from cattle are classified as specified risk materials, and must be disposed of appropriately.[25]
An enhanced BSE-related feed ban was enacted in both the United States (2009) and Canada (2007) to help improve prevention and elimination of BSE.[30]
History[edit]
Different hypotheses exist for the origin of BSE in cattle. One hypothesis suggests it may have jumped species from the scrapie disease in sheep, and another hypothesis suggests that it evolved from a rare spontaneous form of "mad cow disease" that has been seen occasionally in cattle for many centuries.[89][90] In the fifth century BC, Hippocrates described a similar illness in cattle and sheep, which he believed also occurred in humans.[91] Publius Flavius Vegetius Renatus recorded cases of a disease with similar characteristics in the fourth and fifth centuries AD.[92]
In more recent UK history, the official BSE inquiry (published 2000) suggested that the outbreak there "probably arose from a single point source in the southwest of England in the 1970s".[7]
The most recent case in the UK was in May 2024, on a farm in Ayrshire, Scotland.[93]