Bovine spongiform encephalopathy

A transmissible encephalopathy of cattle characterized by a spongiform structure of the brain tissue, and associated with abnormal prion proteins in the brain.

BSE - mad cow disease

Mad cow disease

• BSE is commonly known as mad cow disease
• BSE is a slowly progressive, incurable disease affecting the central nervous system of cattle, first diagnosed in the United Kingdom in 1986.
• BSE belongs to a family of diseases known as the transmissible spongiform encephalopathies (TSEs).
• Consumption by cattle of animal feed containing TSE-contaminated ruminant protein has been cited as one possible means of transmission. Scientific evidence supports a causal relationship between BSE outbreaks in Europe and more than 120 recent European cases of a human TSE, variant Creutzfeldt-Jakob Disease (vCJD).
• TSE animal diseases are found in the United States, including scrapie in sheep and goats and chronic wasting disease in deer and elk.
• Since 1989, USDA has prohibited the importation of live ruminants from countries where BSE is known to exist in native cattle.
• In 1997, the Food and Drug Administration (FDA) prohibited the use of most mammalian protein in ruminant feeds.

Histology of BSE

Cause

• BSE is caused by infection by an unusual transmissible agent called a prion.
• The nature of the transmissible agent is not well understood.
• Currently, the most accepted theory is that the agent is a modified form of a normal protein known as prion protein.
• For reasons that are not yet understood, the normal prion protein changes into a pathogenic (harmful) form that then damages the central nervous system of cattle.

Possible link between scrapie and BSE

• Research indicates that the first probable infections of BSE in cows occurred during the 1970’s with two cases of BSE being identified in 1986. * BSE possibly originated as a result of feeding cattle meat-and-bone meal that contained BSE-infected products from a spontaneously occurring case of BSE or scrapie-infected sheep products.
• Scrapie is a prion disease of sheep.
• There is strong evidence and general agreement that the outbreak was then amplified and spread throughout the United Kingdom cattle industry by feeding rendered, prion-infected, bovine meat-and-bone meal to young calves.
• The BSE epizootic in the United Kingdom peaked in January 1993 at almost 1,000 new cases per week.
• Since then, the annual numbers of BSE cases in the United Kingdom have dropped sharply.

Mad cow

Link between BSE and vCJD

• Strong epidemiologic and laboratory evidence exists for a causal association between a new human prion disease called [[variant Creutzfeldt-Jakob disease[[ (vCJD) that was first reported from the United Kingdom in 1996 and the BSE outbreak in cattle.
• The interval between the most likely period for the initial extended exposure of the population to potentially BSE-contaminated food (1984-1986) and the onset of initial variant CJD cases (1994-1996) is consistent with known incubation periods for the human forms of prion disease.

Prevention

• Because the use of ruminant tissue in ruminant feed was probably a necessary factor responsible for the BSE outbreak in the United Kingdom and because of the current evidence for possible transmission of BSE to humans, the U.S. Food and Drug Administration instituted a ruminant feed ban in June 1997 that became fully effective as of October 1997.
• As of October 26, 2009, a regulation issued by FDA in April 2009 came into effect establishing an enhanced BSE-related feed ban in the U.S.
• This enhanced feed ban will further harmonize BSE feed control measures in the U.S. with those in Canada (see below).
• In addition, FDA continues to enforce its important 1997 mammalian-to-ruminant feed ban through its BSE inspection and BSE feed testing programs.
• As of July 12, 2007, an enhanced BSE-related feed ban came into effect in Canada and similar bans are also in place in many countries.

Bovine spongiform encephalopathy Resources
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