Mad Cow Disease
(Bovine Spongiform Encephalopathy, or BSE)
Mad cow disease facts
*Mad cow disease facts medically edited by Charles Patrick Davis, MD, PhD
- Mad cow disease (bovine spongiform encephalopathy or BSE) is a progressive neurological disorder.
- Mad cow disease is caused by an infectious transmissible agent termed a prion.
- Mad cow disease was first noted in the 1970s and is thought to be related to another prion-caused disease termed Scrape that occurs in sheep; the first major outbreak of mad cow disease was in the United Kingdom, where more than 184,500 cases have been noted in cattle (2010 U.K. data found only 11 infected cattle).
- There is a relationship between mad cow disease and a human prion disease called variant Creutzfeldt-Jakob disease.
- In the United States, three cattle have been identified as having been infected with mad cow disease prions, while in Canada, 19 cases have been identified.
- Two strains of the mad cow disease prion have been identified, typical BSE strain and atypical BSE strain; the atypical strain may only occur spontaneously.
- Cattle-feed bans that prohibit feeding cattle any foods that contain cattle-derived or human-derived compounds may help reduce or eliminate transfer of typical BSE strain prions to other cattle.
- The prevalence of mad cow disease in the U.S. and Canada is considered to be very low (about
three to eight cases per million cattle in Canada and 0.167 cases per million in the United States); however, some researchers suggest these numbers are actually 18- to 48-fold higher.
Mad Cow Disease (BSE) History, Spread, and Link to vCJD
BSE (bovine spongiform encephalopathy) is a progressive neurological disorder
of cattle that results from 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.
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. Over the next 17 years, the annual numbers of BSE
cases has dropped sharply; 14,562 cases in 1995, 1,443 in 2000, 225 in 2005 and
11 cases in 2010. Cumulatively, through the end of 2010, more than 184,500 cases
of BSE had been confirmed in the United Kingdom alone in more than 35,000 herds.
There exists strong epidemiologic and laboratory evidence for a causal
association between a new human prion disease called
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.
Overview of BSE in North America
Through February 2011, BSE surveillance has identified 22 cases in North
America: 3 BSE cases in the U.S. and 19 in Canada. Of the 3 cases identified in
the United States, one was born in Canada; of the 19 cases identified in Canada,
one was imported from the United Kingdom (see figure above). Since March 2006,
each of the 15 cattle reported with BSE in North America were born in Canada and
identified through the Canadian BSE surveillance system.
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Mad Cow Disease - Experience
Question: Please describe your experience with mad cow disease (BSE).