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Facts About BSE
Q: What is BSE?
A: Bovine spongiform encephalopathy (BSE) is a chronic, degenerative neurologic disease of cattle, commonly referred to as "mad cow disease." A member of the family of diseases known as transmissible spongiform encephalopathies (TSE), BSE has been diagnosed in native-born cattle in Austria, Belgium, Canada, Croatia, the Czech Republic, Denmark, Finland, France, Germany, Greece, Ireland, Israel, Italy, Japan, Liechtenstein, Luxembourg, the Netherlands, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom and the United States. More than 95% of cases identified have developed in the United Kingdom. Three cases of BSE have been confirmed in the United States. The first was in December 2003, but the cow was originally from Canada. The second case was confirmed in June 2005 and affected a native-born cow. The third was confirmed in March 2006. Countries with a single case are Finland, Greece, Israel and Sweden. In early 2005, BSE was confirmed as developing in a single goat that was slaughtered in 2002 in France.
Q: What causes BSE?
A: The theory accepted by most scientists is that BSE is caused by a prion (a self-replicating protein). The agent does not invoke a detectable immune response or inflammatory reaction in its host and is extremely resistant to sterilization.
Q: How is BSE transmitted?
A: Researchers believe that BSE is spread to cattle through feeding of contaminated meat and bone meal from scrapie-infected sheep or cattle with previously unidentified BSE. Tissues of particular risk include the brain, spinal cord, eyes, spleen, and certain other nervous tissues. BSE does not appear to be transmitted via contact between cattle or contact between cattle and other TSE-affected species.
Q: What clinical signs are associated with BSE?
A: In cattle, BSE causes progressive degeneration of the central nervous system. Clinical signs may include changes in temperament (apprehension, nervousness, unwillingness to move through doorways, belligerence), drooling, itching of the head, fine muscular tremors, moaning, rapid respiratory rate, slow heart rate, incoordination, abnormal postures, abnormal gait, decreased milk production, loss of body condition despite a normal appetite, and death. The incubation period ranges from 2 to 8 years and the health of affected animals typically deteriorates over a period of 2 weeks to 6 months. Most cattle affected are between 3 and 6 years old, although BSE has been diagnosed in younger and older cattle.
Q: How is BSE diagnosed and treated?
A: Unfortunately, there currently is no commercially available laboratory test to confirm BSE in a live animal. Bovine spongiform encephalopathy is most often diagnosed by examination of brain and spinal cord tissue after the animal's death. Special laboratory tests are used to confirm the presence of the abnormal prion protein in brain and spinal cord tissue. No treatment currently exists for cattle affected by BSE. The disease is uniformly fatal.
Q: How is BSE prevented?
A: Because the primary source of transmission of BSE has been shown to be proteins derived from BSE-infected cattle in feed, the Food and Drug Administration (FDA) has established regulations that prohibit the feeding of most mammalian proteins to ruminants in the United States. To prevent BSE from entering the United States, the United States Department of Agriculture's Animal and Plant Health Inspection Service (USDA-APHIS) has restricted importation of live ruminants and ruminant products (e.g., fetal bovine serum, meat-and-bone meal, bonemeal, bloodmeal, offal, fats, glands) from countries where BSE has been diagnosed. Because of concerns about cross-contamination of rendered products of nonruminant origin with the BSE agent, since 2000 the USDA has also prohibited all imports of rendered animal protein products, regardless of species, from BSE-affected countries.
Cattle presented for slaughter in the United States are evaluated by the Food Safety and Inspection Service (USDA-FSIS) for signs of neurologic disease. The carcasses of suspect cattle are condemned and are not used for human food. Central nervous system tissue from these animals is forwarded to laboratories for examination.
Q: What other animals get TSEs?
A: This disease family includes scrapie, affecting sheep and goats; transmissible mink encephalopathy; chronic wasting disease, affecting deer and elk; and, in humans, kuru, classic and variant Cruetzfeldt-Jakob disease, Gerstmann-Straussler syndrome, and fatal familial insomnia. A neurologic disease in exotic ruminants and exotic and household cats in the United Kingdom has been linked to BSE, and is suspected to be caused by eating feed contaminated with the BSE agent.
Q: Can BSE affect people?
A: Variant Cruetzfeldt-Jakob disease (vCJD) is a TSE with evidence of a causal link with BSE. It primarily affects young adults (median age at death is 28 years). Signs include early psychiatric and sensory abnormalities, eventually followed by difficulty walking, dementia, and involuntary muscle contractions. Median duration of illness is 14 months. Current thinking is that vCJD may be caused by ingestion of products contaminated with the BSE agent.
Variant Cruetzfeldt-Jakob disease (vCJD) is a TSE with evidence of a causal link with BSE. It primarily affects young adults (median age at death is 28 years). Signs include early psychiatric and sensory abnormalities, eventually followed by difficulty walking, dementia, and involuntary muscle contractions. Median duration of illness is 14 months. Current thinking is that vCJD may be caused by ingestion of products contaminated with the BSE agent.
Variant CJD is different from classic CJD, which is the TSE most often identified in humans. Classic CJD occurs worldwide at a rate of about 1 to 2 cases/1 million people. Mean age of onset is 65 years and median duration of illness is 4.5 months. Hereditary predisposition accounts for approximately 5 to 10% of cases, a sporadic form accounts for approximately 85 to 90% of cases, and a small number of cases are transmitted via contaminated surgical equipment, transplants (e.g., cornea, dura mater), or administration of natural human growth hormone.
BSE is an emerging disease and information is rapidly evolving. For the most current information, please consult the following Web sites:
http://www.avma.org/public_health/default.asp#bse
http://www.aphis.usda.gov/newsroom/hot_issues/bse.shtml
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