Mad Cow Disease (BSE)

What is Mad Cow Disease?

Mad Cow Disease or Bovine Spongiform Encephalopathy (BSE) is a transmissible, slowly progressive, degenerative, fatal disease affecting the central nervous system of cattle.¹ The disease was first diagnosed in 1986 in Great Britain.² The evidence suggests that BSE is spread through animal feed containing BSE-contaminated meat and bone meal as a protein source. There is no evidence that BSE spreads through contact between unrelated adult cattle or contact between cattle to other species.³ BSE is the bovine-specific form of a family of diseases known as transmissible spongiform encephalopathies (TSEs).³ The BSE agent causes no detectable immune or inflammatory response in the host and has yet to be observed microscopically. There is no test to detect the disease in live animals.³

What are TSEs and Related Diseases?

TSEs affect both humans and animals and are caused by⁴ an agent that is not yet completely characterized.^2,3,4 TSEs are largely believed to be caused by abnormally shaped proteins called prions⁵ that seem to spread inside the nervous system leading to cell death and lysis, causing the brain to have a sponge-like appearance.⁶ Other specific examples of TSEs include: scrapie, which affects sheep; chronic wasting disease (CWD), which affects deer and elk; and kuru, Creutzfeldt-Jakob disease (CJD), and the new variant Creutzfeldt-Jakob disease (vCJD), which affect humans.⁴

Current Methods to Detect BSE (TSE in Bovine)

Currently, there are two laboratory methods to confirm a diagnosis of BSE: (1) a microscopic examination of brain tissue to identify characteristic changes and (2) techniques that detect the presence of abnormal prion proteins in brain tissue; these techniques are immunohistochemistry, immunoblotting, and ELISA.³

The time to determination varies for the above tests, ranging from 4 to 5 hours for the ELISA technique to up to 5 days for the immunohistochemistry technique. The time to determination for the Abbott/Enfer TSE test is 3.5 hours.

How Does BSE Affect Humans?

The BSE disease in cattle is similar to the vCJD disease in humans. Both conditions are fatal brain diseases with long incubation periods of up to several years, and are caused by an unusual transmissible agent.⁷

In 1996, following outbreaks of BSE among British cattle, scientists found a possible link between BSE and vCJD.⁸ The disease, vCJD, may be acquired after consuming beef products from BSE-infected animals. There is strong scientific evidence (epidemiological and laboratory) that the agent that causes BSE in cattle is the agent that causes vCJD in people.¹

The disease, vCJD, which is generally found in younger persons, is very hard to diagnose until it has nearly run its course. In its early stages, the disease may manifest itself through neurological symptoms, but it is not until the latter stages that brain abnormalities detectable by x-ray or MRI can be seen.¹ As with BSE, there is no diagnostic test that can detect vCJD through a simple blood or plasma test.

Recent United States Update on BSE

On December 23, 2003, the USDA announced that a Holstein cow in the State of Washington had tested presumptively positive for BSE.⁹ On December 25, 2003, the diagnosis was confirmed by an international reference laboratory in England.⁷ According to the USDA, the beef supply is safe and there is an extremely low risk to human health due to consumption of BSE-contaminated beef.⁹ But the presence of mad cow disease in the U.S. raises a host of medical, regulatory, and safety questions, including whether BSE screening of cattle should be increased, research funding is adequate, and enough testing facilities exist.¹⁰

References

1. Consumer Questions and Answers About BSE (May 2003). Food and Drug Administration Web site. Available at: http://www.cfsan.fda.gov/%7Ecomm/bsefaq.html. Accessed: January 7, 2004.
2. Bovine Spongiform Encephalopathy (February 2002). USDA Web site. Available at: http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_ahbse.html. Accessed: January 7, 2004.
3. Bovine Spongiform Encephalopathy (BSE). USDA Web site. Available at: http://www.aphis.usda.gov/lpa/issues/bse/bse-overview.html. Accessed: January 7, 2004.
4. Transmissible Spongiform Encephalopathies (TSE) (July 2000). USDA Web site. Available at: http://www.aphis.usda.gov/lpa/pubs/ fsheet_faq_notice/fs_ahtse.html. Accessed: January 7, 2004.
5. Klass MR, Hodges S, Sayers R, et al. A test for transmissible spongiform encephalopathy. Am Biotechnol Lab 2002, 20(12)34–36.
6. Enfer TSE Kit 2.0 [Marketing Brochure A 92214]. Germany: ABBOTT; 2002.
7. BSE and CJD Information and Resources. CDC Web site. Available at: http://www.cdc.gov/ncidod/diseases/cjd/cjd.htm. Accessed: January 7, 2004
8. Federal Agencies Take Special Precautions to Keep “Mad Cow Disease” Out of the United States (August 2001). Health and Human Services Web site. Available at: http://www.hhs.gov/news/press/2001pres/01fsbse.html. Accessed: January 7, 2004
9. USDA News Release No. 0432.03. USDA Makes Preliminary Diagnosis of BSE.. USDA Web site. Available at: http://www.usda.gov/news/releases/ 2003/12/0432.htm. Accessed: January 7, 2004
10. Regalado A. U.S. research into prion diseases is limited. Wall Street Journal January 2, 2004.

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For more information

• United States Department of Agriculture (USDA)
• United States Meat Export Federation (USMEF)
• Food and Drug Administration (FDA)