Transmissible Spongiform Encephalopathies (TSEs), Including "Mad Cow Disease": Public Health and Scientific Issues

Publication Date: March 2004

Publisher: Library of Congress. Congressional Research Service

Author(s):

Research Area: Health

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Abstract:

On December 23, 2003, the U.S. Secretary of Agriculture announced that a cow in Washington state had tested positive for bovine spongiform encephalopathy (BSE, or Mad Cow disease), representing the first domestic case. The Secretary announced expanded protections against BSE on December 30, 2003. On January 26, 2004, the U.S. Secretary of Health and Human Services announced additional safety measures for products regulated by the U.S. Food and Drug Administration (FDA) to protect public health. Both have stressed that the human health impact of finding one BSE positive cow is believed to be minimal.

BSE is a member of a group of diseases called Transmissible Spongiform Encephalopathies (TSEs). Although the predominant theory is that TSEs are caused by prions or proteinaceous infectious particles (a novel disease mechanism first described in the 1980s), some scientists believe a virus may eventually be identified as the infectious agent. While some TSEs, such as scrapie in sheep, have been known for over 200 years, others, including BSE, appear to have emerged quite recently. Some TSEs seem to affect only one species and others, like BSE, appear to have jumped the "species barrier" to infect more than one species. This event has transformed prion diseases from a rare and esoteric area of research to a matter of significant public health concern. BSE is believed to have been transmitted to people who ate contaminated beef, leading to the identification in 1996 of a new human disease, variant Creutzfeld-Jakob disease (vCJD), in the United Kingdom.

As attention has focused on the finding of BSE in the United States, government control efforts have been scrutinized. Some have argued that prevention programs, begun in 1988 and strengthened at points since then, are robust, and that the finding of a BSE-positive cow represents an isolated case and a negligible health risk to humans. Others believe that shortfalls in government prevention efforts are serious, and that BSE may be entrenched in the United States, albeit at low levels. The spectrum of opinions about the public health risk from BSE underscores the myriad uncertainties surrounding prion diseases, and especially their modes of transmission, and detection.

This report examines known and purported human health risks from BSE and related diseases, the status of efforts to detect and prevent these diseases in humans, and the scientific basis of these efforts. For a discussion of BSE prevention efforts in the agricultural sector (including FDA measures to assure the safety of animal feed, and USDA measures to assure the safety of beef), refer to CRS Issue Brief IB10127, Mad Cow Disease: Agricultural Issues for Congress, by Geoffrey S. Becker, and CRS Report RL32199, Bovine Spongiform Encephalopathy (BSE, or 'Mad Cow Disease'): Current and Proposed Safeguards, by Sarah A. Lister and Geoffrey S. Becker.

This report will be updated as circumstances warrant.