(p. 228). That analysis allowed the development of a matrix to depict five overall risk designations: very high, high, moderate, low, and very low. For example, deli meats are considered very high risk because they were in the high cluster for both per-serving and per-annum consumption.

BOVINE SPONGIFORM ENCEPHALOPATHY

Bovine spongiform encephalopathy (BSE), commonly referred to as mad cow disease, is a chronic degenerative disease that affects the central nervous system of cattle. BSE is one of a number of transmissible spongiform encephalopathies that are caused by infectious agents associated with an abnormally folded protein known as a prion (IOM, 2004). In cattle, the infectious agent is transmitted through ingestion of contaminated feed. In humans, exposure to beef products that are infected with BSE can lead to Creutzfeldt-Jakob disease (CJD), a fatal neurodegenerative disease (IOM, 2004). Because there are no vaccines against or treatments for BSE or CJD and because it is extremely difficult to destroy the infectious agent, preventing the spread of BSE among cattle and preventing cattle infected with BSE from entering the human food supply are key control mechanisms. The potential human health consequences from CJD are severe, and the costs of an outbreak are high. For example, hundreds of thousands of infected animals had to be destroyed, and trade restrictions were instituted by other countries, following an outbreak of BSE in Britain in 1985 (IOM, 2004).

In 1998 the U.S. Department of Agriculture (USDA) requested that the Harvard Center for Risk Analysis (HCRA) evaluate measures to control the spread of BSE among animals and from animals to humans. In response, in 2003 the HCRA developed a model to simulate the consequences of introducing BSE into the United States by various means (Cohen et al., 2003a,b). USDA and the public provided comments on the assessment, and HCRA published an updated assessment in 2005 (Cohen and Gray, 2005), and the results of additional simulations were published in 2006 (Cohen, 2006). The assessment demonstrates how, when faced with uncertainty about the best regulatory option, the effects of different management options can be modeled to inform the decision-making process.

Assessment of BSE Infection Risks

To assess the risks to cattle and to humans from the introduction of BSE in the United States, HCRA designed a model that could predict “the number of newly infected animals that would result from introduction of BSE, the time course of the disease following its introduction, and the potential for human exposure to infectious tissues” (Cohen et al., 2003b, p. vii). The model also incorporated “key processes and procedures that



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