Assessment of the risk factors related to bovine spongiform encephalopathy.

The Office International des Epizooties (OIE: World organisation for animal health) recommends that all OIE Member Countries determine the status of bovine spongiform encephalopathy (BSE) in their cattle populations by conducting a risk assessment and meeting certain BSE surveillance criteria. The OIE has identified and listed the factors and criteria for this in the International Animal Health Code. The factors to be assessed include the consumption of meat-and-bone meal (MBM) by cattle, the importation of cattle and MBM which are potentially infected or contaminated with the BSE agent, the livestock population structure, the rendering processes and the animal feeding practices. In this paper, the authors present an overview of these risk factors and criteria, detailing the relevant components of each. In the second part of this paper, the authors provide a risk assessment to demonstrate the application of the OIE BSE guidelines. This is a probabilistic risk assessment of the factors related to BSE for Canada which conforms to the OIE approach to import risk analysis. The steps include the hazard identification, release, exposure and consequence assessments and the risk estimation. A scenario tree for the release and exposure assessments was used to model the events emanating from the initiating failure event of importing cattle potentially infected with BSE. The consequence assessment describes the costs and losses associated with the introduction and establishment of BSE in other countries. The risk estimate, integrating the release, exposure and consequence assessments, indicates a negligible probability that BSE was introduced and established in Canada; nevertheless, the economic consequences would have been extreme.