A Closed Form Model for Assessing the Risk to Countries Importing Animals or Animal Products from Disease-Free Regions. S. Kaplan, Bayesian Systems, Inc., Rockville, MD; and R. M. McDowell, USDA-Animal and Plant Health Inspection Service, Riverdale, MD
Recent international sanitary and phytosanitary agreements (SPS) and concomitant changes in domestic regulations now permit importation of animals and animal products from disease-free regions within larger political/economic blocs not free of disease. If a disease outbreak occurs in free regions, disease-free countries importing such commodities risk the hazard of importing infected material until the outbreak is discovered and reported. Most prior risk analyses for similar import decisions have relied on using extensive scenario tree/fault tree modeling conventions. We report the development of a compact, parsimonious, closed-form model which utilizes an exponential model of disease spread between herds and within herds to estimate the volume of infected material imported per unit time. The model relies on eight parameters: rate of disease spread between herds, rate of spread within herds, time to detect outbreak, time to restore disease-free status once outbreak is detected, number of herds providing animals/product for export, quantity exported per unit time, and rate of disease occurrence in healthy population in disease-free area. The application of this model is demonstrated with a case study derived from a recent animal disease outbreak and subsequent efforts to export material from the surrounding disease-free areas.
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