Developing stochastic epidemiological models to quantify the dynamics of infectious diseases in domestic livestock

A stochastic model describing disease transmission dynamics for a micropara sitic infection in a structured domestic animal population is developed and applied to hypothetical epidemics on a pig farm. Rational decision making regarding appropriate control strategies for infectious diseases in domesti c livestock requires an understanding of the disease dynamics and risk prof iles for different groups of animals. This is best achieved by means of sto chastic epidemic models. Methodologies are presented for 1) estimating the probability of an epidemic, given the presence of an infected animal, wheth er this epidemic is major (requires intervention) or minor (dies out withou t intervention), and how the location of the infected animal on the farm in fluences the epidemic probabilities; 2) estimating the basic reproductive r atio, R-0 (i.e., the expected number of secondary cases on the introduction of a single infected animal) and the variability of the estimate of this p arameter; and 3) estimating the total proportion of animals infected during an epidemic and the total proportion infected at any point in time. The mo del can be used for assessing impact of altering farm structure on disease dynamics, as well as disease control strategies, including altering farm st ructure, vaccination, culling, and genetic selection.