Within-farm spread of classical swine fever virus--a blueprint for a stochastic simulation model

A stochastic simulation model to investigate the transmission of classical swine fever (CSF) virus within an infected farm is described. The model is structured according to the processes that occur within and between management groups (pig units or houses). It uses the individual pig as the unit of interest and estimates the number of animals in the states 'susceptible', 'infected', 'infectious', and 'removed' for each day of the disease incident. Probabilities are assigned to the transitions between states. The probability of a pig becoming infected is made dependent on the probability of contact between a susceptible and an infectious pig as well as the probability of transmission. The more pigs become infected in one unit, the more likely is subsequent spread to another management group on the farm. Ultimately, the probability that a shipment of pigs from the farm will include at least one infected pig can be estimated in order to identify high-risk movements during a CSF epidemic. The model results were compared with experimental data on CSF transmission within one pig unit (management group). It could be shown that the model was capable of reproducing the experimentally observed infection and mortality rates. To improve the input parameters and for further model validation, more experimental data and field data from CSF outbreaks are needed.