Evaluation of Measures for the Control of Classical Swine Fever Using a Simulation Model
Abstract. A stochastic and temporal simulation model has been developed to simulate the spread of classical swine fever among herds within a certain area due to farm contacts and local spread. Due to spatial as well as on-farm level heterogeneities in pig production the model allows for the importing of individual farm data. The control measures movement restrictions within protection and surveillance zones, pre-emptive slaughter in proximity to detected farms and animal contact tracing with subsequent culling, applied additionally to stamping-out infected farms, were compared in relation to their effect on the size and the duration of possible epidemics. Additionally, the effects of varying efficiency in contact tracing were analysed.
An area with 2986 pig farms and a density of 1.34 farms per km² was generated stochastically for the analysis. When stamping-out infected herds was applied as a single measure, 532 farms became infected on average. The additional application of restriction zones led to a mean epidemic size of 8 infected farms. When all control measures were applied, 5 outbreaks occurred on average. However, the high number of herds depopulated in total curtailed the relative priority of this control strategy. Thus, the presented results point out the necessity to weigh up the advantages and disadvantages in the determination of the optimal control strategy. The simulation model is shown to be a good method to assess the possible consequences of different control measures. The control measures laid down in the EU Council Directive 2001/89/EC (stamping-out infected herds, contact tracing and implementation of restriction zones) seemed to be sufficient for the eradication of classical swine fever epidemics in a region of such farm density. A further reduction in the mean number of outbreaks could be observed when tracing efficiency increased and animal contacts were traced more quickly.