Sensitivity analysis of a stochastic simulation model for foot and mouth disease

A spatial and temporal Monte-Carlo simulation model was developed to analyse the epidemiology and control of foot and mouth disease (FMD). Animal, people and vehicle contacts as well as airborne and local spread represented the FMD virus transmission between farms housing cattle, pigs or sheep. Contacts were explicitly modelled by routes, airborne transmission by the Gaussian Dispersion model and local spread by distance dependent transmission probabilities. Control measures were implemented according to the EU Directive (2003/85/EG). A sensitivity analysis with a two-level fractional factorial design was used to examine the robustness of the simulation model to extreme input values. The influence of eleven input parameters and interactions between them were estimated: ability of airborne spread, duration of the incubation period, time from infection until infectivity, time from onset of clinical signs until diagnosis, farm density, type of index case, number of farms visited per route, visiting interval, type of the animal sales, control strategy, and delay until start of control strategies. The considered parameters as well as certain two-factor interactions between them showed a significant impact on the epidemic duration and the number of infected and culled farms. Particularly, the parameter airborne spread, farm density, number of farms visited per route and control strategy influenced the course of the epidemic. The consideration of airborne spread as well as the implementation of contacts between farms with routes allowed a detailed analysis of these transmission paths.