Spatial and stochastic simulation to evaluate the impact of events and control measures ion the 1997-1998 classical swine fever epidemic in The Netherlands. I. Description of simulation model

The simulation model InterCSF was developed to simulate the Dutch Classical Swine Fever (CSF) epidemic of 1997-98 as closely as possible. InterCSF is a spatial, temporal and stochastic simulation model. The outcomes of the va rious replications give an estimate of the variation in size and duration o f possible CSF-epidemics. InterCSF simulates disease spread from an infecte d farm to other farms through three contact types (animals, vehicles, perso ns) and through local spread up to a specified distance. The main disease-c ontrol mechanisms that influence the disease spread in InterCSF are diagnos is of the infected farms, depopulation of infected farms, movement-control areas, tracing, and pre-emptive slaughter. InterCSF was developed using Int erSpread as the basis. InterSpread was developed for foot-and-mouth disease (FMD). This paper describes the process of modifying InterSpread into Inte rCSF This involved changing the assumptions and mechanisms for disease spre ad from FMD to CSF In addition, CSF-specific control measures based on the standard European Union (EU) regulations were included, as well as addition al control measures that were applied during the Dutch epidemic. To adapt I nterCSF as closely as possible to the Dutch 1997/98 epidemic, data from the real epidemic were analysed. Both disease spread and disease-control param eters were thus specifically based on the real epidemic. In general, InterS pread turned out to be a flexible tool that could be adapted to simulate an other disease with relative ease. The most difficult were the modifications necessary to mimic the real epidemic as closely as possible. The model was well able to simulate an epidemic with a similar pattern over time for num ber of detected farms as the real outbreak; but the absolute numbers were ( despite many relevant modifications) not exactly the same - but were within an acceptable range. Furthermore, the development of InterCSF provided the researchers with a better insight into the existing knowledge gaps. In par t II (see the final paper in this issue), InterCSF was used to compare vari ous control strategies as applied to this epidemic. (C) 1999 Elsevier Scien ce B.V. All rights reserved.