Simulation studies of African horse sickness in Spain.

Factors affecting epidemics of African horse sickness in Spain were studied using a mathematical model. The model examined the likelihood of an epidemic after the introduction of the virus, and the effectiveness of vaccination strategies. Two host species (horses and donkeys) and one vector species (the biting midge Culicoides imicola) were included. A stratified random sampling method (Latin hypercube sampling) was used for sensitivity analysis of the likelihood of an epidemic. Systematic variation of vaccination parameters was used to consider alternative control strategies. In general, when an epidemic occurred most potential hosts became infected. The peak prevalence in C. imicola was low, and never exceeded 3%. The most significant factors in the likelihood of an epidemic were vector population size, the recovery rate in horses and the time of year when the virus was introduced. The lag between virus introduction and protection, the proportion of hosts vaccinated, and including donkeys in vaccination programmes where the factors that most strongly affected the success of different vaccination strategies. These factors should be priorities for empirical research, and should be considered in the design of control strategies in areas at risk of virus introduction.