Modelling pseudorabies virus infection supports eradicationA. Van Nesa, M.C.M. De Jongb and J.H.M. Verheijdena
a Department of Farm Animal Health, Utrecht University, 7 Yalelaan, 3584 CL Utrecht, The Netherlands
b Department of Immunology, Pathobiology & Epidemiology, Epidemiology, Statistics, and Modelling group, ID-DLO, Lelystad, The Netherlands
Abstract - Mathematical methods benefit the interpretation of results from experiments and observations under field conditions and thus enhance our understanding of the spread of infections within and between herds. Moreover, a mathematical model quantifies the impact of risk factors and thus determines whether or not the risk factor is a jeopardy for eradication. In this paper, we used a stochastic SIR model. The reproduction ratio between pigs can be calculated from this model. This reproduction ratio is defined as the mean number of pigs that is infected by one typical infectious pig. When , infection fades out and eradication will succeed, when an infection can spread. Hence, eradication is certain if is smaller than 1. However, when is larger than 1, eradication can still succeed when R between herds is below 1. Of course, when , eradication will be more rapid than when and . Measures to eradicate PRV aim to reduce or to below 1. The following conclusions can be drawn from our experiments, observations and modelling with pseudorabies virus (PRV): - Experimentally, it was shown that the number of pigs in a population (with a constant density of pigs per m 2) did not influence the reproduction ratio of PRV. There was, however, a significant difference in transmission between vaccinated not maternally immune SPF pigs and vaccinated maternally immune conventional pigs. Earlier experiments had already shown that transmission in maternally immune SPF pigs, which were vaccinated twice, was below one.
Corresponding author: A. Van Nes Tel.: (31) 30 2531248; fax: (31) 30 2521887;
© INRA, EDP Sciences 2000