Analysis of BVDV outbreaks at herd scale. A Re-infection probability vs. infection probability. Each point represents one herd. The red line is the smoothed non-parametric regression line. B Number of new infections per herd-run, function of the average number of animals purchased per herd-year. The circle size is proportional to the number of neighbours and the colour is related to the proportion of new infections due to a specific transmission route (from red when only due to neighbourhood contacts to blue when only due to animal trade). Analyses were based on 100 runs.