Probability of acquiring infection at least once for Map-free farms as a function of the average number (over the nine years of data) of animals purchased per year. (A) Each point corresponds to a farm in the metapopulation, which purchased at least one animal during the nine-year simulation. The scenario with 1% of the farms initially infected, uniformly sampled, and with medium levels of within-herd prevalence is shown. The solid blue line corresponds to the prediction of the general linear model with the logarithm of the number of purchased animals (in-strength) as explanatory variable. (B) Each curve corresponds to a different proportion of farms initially infected (1% - solid lines and 10% - dotted lines), and their levels of within-herd prevalence (very low - black, low - green, medium - blue and high - red). Only scenarios with initially infected farms uniformly sampled are shown. Lines correspond to the prediction of the general linear model with the logarithm of the number of purchased animals (in-strength) as explanatory variable.