Na: number of pigs per group. Note that it is the initial number of pigs, i.e. the number at post infection day 0 that is stated. According to the experimental set-up, pigs were sequentially euthanized, i.e. 3 pigs from each group in week 1 and 2, respectively, thus in the 3rd week, only 4 pigs in each group were left and killed by termination of the study.