Figure 2: Intercontinental migration events of swIAVs.

Circles represent the country of origin, based on the estimates summarized in the maximum clade credibility (MCC) tree, and are shaded accordingly. Lines represent the inferred time period of the intercontinental transmission, within a level of uncertainty, inferred from the estimated date of ancestral nodes on the MCC tree. Triangles represent clades resulting from the onward transmission of the introduced viruses, are shaded by the country of destination, and extend as far forward in time as the most recently sampled virus. Numbers of introduction (1–18) correspond to the clade numbers on the phylogenies (Fig. 3 and Supplementary Figs 1–7). The asterisks indicate that additional HA and NA swIAV sequence data ware used to estimate the timing of introduction 18. Countries/regions are abbreviated as follows: CHN=China (including Hong Kong SAR and Taiwan), THA=Thailand, VNM=Vietnam, KOR=South Korea, JPN=Japan, MEX=Mexico and EUR=Europe.