Here, the overall phylogeny (see Fig. 2 in the main text) is separated to show patterns of introduction and circulation within individual health zones for all lineages in the tree. Lineages are grouped by the health zone in which they circulated. Introductions are shown as circles at the beginning of each lineage. The color of the introduction circle indicates the donor health zone, and the x-axis position indicates the inferred timing of the introduction. While some lineages circulated in a health zone for long periods of time, most were short lived before moving into another health zone, as indicated by the relatively short branch lengths of many lineages. Visualization produced using BALTIC (github.com/evogytis/baltic/).