Fig. 1

The United States as the immediate origin of HCV1a spread to Europe and Italy. The branches in the HCV1a maximum clade credibility (MCC) tree constructed from the complete dataset are colored according to sampling country with strains grouped into four locations (see legend). All but five Q80K strains are found in the same clade, which is highlighted in grey. We refer to Fig. 3 for further details on the Q80K history. Mixing of strains among the four locations can be observed in the entire tree. HCV entered Italy via the US and continental migration in the two major clades of HCV1a variability (Clade I and II) as well as in the Q80K clade. Posterior root node support is visualized in a selection of deeper nodes. a: entire dataset. b: MCC tree estimated from subsample 1 (see Methods). c: MCC tree estimated from subsample 2. d: MCC tree estimated from subsample 3