Figure 1. Evolutionary relationship of EV-D68 isolates.

(A) Phylogenetic tree of EV-D68 isolates used in this study. USA/MD/2009–23229 in clade A represents the pre-AFM isolate, while the isolates from clades B1, B2, B3, and D were circulating in peak AFM years. Optimal tree is shown and drawn to scale, with branch lengths in the same units (base substitutions per site) as the evolutionary distances used to construct the tree. Percentage next to the branches is replicate trees (1000 replicates) in which associated taxa clustered together via bootstrap test. Clade denoted in red. (B) Polyprotein diagram of EV-D68, with MD/09–23229 reference isolate represented on top in green. Isolates associated with AFM years are listed below in blue. Numbers within the protein schematic represent the number of amino acid mutations within that protein as compared to reference isolate.