Figure 4. Phylogenetic trees of canine influenza A(H3N2) virus (H3N2 CIV) sequences showing the initial emergence of the virus in southern China (green branches), its appearance in northern and eastern China (magenta branches) and South Korea (blue branches), and its introduction into the United States (red branches). A) Individual genome segment sequences. Red branch numbers indicate bootstrap proportion of US H3N2 CIV clade. Asterisks indicate polyphyletic clades containing US strains and most recent strains from South Korea. B) Concatenated segment phylogenies of all available complete nonreassortant H3N2 CIV genomes. Branch number indicates bootstrap proportions >75. All branch lengths are proportional to the number of nucleotide substitutions per site. All trees rooted by using sequences from the earliest isolated H3N2 CIV. Scale bars indicate nucleotide substitutions per site. HA, hemagglutinin; M1, matrix 1; NA, neuraminidase; NP, nucleocapsid protein; NS1, nonstructural 1; PA, polymerase acidic; PB1, polymerase basic 1; PB2, polymerase basic 2.