Multiple Reassortment between Pandemic (H1N1) 2009 and Endemic Influenza Viruses in Pigs, United States
Figure 2. Phylogenetic trees of pandemic reassortant swine influenza viruses compared with currently circulating swine influenza strains: A) hemagglutinin (H); B) neuraminidase (N); C) matrix genes. The trees were constructed by using the neighbor-joining method (Kimura 2-parameter) with 1,000 bootstrap replicates. Only bootstrap values >74 are shown. Swine reassortant strains characterized in this study are indicated with a closed circle. Boldface indicates pandemic segments. Greek letters indicate virus genogroups; α represents classical swine influenza virus and δ seasonal human-like swine influenza virus. TR indicates swine triple reassortant influenza virus. Scale bars indicate nucleotide substitutions per site.