Fig. 1.

Phylogenetic subtrees of all eight segments of the novel influenza A/H1N1 viruses. The phylogenetic trees were constructed with MEGA 4.0 by using the NJ method, and the reliability of the tree was evaluated by the bootstrap method with 1,000 replications. Only bootstrap values of >80 are shown at the corresponding nodes. The triple-reassortant swine influenza A/H1N1 virus lineages that originated from the reassortment between avian, human, and swine lineages are circulating in swine, even occasionally in human, in North America. The GenBank accession numbers of the sequences used in this figure are provided in Table S1