Figure 2.

The panorama phylogenetic tree of type A influenza virus based on the viral PB1 gene sequences. The tree could be divided into at least 8 lineages, and some lineage could be further divided into some sublineages. The distribution of host, isolation time, isolation regions and subtypes of the majority within each sublineages were shown near to the relevant designations. The current A(H1N1) viruses were within the sublineage S2.1.10 (at the top). Bootstrap values were given at relevant nodes.