Figure 2

Subtyping of influenza A virus by surface protein genes of influenza A virus

(A) Phylogenetic tree of the haemagglutinin gene. (B) Phylogenetic tree of the neuraminidase gene. Subtypes in bold colour represent those that have been found in human beings. Subtypes in blue have caused human seasonal or pandemic influenza. Subtypes in red are avian-origin influenza. Subtypes in green have caused both human seasonal and pandemic influenza or avian-origin influenza. Number in parenthesis shows number of human real-time-PCR or culture-confirmed avian influenza infections reported, but not including the 2013 influenza A H7N9 cases. The sequences were retrieved from the NCBI database and the phylogenetic trees were constructed by the neighbour-joining method with bootstrap replication (1000 bootstraps) with MEGA 5.1. Numbers at nodes show levels of bootstrap support calculated from 1000 trees. Scale bars show the estimated number of substitutions per ten bases.