Figure 3.

Phylogenetic associations of avian H7 viruses that have been reported to cause human infections

(A) Haemagglutinin gene. (B) Neuraminidase gene. (C) PB2 gene. The haemagglutinin, neuraminidase, and PB2 genes of the human isolates and the most closely related avian isolates, which are possible candidates as the gene source for reassortment, are shown. Only representative H7 isolates from human and the closely related isolates from avian species of preceding years are shown. The phylogenetic trees were constructed by the neighbour-joining method with bootstrap replication (1000 bootstraps) with MEGA 5.1. The neuraminidase gene sequence of 1996 influenza A H7N7 is not available in the public domain. Human strains are highlighted in red. Number of poultry culled is highlighted in blue. Scale bars show the estimated number of substitutions per 20 bases.