Phylogenetic trees for the HA (A), NA (B), and PA (C) genes of the H5N1 influenza A viruses analyzed.

<p>The trees were generated by using CLUSTALx1.83 and MEGA4.0 software by the NJ method (Bootstrap test:1000 replicates, seed = 64238 ) on the basis of the following gene sequences: nucleotides 29–1,695 (1,667 bp) of HA, 21–1,358 (1,338 bp) of NA, and 25–2,163 (2,139 bp) of PA. The length of each pair of branches represents the distance between the sequence pairs, and the units at the bottom of the tree indicate the number of substitution events. The 15 H5N1 isolates from Vietnam are marked in bold italic. Abbreviations: CK, chicken; DK, duck; MDK, Muscovy duck; QL, quail; GS, goose; GD, Guangdong; GX, Guangxi; HK, Hong Kong; VN, Vietnam; SX, Shanxi.