FIG. 1.

Phylogenetic relationships of the H5 hemagglutinin genes. The tree includes avian influenza isolates collected during the 2003 and 2004 outbreak in Asia and selected ancestors dating back to 1996 (see Materials and Methods for database accession numbers). The viruses evaluated in this study are in boldface type. HA clades are indicated by curved brackets. Phylogenetic trees were inferred from nucleotide sequences by the neighbor-joining method with A/Chicken/Scotland/56 genes as the outgroup (not shown; the branch position is indicated by the arrow). Bootstrap analysis values of ≥90% are shown above the branches. The scale bar indicates the number of nucleotide (nt) changes per unit length of the horizontal branches.