Phylogenetic tree based on nucleotide sequences of the H5 HA gene. The tree was generated by the maximum parsimony method with the PAUP4.0b10 program with bootstrap replication (100 bootstraps) and a heuristic search method. The tree is rooted to A/chicken/Scotland/59. Previously identified highly pathogenic viruses are indicated as HP in parentheses. *, Ruddy Turnstone/NJ/2242/00 virus belongs to the recent live-bird market phylogenetic lineage, but the virus was not recovered from live-bird market. Abbreviations: CK, chicken; DK, duck; TK, turkey. Standard two-letter abbreviations are used for states in the United States.