Phylogenetic analysis of H7 haemagglutinin subtype influenza A viruses

A 945 nucleotide region (bases 76-1020) of the HA1 part of the HA gene was obtained for 31 influenza viruses of H7 subtype isolated primarily from Eur ope, Asia and Australia over the last 20 years. These were analysed phyloge netically and compared with sequences of the same region from 23 H7 subtype viruses available in Genbank. The overall results showed two geographicall y distinct lineages of North American and Eurasian viruses with major subli neages of Australian, historical European and equine viruses. Genetically r elated sublineages and clades within these major groups appeared to reflect geographical and temporal parameters rather than being defined by host avi an species. Viruses of high and low virulence shared the same phylogenetic branches, supporting the theory that virulent viruses are not maintained as a separate entity in waterfowl.