Phylogenetic analysis of influenza A viruses of H9 haemagglutinin subtype

A 380 nucleotide region (bases 613 to 992) of the HA1 part of the haemagglu tinin (H) gene was obtained for 35 influenza viruses of H9 subtype isolated from around the world over the past 33 years. These were analyzed phylogen etically and compared with sequences from 19 H9 subtype viruses available i n the Genbank database. These viruses do not show such clear geographical l ineages as other subtypes (i.e. H5 or H7) and there is a high degree of var iation at the cleavage site of the haemagglutinin. Genetically distinct lin eages of H9 viruses have circulated contemporaneously in different location s. Thus, it is likely that the numerous infections of poultry and other bir ds with H9 subtype influenza viruses during the 1990s originate from separa te introductions from feral birds. The observed heterogeneity of these viru ses may reflect the gene pool for H9 viruses, which is maintained in shoreb irds and gulls (Charadriiformes).