Sequence Analysis of the PB1 Polymerase Genes of H3 Subtype Duck Influenza Viruses

Objective Aquatic birds are the natural reservoir of avian influenza viruses.There exists a close relationship between the avian and human influenza.There are frequent epidemics of H3 subtype influenza virus among humans and the surveillance show that the carrier rate of H3 subtype influenza virus in aquatic birds is comparatively high.Methods To illustrate the relationship of H3 subtype influenza virus with other subtypes,we carried out the sequence analysis of PB1 polymerase genes of three H3N8 subtype duck influenza virus strains isolated from the live bird markets.Results The results showed that the nucleotide homologies of PB1 gene among the 3 strains of duck virus isolates were 99.9%,and those with H9N2 subtype virus(DK/ST/2143/00) were 96.31%～96.44%,but those with H3N8 virus(Mal/Alberta/279/98) were 88.65%～88.79%.The phylogenetic analysis showed that the PB1 genes of these three isolates fell into the same cluster and belonged to the cluster of A/duck/Hong Kong/Y439-like H9N2 subtype avian influenza viruses,which demonstrated that the gene segments of the three H3N8 subtype viruses reassorted with H9N2 virus strains.Conclussion The present findings suggest that we should pay great attention to the reassortment among different subtypes avian influenza viruses in natural host and the new characteristics of the reassortants,such as the pathogenicity of H3N8 subtype duck influenza viruses to chickens.