Antigenic and molecular characterization of avian influenza A(H9N2) viruses, Bangladesh

Abstract

Human infection with avian influenza A(H9N2) virus was identified in Bangladesh in 2011. Surveillance for influenza viruses in apparently healthy poultry in live-bird markets in Bangladesh during 2008-2011 showed that subtype H9N2 viruses are isolated year-round, whereas highly pathogenic subtype H5N1 viruses are co-isolated with subtype H9N2 primarily during the winter months. Phylogenetic analysis of the subtype H9N2 viruses showed that they are reassortants possessing 3 gene segments related to subtype H7N3; the remaining gene segments were from the subtype H9N2 G1 clade. We detected no reassortment with subtype H5N1 viruses. Serologic analyses of subtype H9N2 viruses from chickens revealed antigenic conservation, whereas analyses of viruses from quail showed antigenic drift. Molecular analysis showed that multiple mammalian-specific mutations have become fixed in the subtype H9N2 viruses, including changes in the hemagglutinin, matrix, and polymerase proteins. Our results indicate that these viruses could mutate to be transmissible from birds to mammals, including humans.

Keywords: Bangladesh; H5N1; H7N3; H9N2; avian influenza; avian influenza A(H9N2) viruses; influenza; molecular characterization; reassortants; respiratory infections; transmission; viruses; zoonoses.

Figure 1

Influenza virus surveillance in Bangladesh, November 2008–September 2012, showing the total number of avian influenza viruses isolated per month. A) Low pathogenicity subtype H9N2 viruses; B) highly pathogenic subtype H5N1 viruses.

Figure 2

Phylogenetic relationships of hemagglutinin genes of avian influenza (H9N2) viruses (boldface) isolated in Bangladesh. Full-length DNA sequencing, starting from the first codon, was used. The phylogenetic trees were generated by PhyML (30) within the maximum-likelihood framework. Numbers above the branches indicate bootstrap values; only values >60 are shown. Boldface italics indicate prototype subtype H9N2 viruses from the Ck/Bei and G1 clades. Scale bar indicates distance between sequence pairs.

Figure 3

Phylogenetic relationships of nonstructural protein genes of avian influenza (H9N2) viruses (boldface) isolated in Bangladesh. Full-length DNA sequencing, starting from the first codon, was used. The phylogenetic trees were generated by PhyML (30) within the maximum-likelihood framework. Numbers above the branches indicate bootstrap values; only values >60 are shown. Boldface italics indicate prototype subtype H9N2 viruses from the Ck/Bei and G1 clades. Scale bar indicates distance between sequence pairs.

Figure 4

Host range and pathogenicity determinants in avian influenza (H9N2) viruses isolated from different poultry species in Bangladesh during 2008–2011. Numbers in parentheses indicate number of viruses containing specific amino acid residues of the 44 virus isolates analyzed. Blue indicates the 11 genes that were assessed; red indicates the residues that are critical for influenza pathogenesis, enhanced replication in mammalian hosts, or those that are identical to residues present in human influenza viruses; green indicates unique substitutions in the viruses. HA, hemagglutinin; NA, neuraminidase; M, matrix; NS, nonstructural; NP, nucleoprotein; PA and PB, polymerase genes.