H9N2 influenza viruses possessing H5N1-like internal genomes continue to circulate in poultry in southeastern China

Abstract

The transmission of H9N2 influenza viruses to humans and the realization that the A/Hong Kong/156/97-like (H5N1) (abbreviated HK/156/97) genome complex may be present in H9N2 viruses in southeastern China necessitated a study of the distribution and characterization of H9N2 viruses in poultry in the Hong Kong SAR in 1999. Serological studies indicated that H9N2 influenza viruses had infected a high proportion of chickens and other land-based birds (pigeon, pheasant, quail, guinea fowl, and chukka) from southeastern China. Two lineages of H9N2 influenza viruses present in the live-poultry markets were represented by A/Quail/Hong Kong/G1/97 (Qa/HK/G1/97)-like and A/Duck/Hong Kong/Y280/97 (Dk/HK/Y280/97)-like viruses. Up to 16% of cages of quail in the poultry markets contained Qa/HK/G1/97-like viruses, while about 5% of cages of other land-based birds were infected with Dk/HK/Y280/97-like viruses. No reassortant between the two H9N2 virus lineages was detected despite their cocirculation in the poultry markets. Reassortant viruses represented by A/Chicken/Hong Kong/G9/97 (H9N2) were the major H9N2 influenza viruses circulating in the Hong Kong markets in 1997 but have not been detected since the chicken slaughter in 1997. The Qa/HK/G1/97-like viruses were frequently isolated from quail, while Dk/HK/Y280/97-like viruses were predominately associated with chickens. The Qa/HK/G1/97-like viruses were evolving relatively rapidly, especially in their PB2, HA, NP, and NA genes, suggesting that they are in the process of adapting to a new host. Experimental studies showed that both H9N2 lineages were primarily spread by the aerosol route and that neither quail nor chickens showed evidence of disease. The high prevalence of quail infected with Qa/HK/G1/97-like virus that contains six gene segments genetically highly related to HK/156/97 (H5N1) virus emphasizes the need for surveillance of mammals including humans.

FIG. 1

Phylogenetic trees for the H9 HA1 (A), NP (B), and PB1 (C) genes of influenza A viruses. The nucleotide sequences of the HA1, NP, and PB1 genes were analyzed with PAUP by using a maximum-parsimony algorithm. Nucleotides 55 to 1014 (960 bp) of H9 the HA1 gene, nucleotides 48 to 1398 (1,351 bp) of NP gene, and nucleotides 67 to 1428 (1,362 bp) of the PB1 gene were used for the phylogenetic analysis. The HA1 phylogenetic tree is rooted to A/Dk/Alberta/60/76 (H12N5). The NP phylogenetic tree is rooted to A/Equine/Prague/1/56 (H7N7), and the PB1 tree is rooted to B/Lee/40. Lengths of the horizontal lines are proportional to the minimum number of nucleotide differences required to join nodes. Vertical lines are for spacing branches and labels. Viruses are characterized in Tables 3 and 4; information can also be found in reference or GenBank (accession numbers D00050, M63775, M63776, M63782, M36812, M63786, M30764, M63783, M22573, and M30749). All viruses underlined in the NP and PB1 gene trees are H9N2 influenza viruses. Group I, II, and III designations are based on phylogenetic relationships of the HA1 gene.