Establishment of influenza A virus (H6N1) in minor poultry species in southern China.

An H6N1 virus, A/teal/Hong Kong/W312/97 (W312), was isolated during the "bird flu" incident in Hong Kong in 1997. Genetic analysis suggested that this virus might be the progenitor of the A/Hong Kong/156/97 (HK/97) H5N1 virus, as seven of eight gene segments of those viruses had a common source. Continuing surveillance in Hong Kong showed that a W312-like virus was prevalent in quail and pheasants in 1999; however, the further development of H6N1 viruses has not been investigated since 2001. Here we report influenza virus surveillance data collected in southern China from 2000 to 2005 that show that H6N1 viruses have become established and endemic in minor poultry species and replicate mainly in the respiratory tract. Phylogenetic analysis indicated that all H6N1 isolates had W312-like hemagglutinin and neuraminidase genes. However, reassortment of internal genes between different subtype virus lineages, including H5N1, H9N2, and other avian viruses, generated multiple novel H6N1 genotypes in different types of poultry. These novel H6N1/N2 viruses are double, triple, or even quadruple reassortants. Reassortment between a W312-like H6N1 virus and an A/quail/Hong Kong/G1/97 (HK/97)-like H9N2 virus simultaneously generated novel H6N2 subtype viruses that were persistent in poultry. Molecular analyses suggest that W312-like viruses may not be the precursors of HK/97 virus but reassortants from an HK/97-like virus and another unidentified H6 subtype virus. These results provide further evidence of the pivotal role of the live poultry market system of southern China in generating increased genetic diversity in influenza viruses in this region.