Characterization of highly pathogenic H5N1 avian influenza viruses isolated from poultry markets in central China.

H5N1 highly pathogenic avian influenza (HPAI) viruses have seriously affected the Asian poultry industry since their recurrence in 2003. While surveillance in southern China has revealed that H5N1 viruses underwent extensive genetic reassortment to generate many different viral genotype viruses, little is known concerning the genotypes of H5N1 virus that circulated in central China in recent years. In this study, 16 H5N1 influenza viruses were isolated from the poultry market in central China during late 2006 and early 2007, and the genotypes and pathogenicity of the viruses were identified and characterized. All eight segments of each virus were sequenced, and phylogenetic analysis showed that the two surface glycoprotein genes, hemagglutinin (HA) and neuraminidase (NA), of all the viruses were closely related to the H5N1 viruses isolated in poultry in southern China since 2006. Phylogenetic analysis of the internal protein genes indicated that four viral genotypes circulated in poultry markets in central China. The virulence of 7 of the 16 isolates was tested in chickens and mice. The results showed that the 7 isolates were highly pathogenic for SPF chickens, and had a varied virulence in mice. Our results indicate that the H5N1 viruses circulated in central China have diversified characteristics of genotype and virulence.