Characterization of the hemagglutinin gene of subtype H9 avian influenza viruses isolated in 2007–2009 in China

Subtype H9 avian influenza viruses (AIVs) circulating in China have aroused concerns for their impact on poultry and risk to public health. In this report, three surveys of the viruses were reported, and the hemagglutinin gene of 55 strains of the viruses isolated in China in 2007–2009 was sequenced and analyzed. The results indicated that the prevalence of the viruses was rising in China, and most of the H9 AIVs circulating in the past decade in China belonged to sublineage h9.4.2. The viruses isolated in China in 2007–2009 were a little different from previous strains (genetic distances >7.1%). Meanwhile, a presumably predominant clade of the viruses circulating in China in 2007–2009 was identified. Mutation analysis suggested that the viruses have become of greater risk to public health in recent years.