New molecular evolutionary characteristics of H9N2 avian influenza virus in Guangdong Province, China.

To understand the evolution of H9N2 avian influenza virus genotype and its molecular evolution rate, we systematically analyzed 72 H9N2 avian influenza virus sequences isolated from Guangdong province from 2014 to 2018. We found three genotypes (G57, G68, and G118) of the H9N2 avian influenza virus, of which G118 is a newly discovered genotype and G57 is the dominant genotype. The internal gene cassette of the G57 genotype H9N2 avian influenza virus is a stable combination that can easily transport internal genes to other novel avian influenza viruses, and the internal gene cassettes of the G68 and G118 are identical to those of G57.In addition, we estimated the nucleotide substitution rate of the HA and NA genes of the H9N2 influenza virus from 2014 to 2018.The nucleotide substitution rate of HA and NA genes showed an upward trend in 2015 and 2016. In the past two years, H9N2 avian influenza virus recombination has produced genotype G68, which disappeared in 2014 for one year. And very coincidentally, in 2015, there was a new genotype G118. We observed that the emergence of new genotypes was accompanied by a slight increase in overall nucleotide substitution rate. Therefore we hypothesize that the emergence of new genotypes could accelerate the molecular evolution rate of genes. Our research shows that the H9N2 avian influenza virus in Guangdong province has been undergoing intense evolution, demonstrating the need to strengthen influenza surveillance in the region.