Evolution of the hemagglutinin gene of influenza A( H7N9) virus in China between 2013 and 2017 / 医学研究生学报

ABSTRACT

Objective Influenza A(H7N9) virus causes a relatively high mortality in humans and therefore it is of great sig-nificance to know its prevalence in China .This article aimed to study the genetic characteristics and evolution of the hemagglutinin (HA) gene of the influenza A(H7N9) virus prevailing in China between 2013 and 2017. Methods We downloaded the HA se-quences of the influenza A ( H7N9) virus prevailing in China between 2013 and 2017 from The Global Initiative on Sharing All Influen-za Data and National Center for Biotechnology Information .Using the bioinformatics software , we analyzed the homology , molecular characteristics , phyletic evolution , and selective pressure of the HA gene. Results The homology of the HA gene of the influenza A ( H7N9) virus and the reference strain was decreasing each year from 2013 to 2017, 99.0%-99.9%in 2013, 98.7%-99.5%in 2014, 98.4%-99.6%in 2015, 76.8%-99.4%in 2016, and 69.9%-98.2%in 2017.Compared with the reference strain , the HA gene of the influ-enza A(H7N9) virus underwent variations in 21 antigenic sites.The variation of N285D was the highest (23%) in 2015 and that of R148K increased yearly,reaching 65%in 2016 and 78.5% in 2017. Phylogenetic analysis showed a concentrative distribution of the influenza A ( H7N9) virus strains on the phylogenetic tree in the same year from 2013 to 2017.Amino acid substitution of T 140A was observed in most of the influenza A ( H7N9) virus strains from Guang-dong in 2013, and the widest distribution of the virus strains was found in 2014.Positive selective pressure site 65 was obtained in the sequence of 2015 using the FEL and IFEL models, but not in the strains of 2016 or 2017. Conclusion Influenza A(H7N9) virus constantly undergoes variation , which has increased the difficulty in its prevention and control .More importance should be attached to observation of the virus and response to its adaptive mutations .