Abstract：Objective To explore the origin, evolution and geographical spread of avian influenza virus subtype H9 (AIV-H9) in mainland China at the molecular level, and to provide a scientific basis for prevention and control of avian influenza viruses. Methods The HA gene sequences of AIV-H9 were collected from the global public influenza virus database. 180 sequences containing accurate sampling information from 1997 to 2018 were obtained by comparing, clustering, and screening the downloaded sequences. Bioinformatic software such as BEAST was used for virus selection stress analysis, Bayesian time evolution tree construction and time-space dynamic reconstruction of virus evolution. Results The nucleotide differences of the sequences ranged from 0.2% to 20.7%, while the amino acid differences from 0.0% to 15.8%. The nucleotide substitution rates of the coding regions were: 0.540, 0.607 and 1.853, respectively. The mean ratio of the non-synonymous mutation rate to the synonymous mutation rate was 0.1789, but the ratio was greater than 1 at 7 positions. The mean evolution substitution rate of the HA gene was2.476×10-3 subs per site per year, and the time to the most recent common ancestors appeared in 1947.457. The topology of the established phylogenetic tree was divided into multiple branches. The most likely root node was Guangdong province, with a posterior probability of 21.7%. The spatio-temporal dynamic analysis based on the current data showed that the virus firstly spread from Guangdong to Anhui, secondly to Guangxi and Jiangsu, and then to several surrounding provinces with Jiangsu as the center, and finally spread among several provinces between 1959 and 2018. Six routes from Jiangsu had statistically significant support. Conclusions The AIV-H9 originated much earlier than they were firstly reported in China. The spread of AIV-H9 among provinces in China is complicated, and Jiangsu province is an important center for transmission and spread of AIV-H9.
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2019, Vol. 26 
