[Study on evolutionary origin of influenza A virus (H1N1) based on HA gene].
OBJECTIVE
To determine the evolutionary rate and divergence time of influenza A virus HA gene isolated recently worldwide pandemic and explore the origin and its transmission.


METHODS
A total of 344 H1 sequences available in the GenBank (including 248 isolated from human, 84 from swine, 11 from avian, and 1 from ferret) and 7 isolated in Shanghai were collected. The nucleotide substitution rate and time to most recent common ancestor (tMRCA) was calculated using molecular clock theory and Bayesian Skyline Plot (BSP) based on Markov chain Monte Carlo. Then genetic phylogeny was constructed referring to posterior distribution.


RESULTS
It was found that H1 sequences in the US from human, swine and avian were clustered significantly with swine H1 ones from Asia phylogenetically (Cluster US). The second cluster (Cluster Eurasian Human) nearly consisted of human H1 sequences isolated in other regions. The third cluster (Cluster Eurasian Animal) consisted of swine and avian H1 sequences from China and Italy respectively. As for all the H1 sequences, the evolutionary rate was of 2.57 x 10(-3) substitutions/site per year averagely (95% Highest Posterior Density: 1.96 x 10(-3) - 3.03 x 10(-3)/site per year). The estimated dates for tMRCA of human H1 in Europe and swine H1 in the mainland of China were the earliest, with the corresponding rates of 6.46 x 10(-3)/site per year and 0.97 x 10(-3)/site per year respectively. The tMRCAs of human and swine H1 sequences from the US were similar, with the rates of 5.86 x 10(-3)/site per year and 5.02 x 10(-3)/site per year.


CONCLUSIONS
The present flu outbreak was possibly induced by long-term circulation of influenza A virus (H1N1) in human population and swine herds in America. There was no evidence proving that influenza virus in China involved in the present outbreak.
Lu
Yi-Han
YH
Key Laboratory of Public Health Safety, Ministry of Education, Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China.
Ju
Li-Wen
LW
Jiang
Lu-Fang
LF
Yang
Ji-Xing
JX
Shi
Qiang
Q
Jiang
Qing-Wu
QW
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D019143:Evolution, Molecular; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics*; D007251:Influenza, Human / Q000821:virology*; D010802:Phylogeny; D013552:Swine
D019267:Hemagglutinin Glycoproteins, Influenza Virus