1 State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071 China; 
2 Beijing Institute of Genome, Chinese Academy of Sciences, Beijing 100029.

The epidemic situation of A H1N1 flu arose in North America in April 2009, which rapidly expanded to three continents of Europe, Asia and Africa, with the risk ranking up to 5. Until May 13th, the flu virus of A H1N1 had spread into 33 countries and regions, with a laboratory confirmed case number of 5728, including 61 deaths. Based on IRV and EpiFluDB database, 425 parts of A H1N1 flu virus sequence were achieved, followed by sequenced comparison and evolution analysis. The results showed that the current predominant A H1N1 flu virus was a kind of triple reassortment A flu virus: (i) HA, NA, MP, NP and NS originated from swine influenza virus; PB2 and PA originated from bird influenza virus; PB1 originated from human influenza virus. (ii) The origin of swine influenza virus could be subdivided as follows: HA, NP and NS originated from classic swine influenza virus of H1N1 subtype; NA and MP originated from bird origin swine influenza virus of H1N1 subtype. (iii) A H1N1 flu virus experienced no significant mutation during the epidemic spread, accompanied with no reassortment of the virus ge-nome. In the paper, the region of the representative strains for sequence analysis (A/California/04/2009 (H1N1) and A/Mexico/4486/2009 (H1N1)) included USA and Mexico and was relatively wide, which sug-gested that the analysis results were convincing.

Supported by the National Key Basic Research and Development of China (Grant Nos. 2007FY210700, 2005CB523007), Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KSCX2-YW-N-065), e-Science Project of the Chinese Academy of Sciences (Grant No. IN-FO-115-D02) and Sixth Framework Program in European (Grant Nos. SP5B-CT-2006-044161, SP5B-CT-2006-044405).