Molecular Evolution Of H1N1 Subtype Swine Influenza Viruses Isolated From The Mainland Of China

Fifteen H1N1 subtype Swine Influenza viruses (SIVs) isolated from the mainland of China were sequenced and molecular evolutionarily analyzed in this study. These viruses in 2001 were isolated from swine in south and northeast of China.The nucleic acids of the all swine influenza viruses conducted in the research were extracted from the viruses propagated in specific-pathogen-free chicken embryos. All of the eight segments were amplified by RT-PCR (Reverse transcription-polymerase chain reaction). The cDNAs were cloned into pMD18-T vector and identified. The sequencing products were purified and run gel on CEQTM 8000 Genetic Analysis system DNA sequencing machine. Finally, using DNAStar software was used for data analysis, sequence translation, phylogenetic tree drawing and molecular evolution analysis.The phylogenetic trees revealed that all of the genes of eleven of the 15 H1N1 SIV isolates conducted in this study belonged to classical swine lineage. Furthermore, they were closely related to human strains. The result of this investigation displayed that two H1N1 SIV isolates SW/GD/714/01 and SW/GD/711/01 were possibly reassortants of classical swine H1N1 subtype and avian virus. The neuraminidase (NA) genes of two isolates were of avian origin, while the hemagglutinin (HA) and internal genes of them were of swine origin. However, PB1 genes of one isolate (SW/GD/718/01) were originated from avian influenza A virus lineage.The research showed that SW/HLJ/395/01 isolated from HeiLongjiang was reassortant of classical swine H1N1 and avianlike H1N1 viruses. The hemagglutinin (HA) and neuraminidase (NA) genes belonged to classical H1N1 subtype swine lineage, while the internal genes were located in avianlike swine lineage. In conclusion, this study elucidated the molecular evolution of H1N1 SIVs isolated from the mainland of China, clarified the category of the recent epidemical strains of H1N1 SIVs circulating in the mainland of China, and made a foundation for the further investigation. Of particular significance, these would provide the theory support for the possibility and development trend of influenza occurring in China even the whole globe.