title: [Phylogenetic analysis for H3A1 strain of all human influenza A virus].
abstract: OBJECTIVE
  Influenza A virus remains an important pathogen which threatens humans. With the help of latest developed bioinformatics tools, all available human Influenza A virus H3A1 strains were explored to deeply understanding its evolution and variation rules.
  
  
  METHODS
  All data of H3A1 sequence in NCBI Genbank and Influenza sequence database were downloaded and aligned in ClustalX with two step cluster method used to split the data and Bayesian phylogenetic tree analysis method applied to precisely construct phylogenetic tree for each clusters.
  
  
  RESULTS
  Tree topology indicated that H3 strains evolved along a single evolution trunk and tree pattern and model parameter showed obvious variety tendency with time period. However, no geographic distribution features were found for key variation strains and big branch in trees.
  
  
  CONCLUSIONS
  The evolution of human H3 strains were mainly driven by the interaction of human immune barriers and antigenic drift of virus. Since the influenza subtype had already been spread in human population, south China should not be considered as the originated areas of new strains, hence it should be treated as equally as other places in the world.
authors: Department of Health Statistic, School of Public Health, Fudan University, Shanghai 200032, China.
authors: Wen-tong
authors: WT
authors: Zhang
authors: Qing-wu
authors: QW
authors: Jiang