title: Genetic analysis of influenza A/H3N2 and A/H1N1 viruses circulating in Vietnam from 2001 to 2006.
abstract: Influenza A virus has the ability to overcome immunity from previous infections through the acquisition of genetic changes. Thus, understanding the evolution of the viruses in humans is important for the surveillance and the selection of vaccine strains. A total of 30 influenza A/H3N2 viruses and 35 influenza A/H1N1 viruses that were collected in Vietnam from 2001 to 2006 were used to analyze the evolution of the hemagglutinin (HA), neuraminidase (NA), and matrix protein (M) genes. Phylogenetic analysis of individual gene segments revealed that the HA and the NA genes of the influenza A viruses evolved in a sequential way. However, the evolutionary pattern of the M gene proved to be nonlinear and was not linked with that of the HA and NA genes. Genetic drift in HA1 segments, especially in the antigenic sites of A/H3N2 viruses, occurred more frequently in A/H3N2 viruses than it did in A/H1N1 viruses. Two reassortants, one influenza A/H3N2 strain and one A/H1N1 strain, were found on the basis of the phylogenetic analysis of the three genes. While both genetic mutation and reassortment contributed to their evolution, the frequency of genetic changes and reassortment events differs between the two subtypes. As influenza viruses circulate throughout the year, we emphasize the importance of surveillance in tropical and subtropical zones, where the emergence of new strains may be detected earlier than it is in temperate zones.
authors.affiliation: Department of Public Health, Niigata University, Graduate School of Medical and Dental Sciences, 1-757, Asahimachi-Dori, Niigata City, Niigata Prefecture 951-8510, Japan. bbmm@med.niigata-u.ac.jp
authors.forename: Danjuan
authors.initials: D
authors.lastname: Li
authors.forename: Reiko
authors.initials: R
authors.lastname: Saito
authors.forename: Mai T Q
authors.initials: MT
authors.lastname: Le
authors.forename: Hang L K
authors.initials: HL
authors.lastname: Nguyen
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Yugo
authors.initials: Y
authors.lastname: Shobugawa
authors.forename: Duc T
authors.initials: DT
authors.lastname: Dinh
authors.forename: Phuong V M
authors.initials: PV
authors.lastname: Hoang
authors.forename: Huong T T
authors.initials: HT
authors.lastname: Tran
authors.forename: Ha K
authors.initials: HK
authors.lastname: Nghiem
authors.forename: Long T
authors.initials: LT
authors.lastname: Hoang
authors.forename: Lien P
authors.initials: LP
authors.lastname: Huynh
authors.forename: Hien T
authors.initials: HT
authors.lastname: Nguyen
authors.forename: Makoto
authors.initials: M
authors.lastname: Nishikawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000956:Antigens, Viral / Q000235:genetics; D000939:Epitopes / Q000235:genetics; D019143:Evolution, Molecular; D040961:Genetic Drift; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics* / Q000302:isolation & purification*; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics* / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D008969:Molecular Sequence Data; D009439:Neuraminidase / Q000235:genetics; D010802:Phylogeny; D016865:Reassortant Viruses / Q000235:genetics; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D014744:Vietnam / Q000453:epidemiology; D014763:Viral Matrix Proteins / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics
chemical_list: D000956:Antigens, Viral; D000939:Epitopes; D019267:Hemagglutinin Glycoproteins, Influenza Virus; C488936:M1 protein, Influenza A virus; D014763:Viral Matrix Proteins; D014764:Viral Proteins; C483468:hemagglutinin, human influenza A virus; C487630:NA protein, influenza A virus; D009439:Neuraminidase