Antigenic and Genetic Characteristics of Swine-Origin 2009 A(H1N1) Influenza Viruses Circulating in Humans

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Science  10 Jul 2009:
Vol. 325, Issue 5937, pp. 197-201
DOI: 10.1126/science.1176225
  • Fig. 1

    Host and lineage origins for the gene segments of the 2009 A(H1N1) virus: PB2, polymerase basic 2; PB1, polymerase basic 1; PA, polymerase acidic; HA, hemagglutinin; NP, nucleoprotein; NA, neuraminidase; M, matrix gene; NS, nonstructural gene. Color of gene segment in circle indicates host. Determination of lineage is explained in the main text.

  • Fig. 2

    A maximum likelihood phylogenetic tree for nucleotide sequences of the HA gene of selected influenza viruses. The selected viruses were chosen to be representative from among all available relevant sequences in GenBank: sequences that had both high and low divergence to avoid biasing the distribution of branch lengths; swine strains that had been isolated from humans and that had been isolated from swine; strains that were representative of the major gene lineages from different hosts; and the nearest BLAST relative to include the most closely related non-outbreak virus. Phylogenetic trees of a larger number of representative HA gene segments, and of all H1 HA swine gene segments, are shown in figs. S1D and S2D, respectively. Tree was inferred using PAUP* (version 4.0b10) (40), using GTR+I+Γ4 (the general time-reversible model with the proportion of invariant sites and the gamma distribution of among-site rate variation with four categories estimated from the empirical data) as determined by ModelTest (41). Global optimization of the tree topology was performed by tree bisection-reconnection branch swapping. The robustness of individual nodes of the tree was assessed using a bootstrap resampling analysis (1000 replicates, with topologies inferred using the neighbor-joining method under the GTR+I+Γ4 substitution model).

  • Fig. 3

    Antigenic map of 71 early swine-origin 2009 A(H1N1) influenza viruses and 11 antisera. An antigenic map is a geometric representation of binding assay data, in this case the HI assay data in tables S3 and S4. In such a map, the relative positions of strains (colored circles) and antisera (uncolored squares) are adjusted such that the distances between strains and antisera in the map represent the corresponding HI measurements with the least error. Distance in the map thus represents antigenic distance, and the closer antigens are to each other in the map, the more similar they are antigenically (38). The color of a circle in the map indicates whether the strain is a 2009 A(H1N1) influenza virus (blue) or an A(H1) swine influenza virus isolated between 1998 and 2007 from either a swine (purple) or a human (pink) infected with a swine influenza virus. The vertical and horizontal axes both represent antigenic distance, and because only the relative positions of antigens and antisera can be determined, the orientation of the map within these axes is free (thus an antigenic map can be rotated in the same way that a geographic map can be rotated). The spacing between grid lines is one unit of antigenic distance—corresponding to a twofold dilution of antiserum in the HI assay. Two units correspond to fourfold dilution, three units to eightfold dilution, etc. A difference higher than fourfold in HI titer is usually considered to be sufficient to necessitate an update of the human seasonal influenza virus vaccine. Antigenic clusters of human seasonal influenza viruses typically have a radius of two antigenic units (fourfold in HI) (38) (see fig. S3 for a zoomable PDF of this antigenic map that additionally includes the names of each strain and antiserum).

Additional Files

  • Antigenic and Genetic Characteristics of Swine-Origin 2009 A(H1N1) Influenza Viruses Circulating in Humans
    Rebecca J. Garten et al.

    Supporting Online Material

    This PDF file includes:
    Figs. S1 to S3
    Tables S1 to S6

    Corrected 8 July 2009:
    Phylogenetic trees in fig. S2 have been annotated with lineage names; the color scheme in fig. S3 has been changed to match that of the corresponding figure in the main text (which was changed in figure proofing for better contrast when published); line 2 of table S2 has been changed from M582L to M581L to correct error; titers of "5" in tables S3 and S4 have been changed to the more standard nomenclature of " <_10 some="some" isolation="isolation" dates="dates" have="have" been="been" corrected="corrected" in="in" tables="tables" s3="s3" and="and" s4="s4" miscellaneous="miscellaneous" minor="minor" formatting="formatting" changes="changes" made.the="made.the" original="original" version="version" can="can" be="be" found="found" a="a" href="/cgi/data/1176225/DC1/1">here

    This file is in Adobe Acrobat PDF format.

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