Fig 1.
Phylogenetic trees of H4 (A) and N6 (B) genes of H4N6 AIVs in China. Phylogenetic trees were generated by the neighbor-joining method and bootstrapped with 1000 replicates using MEGA6. Analysis was based on nucleotides 1–1693 of the HA gene and 1–1413 of the NA gene. Virus subtypes that are not H4N6 are indicated in brackets. Virus strains isolated in this study are highlighted in red.
Fig 2.
Phylogenetic trees of PB2 (A), PB1 (B) and PA (C) genes of H4N6 AIVs in China. Phylogenetic trees were generated by the neighbor-joining method and bootstrapped with 1000 replicates using MEGA6. Analysis was based on nucleotides 1–2277 of the PB2 gene, 1–2274 of the PB1 gene, and 1–2151 of the PA gene. Virus subtypes that are not H4N6 are indicated in brackets. Virus strains isolated in this study are highlighted in red.
Fig 3.
Phylogenetic trees of NP (A), M (B), and NS (C) genes of H4N6 AIVs in China. Phylogenetic trees were generated by the neighbor-joining method and bootstrapped with 1000 replicates using MEGA6. Analysis was based on nucleotides 1–1497 of the NP gene, 1–982 of the M gene, and 1–838 of the NS gene. Virus subtypes that are not H4N6 are indicated in brackets. Virus strains isolated in this study are highlighted in red.
Fig 4.
The genotypic evolution of H4N6 AIVs in China from 2000 to 2016.
The eight gene segments listed are (top to bottom): PB2, PB1, PA, HA, NP, NA, M, and NS genes. The colors of the eight gene segments of the first isolate (A/duck/Nanchang/4-165/2000) were defined to be the same, and a new color represent a different lineage from this strain. The abbreviation of virus which possessed the corresponding genotype are listed below the genotype. The gene constellation for different genotypes, the viruses that possessed these, and the abbreviation of virus name are given in S1 Table.
Fig 5.
Schematic representation of putative genomic compositions of the four H4N6 AIVs isolated in this study and their possible parent viruses.
The eight gene segments (from top to bottom) in each virus are PB2, PB1, PA, HA, NP, M, and NS. Each color represents a separate virus background. The simplified schematic illustration is based on nucleotide-distance comparison and phylogenetic analysis.
Fig 6.
Weight loss and lung virus titration in mice inoculated with H4N6 AIVs.
Six-week-old female BALB/c mice (n = 3 mice/group) were inoculated i.n. with 106 EID50 of virus. The body weights of inoculated mice were measured daily and are represented as percentages of weight on the day of inoculation (day 0). The averages for each group are shown (A).The lungs of each mouse in each group were collected at 3 and 5 dpi, respectively, for virus titration (B).
Fig 7.
Contact transmission of H4N6 AIVs in guinea pigs.
Three guinea pigs were intranasally inoculated with 106 EID50 of A/mallard/Beijing/10/2016 (A) or A/mallard/Beijing/16/2016 (B) viruses. At 24 hpi, the inoculated guinea pigs were placed in a cage with three naive guinea pigs. Nasal wash titers are plotted as a function of time post-inoculation. Titers of intranasally inoculated animals are represented by solid lines and filled squares; titers of exposed guinea pigs are shown with dashed lines and filled triangles.