Nine infectious bronchitis virus (IBV) strains belonging to the GI-7 lineage were isolated between 2009 and 2017 in China. Phylogenetic analysis and comparisons of full-length sequences of the S1 gene suggested that the GI-7 lineage should be further classified as TW-I and TW-II sublineages, which correspond to the previous TW-T and TW-II genotypes. The nine IBV strains were clustered in the TW-II sublineage. Further investigation revealed that viruses in the TW-I and TW-II were not only genetically, but also antigenically different. Moreover, the TW-II sublineage contained various clades and recombinants. A recombinant was found to originate from recombination events between field strains (TW-II ck/CH/LJL/090608- and GI-19 ck/CH/LDL/091022-likes viruses) in which the recombination in the S1 subunit coding sequences had led to changes in antigenicity of the viruses. A more in-depth investigation demonstrated that TW-II viruses appear to have undergone a significant evolution following introduction in mainland China, which resulted into the viruses diverging into different clades. The viruses between the different clades in TW-II sublineage exhibited a significant change in genetic and antigenic characteristics. In addition, the five TW-II viruses selected on the basis of the results of S1 nucleotide sequence phylogenetic trees showed different pathogenicity to SPF chickens although they could induce nephritis in the infected chickens and identified as nephropathogenic strains.

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