Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, the People's Republic of China.
Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, the People's Republic of China.
Poult Sci. 2020 Nov;99(11):5440-5451. doi: 10.1016/j.psj.2020.08.037. Epub 2020 Sep 1.
Four GI-1/Massachusetts-type (GI-1/Mass-type) infectious bronchitis virus (IBV) strains were isolated and the complete genomes of these isolates, coupled with the Mass-type live-attenuated vaccine H120 and the Mass-type pathogenic M41 strains, were sequenced in the present study. Our results show that isolates LJL/140820 and I0306/17 may be derived from the Ma5 (another Mass-type live-attenuated vaccine strain) and H120 vaccine strains, respectively. The I1124/16 strain was found to be a M41 variant that likely resulted from nucleotide accumulated mutations in the genome. Consistently, the results of the virus neutralization test showed that isolate I1124/16 was antigenically related but slight different from the M41. Our results from the protection experiments pointed out that chickens immunized with H120 failed to eliminate viral shedding after infection with the isolate I1124/16, which was different from that of M41; this result was consistent to the field observation and further implicated that the variant IBV isolate I1124/16 was antigenic different from the M41 strain. Furthermore, the I1124/16 was found to have comparable but slightly lower pathogenicity with the M41 strain. More studies based on the reverse genetic techniques are needed to elucidate the amino acids in the S1 subunit of spike protein contributing to the altered antigenicity of the isolate I1124/16. In addition, an IBV isolate, LJL/130609, was found to be originated from recombination events between the I1124/16- and Connecticut-like strains. Our results from the virus neutralization test also showed that isolates LJL/130609 and I1124/16 were antigenic closely related. Hence, there are at least 3 different genetic evolution patterns for the circulation of the GI-1/Mass-type IBV field strains in China. The differences of vaccines used, the field conditions and genetic pressures between different flocks, likely account for the emergence, evolution patterns, and characteristics of the Mass-type IBV strains.
本研究分离了 4 株 GI-1/马萨诸塞型（GI-1/Mass-type）传染性支气管炎病毒（IBV）株，并对这些分离株的完整基因组，以及 Mass 型活疫苗 H120 和 Mass 型强毒 M41 株进行了测序。我们的结果表明，分离株 LJL/140820 和 I0306/17 可能分别来源于 Ma5（另一种 Mass 型活疫苗株）和 H120 疫苗株。I1124/16 株被发现是 M41 的一个变异株，可能是由于基因组中核苷酸的积累突变而导致的。同样，病毒中和试验的结果表明，分离株 I1124/16 在抗原性上与 M41 相关，但略有不同。我们的保护实验结果表明，用 H120 免疫的鸡在感染分离株 I1124/16 后未能消除病毒脱落，这与 M41 不同；这一结果与田间观察一致，并进一步表明变异的 IBV 分离株 I1124/16 在抗原性上与 M41 株不同。此外，I1124/16 的致病性与 M41 株相当，但略低。需要更多基于反向遗传技术的研究来阐明 spike 蛋白 S1 亚单位中的氨基酸对分离株 I1124/16 抗原性改变的贡献。此外，发现 IBV 分离株 LJL/130609 是由 I1124/16-和康涅狄格样株之间的重组事件产生的。我们的病毒中和试验结果也表明，分离株 LJL/130609 和 I1124/16 在抗原性上密切相关。因此，在中国，GI-1/马萨诸塞型 IBV 田间株至少有 3 种不同的遗传进化模式。疫苗使用的差异、不同鸡群的田间条件和遗传压力可能是 Mass 型 IBV 株出现、进化模式和特征的原因。
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