Epidemic Trend of the Infectious Bronchitis Virus in Chickens in China from 2021 to 2023
The infectious bronchitis virus(IBV)is an important pathogen causing respiratory and genitourinary diseases in chickens.The virus is prone to mutation and recombination,which results in the continuous emergence of new mutants.These strains show significant antigenic differences from conventional vaccine strains,thereby posing substantial challenges to prevention and control.Therefore,continuous molecular epidemiological surveillance of IBV strains prevalent in China has important guidance and reference values for the targeted development of new IBV vaccines.The S1 protein-coding genes of 32 IBV strains isolated in China from 2021 to 2023 were sequenced and analyzed.Their common variation sites were predicted for protein function.Twenty-two of the 32 IBV strains were located in the GI-19 cluster and were divided into two small subclusters independently.The homology of the strains within the subcluster was＞98.08％.The homology between subclusters was between 96.35％and 98.02％.However,the homology with the early classical GI-19 virulent strain isolated by our research team(SD strain)was＜95.33％.The homology with the naturally attenuated vaccine strain SZ was between 95.99％and 98.04％.Two strains were clustered with the GI-22 genotype strain LDT3.The other three isolates were GI-1 and GI-13 vaccine-like strains.The isolation rate of the GVI-1 genotype increased(4/32),of which the homology with conventional vaccine strains was about 68％.Another isolated strain shared＜78％homology with other genotype strains,and further analysis of their pathogenicity and immunogenicity was needed.In summary,the epidemic strains of IBV in China are dominated by GI-19 genotype strains but.simultaneously,great changes have taken place between new isolates and classical strains,showing an evolution trend of independent small branches,which merits attention.
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