Abstract
The QX-type avian infectious bronchitis virus (IBV) is still a prevalent genotype in Southwestern China. To analyze the antigenicity and pathogenicity characteristics of the dominant genotype strains (QX-type), S1 gene sequence analysis, virus cross-neutralization tests, and pathogenicity test of eight QX-type IBV isolates were conducted. Sequence analysis showed that the nucleotide homology between the eight strains was high, but distantly related to H120 and 4/91 vaccine strains. Cross-neutralization tests showed that all eight strains isolated from 2015 and 2017 belonged to the same serotype, but exhibited antigenic variations over time. The pathogenicity test of the five QX-type IBV isolates showed that only three strains, CK/CH/SC/DYW/16, CK/CH/SC/MS/17, and CK/CH/SC/GH/15, had a high mortality rate with strong respiratory and renal pathogenicity, whereas CK/CH/SC/PZ/17 and CK/CH/SC/DYYJ/17 caused only mild clinical symptoms and tissue lesions. Our results indicate that the prevalent QX-type IBVs displayed antigenic variations and pathogenicity difference. These findings may provide reference for research on the evolution of IBV and vaccine preparation of infectious bronchitis (IB).
Highlights
Infectious bronchitis (IB) is a highly contagious disease that causes significant economic losses to the poultry industry worldwide [1,2]
Eight QX-type infectious bronchitis virus (IBV) were isolated from H120 and 4/91 vaccinated chickens in China, and their antigenicity and pathogenicity were analyzed for understanding the epidemiology and evolution of IBVs
Subgroup 1 (MS/15 isolate) and 3 (DYW/16 isolate) were separated in 2015 and 2016. These results indicated that there areantigenic variations in different IBV strains over time, andminor changes in the spike 1 (S1) gene maycause antigenic variation
Summary
Infectious bronchitis (IB) is a highly contagious disease that causes significant economic losses to the poultry industry worldwide [1,2]. Chickens infected with infectious bronchitis virus (IBV) become susceptible to secondary infections with bacteria, or other pathogens, because of the tracheal cilia damage, and display a higher mortality rate [3]. IBV, an etiological agent of IB, is an enveloped virus with a single-stranded positive-sense non-segmented RNA genome of approximately 27.6 kb in length and belongs to the Gammacoronavirus genus [4]. Due to the incomplete proofreading mechanism of coronavirus RNA polymerase and gene recombination during viral replication, new genotypes and serotypes of IBV variant strains appear continuously [5,6]. An array of serotypes and strains of IBV infect chickens exist throughout the world. Continuous testing of pathogenicity and serotype determination of new isolates in regions and/or countries remains crucial for better epidemiological understanding and control of IB
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