Antigenic and Pathogenic Characteristics of QX-Type Avian Infectious Bronchitis Virus Strains Isolated in Southwestern China

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).The spike 1 (S1) gene is highly variable among IBV strains and encodes epitopes, which can induce the production of specific neutralizing antibodies [7]. The partial or the full-length of the S gene has been used in the molecular characterization of IBV isolates. The antigenic relatedness and receptor binding with host cells are influenced by hypervariable regions (HVRs) in the S1 gene [8-10]; further, the S gene and 5a accessory gene are responsible for the attenuation of virulent IBV via a suitable reverse-genetic system [11]. Therefore, the differences in the genotypes, antigenicity, and pathogenicity existing among IBVs are mainly related to the S1 subunit of the IBV spike protein.Since the early 1980s, IBV has been continuously isolated in China, and QX genotype has become the prevalent genotype [12][13][14]. Our previous study showed that isolates obtained from Southwestern China between 2008 and 2016 mainly belong to the QX genotype [12,15]. Other reports have shown that QX-type IBVs epidemic is a major problem in the poultry industry in Europe, Japan, Korea, Russia, Africa, and the Middle East [16][17][18]. However, even with the wide use of IBV vaccines, such as H120 and 4/91 for QX-type IBV infection, immune failure occurred frequently [4,19]. QX-like IBV has become a challenge to the prevention and control IBV. Therefore, it is crucial to gain a better understanding of the antigenicity and pathogenesis of QX-like IBV. Previously, comparative studies have been conducted to elucidate differential pathogenicity among two QX-like IBVs with 94.1% similarities of the S1 gene [20]. Very minor changes in the IBV genome can lead to differences in pathogenicity [21]; therefore, comparative studies involving more QX-type IBVs are required. The present study was conducted with the aim to elucidate the S1 gene differences of eight Q...

A highly pathogenic GI-19 lineage infectious bronchitis virus originated from multiple recombination events with broad tissue tropism

“…Coincidently, no obvious gross lesions were observed and viral antigens were not detected by IHC in the proventriculi of chickens infected with the isolate I0305/19, although the isolate I0305/19 can replicate efficiently in the proventriculi by viral titration using 9-day-old SPF chicken eggs. In addition, only very mild respiratory signs were observed in both the commercial broilers and the SPF chickens infected with isolate I0305/19; however, other reports demonstrated that the GI-19 viruses could induce obvious respiratory signs (Liu and Kong et al, 2004;Benyeda et al, 2009;Choi et al, 2009;Zhong et al, 2016;Khanh et al, 2018;Xu et al, 2018;Li et al, 2019;Ren et al, 2019a;Yan et al, 2019). The isolate I0305/19 can replicate efficiently in both the trachea and lungs in the infected SPF chickens, which was demonstrated by viral titration in SPF chicken eggs and viral antigen detection by IHC.…”

“…GI-19 field strains showed different levels of virulence to SPF chickens in experimental infections. Some strains isolated in China were nonpathogenic to SPF chicken (Yan et al, 2017), while others showed low to high pathogenicity to SPF chickens, with morbidity ranging from 40 % to 100 % and mortality ranging between 10 % and 80 % (Table 1) (Liu and Kong, 2004;Zhong et al, 2016;Yan et al, 2017;Xu et al, 2018;Li et al, 2019;Ren et al, 2019aRen et al, ,2019b. The GI-19 virus strain isolated in Malaysia was also highly virulent to SPF chickens with 100 % morbidity and 41.3 % mortality (Khanh et al, 2018).…”

“…IBV GI-19 viruses were initially thought to be associated with proventriculitis outbreaks (Wang et al, 1998); however, with progress in time, it was demonstrated that these viruses are responsible for respiratory signs and nephritis (Liu and Kong, 2004;Benyeda et al, 2009;Khanh et al, 2018). Morbidity caused by IBV GI-19 viruses is 100 % and mortality is usually between 5% and 70 % (Liu and Kong et al, 2004;Benyeda et al, 2009;Choi et al, 2009;Zhong et al, 2016;Khanh et al, 2018;Xu et al, 2018;Li et al, 2019;Ren et al, 2019aRen et al, ,2019bYan et al, 2019). The present report describes the isolation and investigation of a highly pathogenic IBV strain (I0305/19) belonging to the GI-19 lineage.…”

Infectious Bronchitis Coronavirus Infection in Chickens: Multiple System Disease with Immune Suppression

“…The nephropathogenic IBV strains include B1648, Aus T, QX-like, 4/91, Holte and Gray [ 6 , 24 , 25 , 32 , 50 ]. The IBV B1648 strain is known to spread from the respiratory tissues via blood monocytes [ 50 ].…”

“…Therefore, knowledge of different IBV strains and their pathogenicity is important for establishing sustainable vaccination strategies. Despite several published reviews relevant to IBV pathogenesis [ 18 , 19 , 20 , 21 , 22 ], there is a need for an analysis of information due to the large influx of literature in recent years on the evolving pathogenesis of IBV infection [ 23 , 24 , 25 ].…”