Pathogenic characteristics of a QX-like infectious bronchitis virus strain SD in chickens exposed at different ages and protective efficacy of combining live homologous and heterologous vaccination

Lei Shao,Changqing Liu,Huiming Yang,Jinlong Cheng,Jing Zhao,Guozhong Zhang,Lihua Li,Xiuying Huang

doi:10.1186/s13567-020-00811-y

Lei Shao, Changqing Liu + Show 6 more

Open Access

https://doi.org/10.1186/s13567-020-00811-y

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Abstract

Continued reports of infections with infectious bronchitis virus (IBV) variants have occurred since its first isolation in the 1930s. Currently, QX-like IBVs are the predominant circulating genotype around the world. Here, the pathogenicity of QX-like IBV strain SD was characterized in chickens at different ages of exposure to the virus, and the protection efficacy of available vaccine combinations against IBV was evaluated. The results revealed that QX-like IBV strain SD was severely pathogenic in chickens, causing respiratory, urinary and reproductive infections, irrespective of age, based on clinical observations, viral distribution in tissues and a ciliostasis study. Severe respiratory signs, tracheal cilia injury, nephritis and abnormal development of the oviduct and ovarian follicles were evident throughout the experiment. A challenge experiment demonstrated that the homologous QX vaccine showed superior protection efficacy compared with other available vaccines, confirming the importance of IBV vaccine seed homology against the circulating IBV strains. Our findings aid an understanding of the pathogenicity of QX-like IBVs that may help to further control the infection.

Highlights

Coronaviruses (CoVs) are enveloped viruses with a positive sense, single-stranded RNA genome that can be divided into four groups: α-CoVs, β-CoVs, γ-CoVs and δ-CoVs based on genetic and antigenic criteria [1]
Our findings offer new insight into the pathogenicity of QX-like infectious bronchitis virus (IBV) in chickens exposed at different ages, and may aid the development of novel infection control strategies
Clinical signs in chickens at different ages of exposure to the virus Chickens infected at different ages with QX-like IBV strain SD showed obvious clinical signs, whereas the chickens in the control group remained healthy throughout the study

Summary

Introduction

Coronaviruses (CoVs) are enveloped viruses with a positive sense, single-stranded RNA genome that can be divided into four groups: α-CoVs, β-CoVs, γ-CoVs and δ-CoVs based on genetic and antigenic criteria [1]. CoVs primarily cause enzootic infections in birds, animals and humans [2,3,4]. Infectious bronchitis virus (IBV) belongs to the γ-CoVs that cause avian infectious bronchitis (IB), a highly contagious disease of chickens [8]. Like other positive-sense single-stranded RNA viruses, IBV has a high mutation rate that results in the continuous emergence of new serotypes and variants. IBV exists as numerous serotypes, which causes difficulties with regard to the prevention and control of the disease [15,16,17]. IB remains a serious threat to chicken production in many countries around the world [18,19,20,21,22]

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