Abstract
Infectious bronchitis virus (IBV) initially establishes the infection in the respiratory tract and then spreads to other tissues depending on its virulence. During 2011–2018, the 4/91 IBV strain was isolated from poultry flocks affected by decreased egg production and quality in Eastern Canada. One of the Canadian 4/91 IBV isolates, IBV/Ck/Can/17-038913, was propagated in embryonated chicken eggs and molecularly characterized using whole genome sequencing. An in vivo study in laying hens was conducted to observe if IBV/Ck/Can/17-038913 isolate affects the egg production and quality. Hens were infected with IBV/Ck/Can/17-038913 isolate during the peak of egg lay, using a standard dose and routes maintaining uninfected controls. Oropharyngeal and cloacal swabs were collected at predetermined time points for the quantification of IBV genome loads. At 6 and 10 days post-infection, hens were euthanized to observe the lesions in various organs and collect blood and tissue samples for the quantification of antibody response and IBV genome loads, respectively. Egg production was not impacted during the first 10 days following infection. No gross lesions were observed in the tissues of the infected birds. The IBV genome was quantified in swabs, trachea, lung, proventriculus, cecal tonsils, kidney, and reproductive tissues. The serum antibody response against IBV was quantified in infected hens. In addition, histological changes, and recruitment of immune cells, such as macrophages and T cell subsets in kidney tissues, were measured. Overall, data show that IBV/Ck/Can/17-038913 isolate is not associated with egg production issues in laying hens infected at the peak of lay, while it demonstrates various tissue tropism, including kidney, where histopathological lesions and immune cell recruitments were evident.
Highlights
Infectious bronchitis (IB) is a multi-system disease in chickens caused by infectious bronchitis virus (IBV), which is a Gammacoronavirus that belongs to the family Coronaviridae and order Nidovirales [1]
IBV/Ck/Can/17-038913 isolate clustered within the GI-13 lineage along with IBVs isolated from different parts around the world that are known as 793B type
The recovery of a significant percentage of 4/91 IBV isolates from Eastern Canadian poultry flocks, which had problems with egg production in the recent past [4], led us to investigate the impact of Canadian 4/91 IBV infection in laying hens
Summary
Infectious bronchitis (IB) is a multi-system disease in chickens caused by infectious bronchitis virus (IBV), which is a Gammacoronavirus that belongs to the family Coronaviridae and order Nidovirales [1]. Outbreaks of IB in layer and broiler flocks have been reported globally with considerable economic losses due to poor growth performances in broilers, and egg production and quality defects in layers [3]. IBV is a positive-sense RNA virus with a genome of around 27.6 kilobase pairs (kb) length [9]. With the help of two virus-encoded proteases, the two polyproteins are post-translationally divided into nonstructural proteins (nsps, n = 15) that function in the replication and pathogenicity of the virus [10]. Some accessory proteins that vary in number and position among different IBV strains are encoded by the IBV genome [11]. According to the previous description, the genome of IBV is arranged in the order, 5 -1a-1ab-S-3a3b-E-M-5a-5b-N-3 with 5 and 3 genes encoding for accessory proteins that have unclear functions [12]. The 5’ and 3’ ends of the genome are flanked by short sequences (~0.5 kb) of untranslated regions (UTR) that have regulatory elements required for RNA replication and transcription [13]
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