Molecular, Pathogenesis and Immunological Studies of the Canadian Delmarva (DMV/1639) Infectious Bronchitis Virus (IBV) Variant
Date
2022-09-16
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Abstract
Infectious bronchitis virus (IBV) is a gammacoronavirus that infects chickens leading to economic losses globally. Although the disease caused by IBV is known as infectious bronchitis (IB), the virus also replicates and induces lesions in the renal, reproductive, and gastrointestinal systems of chickens. The control of IB relies mainly on using live attenuated and inactivated vaccines. The IBV Delmarva (DMV)/1639 variant has impacted the layer flocks in Eastern Canada over the past few years. The affected flocks showed a high incidence of false layer syndrome (FLS). The studies conducted in this thesis focused on three major areas: 1) molecular characterization of IBV DMV/1639 isolates obtained from clinical cases in Eastern Canada, 2) investigating the pathogenesis of the Canadian IBV DMV/1639 variant and the host responses to this virus in chickens, and 3) evaluating the protective efficacy of the existing IB vaccines against the infection with this virus in chickens. Following whole genome sequencing (WGS), phylogenetic and recombination analyses showed that the Canadian IBV DMV/1639 strain is a chimeric virus derived from a Connecticut (Conn) vaccine-like strain, a 4/91 vaccine-like strain, and one strain that is yet-unidentified. An experimental challenge of 1-day-old specific-pathogen-free (SPF) chicks showed that this virus has a wide tissue tropism and induces marked cystic lesions in the oviduct of growing pullets. A significant drop in egg production, accompanied by characteristic gross and microscopic lesions in the reproductive organs, followed the experimental challenge of SPF chickens at peak of egg production. Infected chickens showed significant recruitments of KUL01+ macrophages and CD4+ and CD8+ T cell subsets in the oviduct tissues. In addition, anti-IBV antibodies were detected systemically and locally in the oviduct washes. Heterologous IB vaccines that are commercially available in Canada protected laying SPF chickens against a drop in egg production induced by the Canadian IBV DMV/1639 strain. Vaccinated chickens had lower viral replication and mild reproductive tract lesions. Overall, the knowledge generated in this thesis contributed to the understanding of IBV-host interactions including virus evolution, pathogenesis, host responses, and vaccination-based control.
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Keywords
Delmarva 1639 infectious bronchitis virus, recombination, pathogenesis, false layer syndrome, infectious bronchitis vaccine, chicken
Citation
Hassan, M. S. H. (2022). Molecular, pathogenesis and immunological studies of the Canadian Delmarva (DMV/1639) infectious bronchitis virus (IBV) variant (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.