Browsing by Author "Amarasinghe, Aruna"

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    Comparative features of infections of two Massachusetts (Mass) infectious bronchitis virus (IBV) variants isolated from Western Canadian layer flocks
    (2018-12-10) Amarasinghe, Aruna; De Silva Senapathi, Upasama; Abdul-Cader, Mohamed S; Popowich, Shelly; Marshall, Frank; Cork, Susan C; van der Meer, Frank; Gomis, Susantha; Abdul-Careem, Mohamed F
    Abstract Background Infectious bronchitis virus (IBV) is one of the leading causes of mortality and morbidity in chickens. There are numerous serotypes and variants, which do not confer cross protection resulting in failure of currently used IBV vaccines. Although variant IBV isolates with major genetic differences have been subjected to comparative studies, it is unknown whether minor genetic differences in IBV variants within a serotype are different in terms of pathogenesis and eliciting host responses. Two Massachusetts (Mass) variant IBV isolates recovered from commercial layer flocks in the Western Canadian provinces of Alberta (AB) and Saskatchewan (SK) were compared genetically and evaluated for their pathogenicity, tissue distribution and ability to recruit and replicate in macrophages. Results Although whole genome sequencing of these two Mass IBV isolates showed low similarity with the M41 vaccinal strain, they had an identical nucleotide sequence at open reading frames (ORFs) 3a, 3b, envelop (E), matrix (M), 5a and 5b. The rest of the ORFs of these 2 IBV isolates showed 99.9% nucleotide similarity. However, upon experimental infection, we found that the IBV isolate originating from AB was different to the one that originated in SK due to higher tracheal lesion scores and lower lung viral replication and lower genome loads in cecal tonsils. Nevertheless, both IBV isolates elicited host responses characterized by significant macrophage recruitment to the respiratory tract and there was evidence that both IBV isolates replicated within tracheal and lung macrophages. Conclusions Overall, this study shows that Mass variant IBV isolates, although possessing minor genetic variations, can lead to significant differences in pathogenicity in young chickens. Further studies are required to investigate the pathogenicity of these two Mass variant IBV isolates in laying hens.
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    Investigations into Macrophage-Infectious Bronchitis Virus (IBV) Interaction and Shell-less Egg Syndrome
    (2018-08-29) Amarasinghe, Aruna; Abdul-Careem, Mohamed Faizal; van der Meer, Frank; Cork, S. C.; Gilch, Sabine; Gomis, Susantha Muhandiramge
    Infectious bronchitis virus (IBV) is a coronavirus and infects chickens globally causing economic losses. The disease caused by IBV is known as infectious bronchitis (IB) and is prevalent in commercial broiler and layer chickens and breeder flocks in Canada. The control of IB relies on vaccination done on the day of hatch and then several times during the grower period depending on the purpose of rearing the chickens. Although the vaccine-induced immunity protects chickens from production losses induced by IBV infection, vaccine failures are frequent. Given the issues in current IB control measures, sustainable control measures developed understanding the host-IBV interaction is required. The studies conducted in the thesis focused in two major areas; 1) understanding the interaction between IBV and host immune system mainly macrophages and 2) investigating the role of IBV in a recently emerged concern of Western Canadian table-egg layer industry, shell-less egg syndrome (SES). The work described in chapter 2 of the thesis led to the finding that IBV replicates in avian macrophages in vivo and in vitro. In vitro, we showed that IBV not only targets macrophages leading to productive infection but also affects selected functions of macrophages, particularly the production of nitric oxide (NO). As shown in chapter 3, IBV infection upregulates the expression of interleukin (IL)-1β in both tracheal and lung tissues. An additional observation made was that there was a significant association between the IBV genome load and macrophage recruitment in lungs. Overall, we found that macrophages can act as a source of cytokines, which is beneficial against IBV infection. However, the ability of IBV to replicate within macrophage by decreasing selected immune functions can be detrimental to the host. Chapter 4 provides details of our work leading to the elucidation of the etiology of SES. First, molecular characterization showed that about 70% of the IBV strains isolated from layer flocks affected with SES in Western Canada were Massachusetts (Mass) genotype. Infection of layer chickens with one of the Mass IBV isolate induced shell-less eggs. The work of chapter 5 compared two Mass IBV isolates recovered from Western Canadian layer flocks for whole genome variations and documented the differences in pathogenicity, tissue distribution, and macrophage response. The knowledge generated in the thesis increased the understanding of IBV-macrophage interaction, documented the IBV genotypes observable in Western Canada layer flocks and elucidated the etiology of SES observed in layer operations in Canada.