Comparative features of infections of two Massachusetts (Mass) infectious bronchitis virus (IBV) variants isolated from Western Canadian layer flocks

Abstract

BackgroundInfectious 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.ResultsAlthough 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.ConclusionsOverall, 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.Electronic supplementary materialThe online version of this article (10.1186/s12917-018-1720-9) contains supplementary material, which is available to authorized users.

Genetic and antigenic heterogeneity of GI-1/Massachusetts lineage infectious bronchitis virus variants recently isolated in China

“…The S1 sequences of the isolates LJL/130906 and I1124/16 showed obvious point mutations when compared with those of the M41 and H120 strains ( Xu et al, 2018 ), however, other genes and regions were found to be affected by mutations in the genomes of Mass-type strains which was consistent with previous observations ( Amarasinghe et al, 2018 ). It is important to note that the sequence of the S1 subunit in the isolate I1124/16 was identical to that of the 14 Mass-type IBV strains in America and a Thailand strain.…”

Delmarva (DMV/1639) Infectious Bronchitis Virus (IBV) Variants Isolated in Eastern Canada Show Evidence of Recombination

“…Although the classification of IBV variants based on partial or full S1 gene sequences is feasible, in depth molecular analysis of IBV variants requires the examination of the complete genome of the IBV. Previously, two Mass IBV variants isolated from western Canada were characterized using whole genome sequencing [20]. In the current study, the genomic makeup of DMV/1639-like isolates from diagnostic samples are characterized in detail, and several potential recombination sites are identified.…”

A Recombinant La Sota Vaccine Strain Expressing Multiple Epitopes of Infectious Bronchitis Virus (IBV) Protects Specific Pathogen-Free (SPF) Chickens against IBV and NDV Challenges

“…IBV causes upper respiratory illness, nephritic syndrome, and a drop in egg production in layer chickens [1]. The mortality rate can be high in young chickens, especially with other secondary complications such as viral and bacterial infections [6][7][8][9][10].…”