Immunopathogenesis of the Canadian Delmarva (DMV/1639) infectious bronchitis virus (IBV): Impact on the reproductive tract in layers.

IBV infection may lead to reduced egg production and poor egg quality in layer flocks. The DMV/1639 strain was recently identified as one of the most dominant IBV variants isolated from Canadian layer flocks with egg production problems. The current study aimed to investigate the immunopathogenesis of the Canadian DMV/1639 strain in laying chickens. Specific-pathogen-free (SPF) layers were infected at the peak of lay (29 weeks; n = 10) with an uninfected control group (n = 10). Egg production in the infected group dropped to 40% by the fifth day post-infection (dpi). Five birds from the infected and the control groups were euthanized at 5 and 10 dpi. Ovarian regression and shortened oviduct with marked histopathological changes were observed in the infected group at 10 dpi. An increase in the IBV viral load in reproductive tissues was accompanied by a significant recruitment (p < 0.05) of KUL01+ macrophages and CD4 and CD8 T cell subsets at 10 dpi. Additionally, anti-IBV antibody response was detected in serum and locally in the reproductive tract washes of the infected group. Overall, our findings contribute to the understanding of the pathogenicity of the Canadian DMV/1639 strain and the subsequent host responses in the reproductive tract of chickens.