The impact of the experimental route of challenge on the host responses and pathogenesis of the Canadian Delmarva (DMV/1639) infectious bronchitis virus infection in laying chickens.

Infectious bronchitis virus (IBV) infection can be associated with respiratory, renal, and/or reproductive diseases in chickens. Under natural conditions, conjunctiva, mucosa of upper respiratory tract, and cloaca are the main routes of IBV entry. Experimentally, the study of IBV infection involved various routes of inoculation. This study investigated the impact of adding the trachea as a potential route of viral entry to the oculo-nasal infection on the host responses, pathogenicity, and tissue tropism of the Canadian IBV Delmarva (DMV/1639) strain in laying chickens. Specific-pathogen-free laying chickens were divided into three experimental groups: control group (Con group), oculo-nasal challenged group (ON group), and oculo-nasal/intratracheal challenged group (ON/IT group); all groups were observed for 12 days post-infection (dpi). The clinical signs and reduction in egg production in the ON/IT group started slightly earlier compared to the ON group. At 12 dpi, the gross lesions in the ON/IT group were confined to the ovary, while the ON group showed regressed ovary and atrophied oviduct. Only the ON group showed significantly higher microscopic lesion scores in the lung, kidney, magnum, and uterus compared to the control group at 12 dpi. The oviduct tissues of the ON group showed a significant increase in B cells infiltration compared to ON/IT and control groups. The viral shedding (detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR)), tissue tropism (detected either by qRT-PCR or immunohistochemistry (IHC)), T/natural killer cells infiltration in reproductive tract (detected by IHC), and antibody-mediated immune responses (measured by enzyme-linked immunosorbent assay) showed similar patterns in the ON and ON/IT groups.

Comparative pathogenicity of infectious bronchitis virus Massachusetts and Delmarva (DMV/1639) genotypes in laying hens.

Infectious bronchitis (IB) is a highly contagious and acute viral disease of chicken caused by the infectious bronchitis virus (IBV) of the family Coronaviridae. Even with extensive vaccination against IB by the poultry industry, the occurrence of new IBV genotypes is a continuous challenge encountered by the global poultry industry. This experiment was designed to compare the pathogenicity of two IBV strains belonging to Massachusetts (Mass) and Delmarva DMV/1639 genotypes. Specific pathogen-free laying hens were challenged during the peak of production (30 weeks), keeping a mock-infected control group. During 21 days of observation following infection, a significant drop in egg production with miss-shaped and soft shells was observed in the DMV/1639 IBV-infected hens only. The DMV/1639 IBV infected group showed prolonged and higher cloacal viral shedding compared with the Mass IBV-infected group. At the end of the study (21 days post-infection), the viral genome loads in the respiratory, urogenital, and immune tissues were significantly higher in the DMV/1639 IBV-infected group compared with the Mass IBV-infected group. Macroscopic lesions such as distorted ova leading to egg peritonitis were observed only in the DMV/1639 IBV-infected group. Moreover, microscopic lesion scores were significantly higher in the lung, kidney, cecal tonsils, and oviduct of the DMV/1639 IBV-infected group compared with the Mass IBV-infected group. Finally, the apoptosis index in the kidney, ovary, magnum, isthmus, and shell gland was significantly higher in the DMV/1639 IBV-infected group compared with the control and Mass-infected groups. This study examined the pathogenicity of two IBV genotypes that are impacting the layer industry in North America.