Responses to Avian Reovirus Infection in Vivo, in Ovo, and In Vitro

Abstract

Avian reovirus (ARV) is a significant pathogen in the poultry industry, associated with economic losses due to its clinical manifestations, including tenosynovitis, immunosuppression, and enteric diseases. This dissertation investigates the pathogenic mechanisms of ARV in various avian models, including specific-pathogen-free (SPF) chickens, chicken embryos, and primary cell cultures, to advance understanding of ARV’s molecular pathogenesis. Using SPF chickens, the in vivo pathogenicity of two ARV strains (S1133 and a myocarditis-associated Alabama isolate) was assessed through oral inoculation. Viral replication, histopathology, and microbiome diversity analyses demonstrated a dose- and strain-dependent impact, with S1133 exhibiting higher replication levels in the jejunum and cardiac tissue, while associated microbial diversity was reduced. However, systemic lesions were minimal despite detectable viral presence in multiple organs. These findings underscore strain-specific ARV pathogenesis with limited systemic progression following oral inoculation. Following in ovo ARV S1133 inoculation at 18 days of embryonation, transcriptomic profiling revealed distinct tissue-specific responses. High viral replication in liver at 24 and 48 hours post-inoculation (hpi) was accompanied by activation of immune pathways related to viral replication inhibition in the liver and wound healing or blood-related pathways in the kidney and intestine. The bursa, in contrast, showed minimal differential regulation of immune pathway activation, likely due to insufficient maturation at this stage. This model elucidates ARV’s tissue-dependent replication and immune system engagement during late embryonic development. In vitro inoculation of primary chicken embryo liver (CELi), kidney (CEK), or macrophage-derived (HD11) cell cultures with ARV S1133 identified cell-type-specific viral replication and transcriptomic responses. CELi cells showed the highest viral replication, with transcriptional changes linked to antiviral responses, while HD11 cells, despite low viral load, exhibited considerable transcriptional changes related to coagulation, inflammation and growth-related pathways. Protein-protein interaction analyses identified central antiviral nodes, including IFI6, RSAD2, and MX1, which highlight key molecular targets in ARV response pathways across cell types. Collectively, these findings provide a comprehensive view of ARV pathogenicity across different models, revealing dose- and tissue-specific viral replication dynamics and immune responses. The work advances our understanding of ARV pathogenesis and the host molecular responses.