Comparative analysis of viral biological characteristics and pathogenicity of representative prevalent avian reovirus strains from genotypes I to V

The variable pathogenicity of avian reovirus (ARV), driven by genotypic diversity, poses significant control challenges to the global poultry industry. However, biological and pathogenic distinctions among genotypes remain poorly characterized. We performed a comprehensive comparison of 14 ARV strains (genotypes I-V), evaluating viral biological characteristics and pathogenicity indicators. Phylogenetic analysis of these isolates and field strains in China based on the σC gene revealed co-circulation of multiple genotypes (predominantly I and II), with epidemic strains actively evolving and genetically distant from the S1133 vaccine. Structural analysis localized conformational B-cell epitopes of σC protein primarily to the C-terminal globular head and neck, with a highly conserved core antigenic scaffold formed by key residues, while peripheral residues showed genotype-specific variation. Recombination analysis suggests that genotype V (SDAU-G5-DG) likely emerged through recombination with genotype VI. Genotypes I (SDAU-G1-AN4) and IV (SDAU-G4-m4) exhibited enhanced replication and lethality in cell culture and chicken embryos. In vivo, all strains caused growth retardation, lameness, tenosynovitis, and immune organ atrophy, but the tested genotypes I and IV were most virulent. Distinct tissue tropisms were observed: genotypes I and V induced cardiac and hepatic lesions, whereas genotypes I and III caused intestinal damage. Immunologically, genotypes I and IV triggered strong early pro-inflammatory cytokine responses and significantly upregulated MMP13 and Wnt14 at 7 dpi. This points to severe immune activation and a high risk of joint injury. These distinct biological and pathogenic profiles among the tested ARV strains underscore the need for genotype-specific vaccine strategies.