Genetic and Pathogenic Characteristics of Variant Avian Reovirus Strains Isolated from Diseased Chickens in China

Avian viral arthritis (AVA), caused by avian reovirus (ARV), is a viral disease in chickens that has led to significant economic losses in the poultry industry. Recent studies have shown that traditional ARV vaccines based on the S1133 strain fail to protect against emerging ARV variants. In this study, we isolated and characterized three ARV strains (G4, YV, WF) from immunized chicken flocks with respiratory and arthritic symptoms. Genomic analysis revealed that the σC genes of G4, YV, and WF shared only 55.5%, 55.7%, and 58.7% sequence homology, respectively, with the S1133 strain. Phylogenetic analysis placed them in different branches, indicating they are variant strains. YV and WF belong to genotype III, and G4 falls into genotype VI. Whole genome analysis revealed gene segment reassortment among the variants. Pathogenicity testing in three-week-old SPF chickens showed that G4 (genotype VI) caused swelling of footpads, whereas WF (genotype III) did not. G4-infected chickens exhibited significantly higher viral loads in the thymus, lungs, spleen, and bursa of Fabricius than those in the WF-infected chickens, indicating viruses from different genotypes showed various pathogenesis. These results suggested an urgent need for new updates of vaccines against the variant ARVs, especially the genotype VI virus.