The first complete genome sequence and pathogenicity characterization of a reassortant avian orthoreovirus genotype Ⅰ subvariant strain

Avian orthoreovirus (ARV) is an important pathogen responsible for viral arthritis in poultry, causing significant economic losses to the poultry industry. In this study, an ARV strain designated QD25 was isolated from 28-day-old commercial broilers with tarsal joint swelling and paralysis in Shandong Province. The complete genome of QD25 was sequenced to enable comprehensive molecular characterization. Phylogenetic analysis based on the σC-encoding gene classified QD25 within genotype I subvariant, with 88.9–89.6% homology to strain ISR5225 and only 73.3% homology to vaccine strain S1133. Notably, phylogenetic analysis of the σNS non-structural protein encoded by the S4 segment positioned QD25 within the same clade as genotype III strains, suggesting that this strain has undergone a typical inter-genotype reassortment event involving σNS. Pathogenicity tests revealed that QD25 caused 40% mortality and significant growth suppression in specific pathogen-free chickens with severe histopathological lesions in multiple tissues. These results highlight the evolutionary features of ARV genetic reassortment. Moreover, the complete genome data offer robust evidence for strain tracing, molecular subtyping, and epidemiological monitoring, while also providing a theoretical basis for the rational prevention and control of ARV.