Genetic and pathogenic characteristics of two novel/recombinant avian orthoreovirus

In recent years, the emerging avian orthoreovirus (ARV) strains that led to viral arthritis have attracted much attention from the chicken industry worldwide, due to the significant economic losses suffered. In mid-2020, with the assistance of next-generation sequencing technology, we achieved success in characterizing two divergent avian orthoreovirus (ARV) variants (0543/SDYT) and isolating them from the broiler tendons characterized by arthritis. As suggested by the genome characterization of the 0543/SDYT strains, they belong separately to clusters Ⅰ and Ⅳ. As revealed by sequence comparison, phylogenetic, and recombination analysis, for μA, μB, and σNS genes, considerable genetic divergences were also observed in the two new isolates. However, in the case of λA, λB, μNS, σA, and σB genes, very clear clustering patterns were observed for SDYT and 0543 field strains, respectively. In terms of the μA, μNS, p10, p17 genes of SDYT isolate and μNS, p17, σC, σA genes of 0543 isolate, the lower similarity was observed with NCBI stored sequences, with nt highest identity values below 90 %. In addition, there is an intra-fragmental recombination event in the M1 gene of the SDYT strain. In regard, the multiple segmental recombination and accumulation of point mutations play a role in the newly-emerging ARV strains. Not only did the isolates strain exhibit strong replication ability in vivo, but they also displayed strong arthritogenicity in broilers with low neutralizing maternal antibodies, indicating that maternal antibody treatment may not effectively reduce the oral infection of avian orthoreovirus. These findings suggest that it is necessary to develop a new strategy for enhanced effectiveness in preventing and controlling ARV infection.