Phylogenetic Analysis and Pathogenicity of Avian Reoviruses Isolated from Viral Arthritis Cases in China 2010-2024

Avian reovirus (ARV) is one of the main causes of viral arthritis, tenosynovitis, malabsorption syndrome (MAS), runting-stunting syndrome, and immunodepression. In recent years, due to the emergence of new ARV strains, outbreaks of the disease have brought significant economic losses to chicken flocks. To determine the prevalence of ARV in China from 2010 to 2024, a total of 409 tissue samples from different breeding farms were collected from chickens presenting clinical signs of lameness and swollen joints in various flocks located in 18 provinces. As performed on these tissue samples, the ARV-specific reverse transcription-polymerase chain reaction (RT-PCR) assay indicated 111 ARV-positive samples with a positive rate of 27.14%. After viral isolation from the necropsied chicken samples, 69 ARV strains were isolated, and specific sigma C (σC) genes were amplified and sequenced. The sequence analysis of σC genes showed that these 69 isolates were grouped into six clusters, including 14 ARV isolates from cluster I (20.29%), 12 ARV isolates from cluster II (17.39%), 3 ARV isolates from cluster III (4.35%), 8 ARV isolates from cluster IV (11.59%), 3 ARV isolates from cluster V (4.35%), and 29 ARV isolates from cluster VI (42.03%). Except for cluster V, each of the other five clusters could be divided into two subclusters. Homology analysis showed that ARV isolates in clusters II-VI had only 50.3 to 60.8% homology with the commercial S1133 vaccine strain which is derived from cluster I. The ARVs in subcluster Ia had high homology with the S1133 vaccine strain (93.5-98.0%), while the ARVs in subcluster Ib had a low homology with the S1133 strain (73.4-76.4%). Further, the cluster VI viruses, the main epidemic genotype in China, had only 50.3-55.7% homology with the S1133 strain. The results of the pathogenicity test showed that the representative strains of the six different clusters all caused swelling of the footpads in SPF chickens, and the incidence rate was not significantly different. The present study will be helpful in the understanding the prevalence of ARV strains in China and revealed the genetic differences between the ARV isolates and the commercial vaccine strain.