Genotypic characterization of two novel avian orthoreoviruses isolated in Iran from broilers with viral arthritis and malabsorption syndrome.

Background: Avian reovirus (ARV) is a major poultry pathogen associated with arthritis, malabsorption, and enteric diseases in chickens. In recent years, emerging ARV strains have become a growing concern causing significant economic losses in broiler chickens around the world. This report focuses on the isolation of ARV from the clinical occurrence of ARV-associated diseases in commercial broiler chickens in Iran and the genotypic characterization of the selected isolates. Case description: In 2018, two distinct clinical diseases, suggestive of malabsorption syndrome (MAS) and viral arthritis, were noticed in commercial broiler chickens in the north of Iran. Laboratory investigations were carried out following necropsy, documentation of the gross lesions, and sampling of the affected tissues for histopathology and virology. Molecular diagnosis and characterization of ARV were performed targeting Sigma C (σC) gene sequences of the virus. Findings/treatment and outcome: Two variant ARV strains were isolated from tendon and gizzard of broilers with clinical viral arthritis and MAS, respectively. Phylogenetic analysis of the ARV σC gene sequences revealed that field isolates were clustered in genotypes 2 and 4 (which were distinct from previous Iranian field ARV strains) with relatively low sequence identity (59.2% and 49.1%) to the classical vaccine strains (S1133 and 1733) in genotype 1. This report, for the first time, represents new emerging ARV variants associated with clinical events in Iran, providing insights on the diversity of endemic ARV field isolates, and urges the need for national-wide surveillance of ARV.