Orthoreovirus avis in asymptomatic broiler chickens.

Orthoreovirus avis (previously named Avian othoreoviruses; ARVs) cause significant economic losses in the global poultry industry. Disease control is compromised by the emergence of variants that escape vaccine-induced immunity. The development of more effective vaccines requires knowledge of circulating strains. One hundred and twenty-four feces from asymptomatic and unvaccinated broiler chickens from two commercial poultry farms in the states of Rio de Janeiro and Espírito Santo, southeastern Brazil, were examined with the aim of detecting, genotyping and characterizing the σC protein of the circulating strains. ARV was detected in both flocks 39 (31.5%; n = 124) samples: 23 from Rio de Janeiro and 16 from Espírito Santo. Phylogenetic analysis demonstrated the circulation of strains belonging to genotypes I, III, and IV (GI, GIII and GIV, respectively). Pairwise comparisons of the σC amino acid sequences showed that the GI strain (BJ12), shared the highest sequence identity (97.1–99.4% identity) with other Brazilian GI strains detected in diseased birds and 76.5–77.6 the reference vaccine strains. The GIII strains presented identity percentages of 90.6–100% among themselves, 91.2–94.1% with the Brazilian GIII strain BR5881 detected in symptomatic birds and 59.4–74.1% with other GIII reference strains. The GIV strain (MF111) showed identity of 79.5–80.6 with reference strains of the same genotype. These findings indicate the co-circulation of multiple ARV genotypes that may facilitate reassortment and consequent emergence of new pathogenic variants. Consequently, continuous epidemiologic surveillance of avian reoviruses is necessary, particularly in regions where poultry farming is practiced at an industrial scale.