Anatomopathological and molecular characterization of avian reovirus in broilers condemned due to arthritis in Southern Brazil

Condemnations in slaughterhouses are a recurring cause of losses for the poultry industry. This study aimed to evaluate the involvement of avian reovirus (ARV) in arthritis-related condemnations in a broiler slaughterhouse under Brazilian Federal Inspection. A total of 150 pelvic limbs condemned for arthritis were collected from the inspection line at the time of condemnation, originating from 30 flocks not vaccinated against ARV. For the detection of ARV, real-time polymerase chain reaction following reverse transcription (RT-qPCR) was performed on a pool of five gastrocnemius tendons from each flock using the primers ReoS-F1, ReoS-R1, ReoS-F2, and ReoS-R2, followed by Sanger sequencing of the σC gene. For macroscopic and histopathological analyses, the gastrocnemius, digital flexor, and extensor tendons, as well as the articular cartilage of the tibiotarsometatarsal joint, were evaluated. Injuries were classified into four degrees, ranging from G0 (no changes) to G3 (highest degree of injury). Macroscopic injury scores revealed a higher percentage of injuries in the gastrocnemius tendon compared to the extensor and flexor tendons. Histological changes were observed in the peritendon and muscles adjacent to the tendons, including infiltration of heterophils, macrophages, lymphocytes, plasma cells with lymphoid aggregates, haemorrhage, and fibrinous exudate in the gastrocnemius, flexor, and digital extensor tendons. ARV was detected in 50% of the flocks by RT-qPCR, with no correlation to increased arthritis condemnations (<i>P</i> > 0.05). The sequence analysis identified the cluster as lineage VI, a strain not present in Brazil's commercial vaccination programmes. The study concludes that half of the investigated flocks were positive for ARV, identifying a cluster absent in current Brazilian vaccination programmes.