Emerging Forms of Avian Orthoreovirus Infection in Turkeys in Québec, Canada, Associated with Tenosynovitis,...

New avian orthoreovirus strains have emerged in commercial turkey in North America since 2011, mostly characterized by tenosynovitis and rarely with a necrotizing hepatitis in younger birds. In 2020, orthoreovirus infections were diagnosed in turkey flocks for the first time in Québec, leading to significant economic losses in young poults and in older turkeys. At necropsy, older birds had a lymphoplasmacytic tenosynovitis occasionally associated with aortic rupture. In younger poults, the lesions were mostly characterized by hepatocellular necrotic foci and degenerated syncytial hepatocytes. Some 31- and 69-day-old poults displayed ataxia and tremors and had a nonsuppurative encephalitis affecting the cerebellum and pons. A novel immunohistochemistry protocol successfully demonstrated the presence of the virus within the lungs, liver, and spleen lesions of birds with hepatitis. Those poults with hepatitis had the highest viral load (reverse transcriptase quantitative PCR [RT-qPCR] average cycle threshold [Ct] value of 11.56 ± 2.16) compared to tenosynovitis (23.54 ± 3.77) and encephalitis cases (22.4 and 33.1; P < 0.0001). Whole-genome sequences (WGS) of all reoviral RNA segments (n = 10) were obtained from 14 turkey orthoreovirus isolates, including 1 isolate linked to encephalitis. Overall, at least four different strains were identified according to their reassortment profile (RP), illustrating the high genomic variability of the virus. However, no RP could be associated to a specific viral pathotype. In conclusion, different avian orthoreovirus strains are spreading in turkey flocks in North America, associated with multiple disease syndromes, such as tenosynovitis, hepatitis, and encephalitis.