Reoviral Hepatitis in Young Turkey Poults-An Emerging Problem

From January 2019 to April 2020, the Minnesota Veterinary Diagnostic Laboratory (MVDL) received cases of hepatitis and spiking mortality in young turkey poults (average age 15.5 days) from multiple turkey-producing states. Meat-type turkeys were mainly affected, with a few cases in breeders. Of 188 cases, 88 (47.5%) tested positive for reovirus by virus isolation, with most of the positive cases from 7 to 14-day-old birds (n = 42). Gross lesions consisted of hepatosplenomegaly with acute, multifocal necrosis in both liver and spleen. Microscopically, liver sections showed congestion of hepatic sinusoids and necrotizing hepatitis with infiltration of lymphocytes, plasma cells, and macrophages. Reovirus was detected in liver samples by electron microscopy and in situ hybridization (ISH). Sections of spleen showed areas of necrosis with infiltration of the mixed population of inflammatory cells and depletion of lymphocytes. We consistently isolated reoviruses from livers and tentatively named the virus "Turkey Hepatitis Reovirus" (THRV). Phylogenetic analysis of the newly emerged THRVs revealed their clustering into four distinct groups. This study also highlighted the close antigenic relation between TARV and THRV compared to turkey enteritis reoviruses (TERVs), which shed light on the probable origin of this newly emerged pathotype. In summary, further molecular and pathogenicity studies are recommended on THRVs to help diagnose and control this serious variant.