Serologic and Pathogenetic Studies on Avian Reoviruses Isolated in Japan

SUMMARY. Eighty-nine avian reoviruses isolated from diseased and clinically normal chickens were classified serologically using antisera against five prototype strains. Eighty-three strains were classified into five serotypes; six strains were untypable. Most of the cytopathogenic strains that produced a clear cytopathic effect (CPE) in chicken embryo fibroblasts (CEFs) were highly pathogenic for chicken embryos (80% or more mortality via the allantoic sac) and for chicks (severe footpad swellings and tenosynovitis). These strains were classified into a single serotype represented by the TS-142 prototype strain. However, 10 strains that could not produce a clear CPE in CEFs showed very low pathogenicity for embryos and chicks, and these strains were serologically different from the TS-142 prototype strain. There was a strong relationship between pathogenicity and serotype. About 17% of the isolates were considered highly pathogenic.