Pathogenicity of Muscovy Duck Reovirus Isolate B3

The general haemorrahage and gray_white necrotic foci were observed on the surface of liver and spleen of the dead embryos of muscovy ducks,hybrid(muscovy)ducks or chickens inoculated with the muscovy duck reovirus isolate B3.The infected liver cells of muscovy duck showed the granular degeneration,and then lysis,The experiments confirmed that the isolate B3 could be transmitted through infected eggs or by nasal,oral,intramuscular(i.m.),pad injection and co_breeding.The incubation period of one_day_old muscovy ducks inoculated with isolate B3 was from 3 to 11 days,the rate of mortality was up to 100%,but some resistance to the isolate B3 were found in the one_day_old hybrid(Muscovy)ducks or chickens.There were inflammatory responses caused by the pad inoculation to the muscovy ducks,hybrid(muscovy)ducks or chickens of one_day_old,though the apparent clinical signs didn′t happen by i.m.injection on hybrid(Muscovy)ducks or chickens.Macroscopically,fibrinous pericarditis,gray_white necrotic foci,enlarged friable liver,and marbled spleen were seen in dead muscovy ducks infected with the isolate B3.Microscopical observation found that there were focal necroses in liver,spleen,cardiac muscle(heart),kidney,bursa,proventriculus and intestinal submucosal coat,and they were especially appatent in liver and spleen,and the tissue structure of splenic white pulp and liver was destroyed.Lymphocytic and phagocytic infiltrations were consistently found in the perivascular of the liver and brain,and in the interstice of cardiac muscle,kidney and lung.The lymphocytic degenerations and necroses were also seen in the bursa of Fabricius.EM examinations revealed that there were virus_like particles and inclusion bodies near the nucleus;multinuclear,vacuollization and granular degeneration were found in the liver cells and the lymphocytes of spleen of infected embryos.The isolate B3 also resulted in apoptosis,virus_like particles and apoptic bodies in the cytoplasm of phagocytes.The findings were firstly reported so far in china.