Pathogenicity of duck avian reovirus for Pekin ducklings

Fifteen ducklings for the experiment were inoculated with duck avian reovirus(DRV)SDWF strain with 0.2mL of the undiluted infective amnio-allantoic fluids(ELD50=10-2.36/0.2mL)which was isolated from duck through intravenous injection at 10-day-old.At the same time,fifteen ducklings were inoculated with sterile physiological saline in the same way as control group.Ducklings were regularly observed for clinical signs,and the following procedures were conducted for each group at 3,6,9,12 and 15days post inoculation.Blood was collected from three ducklings randomly selected from each group and the ratio of CD4+/CD8+was examined by flow cytometry.The serum was collected to examine IL-6and IFN-γlevels by ELISA kits,respectively.Moreover,necropsy lesions and histopathological changes were observed.Additionally,whole body weight,relative weights of immune organs,such as spleen,thymus and bursa were also investigated at 3,6,9,12 and 15days post inoculation.Results showed that all of 15 ducklings inoculated with reovirus showed depression and loss of appetite at 3days post inoculation.Ducklings appeared smaller than the control group.The pathohistology changes of ducklings after anatomy included spleen enlarged,haemorrhages,necrosis and more visible yellow focal necrosis were observed in liver.Histopathological results showed that the immune organs such as bursa and spleen performed significantly microscopic changes.Lymphocyte depletion was evident with reticular fiber visualized in bursa and spleen.The granuloma structure and necrotic foci were seen in the spleen and the artery of spleen showed homogenizing,swollen,sparsely,vacuolar degeneration in vessel wall,even occlusive.Indirectly flow cytometry results showed that the ratios of CD4+/CD8+increased at 3days post inoculation,then significantly decreased compared with controls at6,9days post inoculation.Although it increased later,the ratio of CD4+/CD8+still remained lower than that of control group.The regularity of IL-6and IFN-γshowed as same as CD4+/CD8+and were significantly lower than those of control group at 9days post inoculation.Results of immune organ indexes showed that thymus and bursa indexes were significantly lower than control group at 6days post inoculation.However,altered spleen index were always larger than those of uninfected.In conclusion,immune organs such as spleen and bursa were the objective organs after infected with reovirus,and the serious depletion of immune organ lymphocyte leaded to the body immune suppression.