Preliminary Evaluation On The Efficacy Of Inactivated Duck Hemorrhagic Ovaritis Vaccine

Vaccine immunization is the most effective method to prevent epidemic diseases, and there is no commercialized DHO vaccine temporarily. The vaccine is still developing and researching at present. Efficiency is one of the most important indicators of vaccine quality. The purpose of this study is to control the quality of the inactivated vaccine, by establishing a feasible evaluation method using a variety of experimental methods on the inactivated DHO vaccine.30 immunized laying ducks (immunized group) and 5 non-immunized laying ducks (control group) were artificially infected with DHOV after second immunization with two batches of lab preproduction vaccine (A and B).Serum samples were collected for virus-isolation by inoculation into SPF chicken embryos on 5 DPI, and the status of embryos were observed during 24-168h after inoculation. The PD50 of different batches of vaccines were calculated by Reed-Muench. Another 10 immunized with A and B ducks (immunized group) and 5 ducks (control group) were chose to collected serum samples for determining biochemical indexes at the day before challenging and 2 DPI separately. The ducks were necropsied at day 7 after infection and gross lesions were examined, and the solid organs were fixed in formalin to make pathological tissue section for histologic observation and immunohistochemical detection.The PD50 of different batches of vaccines were determined, which were 11.84 (A) and 6.34 (B), respectively. The Serum Biochemical Indexes(ALT、AST、TBIL) content levels of challenged ducks (control group) did make significant difference at the day before inoculation and 2 days post infection, while the ducks of immunized group did not. Histopathological examination showed that ovarian hemorrhage, deformations, theca of hemorrhage and congestion; splenomegaly obviously granophyric textures on the surface appear white pulp lymphocyte loss disintegration, reticular cells hyperplasia; turn yellow and brittle texture of the liver, fatty degeneration of liver cells and perivascular lymphocytic infiltrates; the phenomenon of neuronphage and other histopathological changes were observed in brain tissue. Immunohistochemical results showed that a large amount of positive granules were found in the cytoplasm of the heart, liver, spleen, kidneys, brain,and ovarian tissue of the ducks of control group, and individual organs of the ducks in immunized group were also found but significantly less than the control group. The results of comparison between two batches of vaccines showed that the positive granules in the tissue cytoplasm of ducks immunized B vaccine were more obvious compared to the group A.It was indicated that two batches of Inactivated Duck Hemorrhagic Ovaritis Vaccine were effective by preliminary evaluation with median protective dose (PD50), serum biochemical indices and histopathological examination.