Coinfection Of Goose Parvovirus And Duck Circovirus Enhances The Pathogenicity In Ducks

Goose parvovirus(GPV)is the pathogen of gosling plague.In recent years,GPV infection has been detected in the diseased ducks with beak atrophy and dwarfism syndrome(BADS)in China.Duck circovirus(DuCV)can lead to host immunosuppression,and co-infection with other pathogens complicates disease progression.Co-infection of GPV and DuCV was widespread in the field,but the pathogenicity of co-infection of GPV and DuCV was not clear at present.To investigate the pathogenicity of co-infection of GPV and DuCV,GPV and DuCV were isolated,and an animal model of co-infection of GPV and DuCV was established in this study.We isolated GPV and DuCV and prepared GPV polyclonal antibody and DuCV polyclonal antibody for experimental detection.GPV and DuCV were intraperitoneally inoculated in 2-day-old cherry valley ducks,which were killed on the 10 th,20th and 30 th days post infection.The clinical manifestations of co-infection of GPV and DuCV in ducks were depression,growth retardation,and messy feathers.The body weight of the co-infection group increased slowly and was significantly lower than that of the single-infection group and the normal group.Blood smears revealed large numbers of heterotrophic granulocytes and lymphocytes in the blood.The serum enzyme activity was detected,and it was found that the ALT level in the co-infection group was significantly higher than that in the single-infection group and the normal group,reflecting the aggravation of liver damage caused by the co-infection of GPV and DuCV.The gross lesions in the co-infection group were liver hemorrhage and necrosis,spleen atrophy and paleness,thymus and bursa of fabricius atrophy and marrow paleness.In histopathological changes,the lesions of the immune tissues and organs were the most typical.In the spleen,lymphocyte loss,hemorrhage,and heterophilic granulocyte infiltration occur,and the red and white pulp boundaries of the spleen disappear.Thymic lymphocyte loss,large amount of heterophilic granulocyte infiltration and thymic body disintegration were observed in thymus.Lymphocyte loss in bursa of fabricius and massive loss of hematopoietic cells from bone marrow can be observed.In the digestive organs,the duodenal villi showed necrosis and exfoliation.In the metabolic organs,liver hassevere vacuolar degeneration with inflammatory foci and infiltrates.Renal tubular cell vacuolar degeneration,necrosis and shedding,hemorrhage occurred in the kidney.Through the detection of the dynamic changes of viral load in different tissues at each time point,we found that the viral load in the co-infection group was significantly lower than that in the single-infection group at the initial stage of infection,but with the development of the course of disease,the viral load in the single-infection group decreased,and the replication of GPV and DuCV in the co-infected animals were both higher than that in the single-infected group.The distribution and localization of GPV and DuCV in vivo were detected by IHC,and positive cells were detected in liver,spleen,kidney,duodenum and bursa of fabricius.With the increase of age,the number and signal intensity of positive cells in the co-infection group were higher than those in the single-infection group,and the distribution and localization of the two viruses were basically the same.At the initial stage of infection,both viruses were located in the liver nucleus,and positive signals could be detected in the cytoplasm and nucleus of liver cells after 30 days of infection.Positive cells can be detected in renal tubules in the medullary loops of the kidney.In the early stage of infection,the positive cells in the duodenum were mainly in the cryptic fossa,and later in the goblet cells of the intestinal villi of the duodenum.DuCV positive cells in the bursa of fabricius were mainly distributed in the medulla,while GPV positive cells were detected in both cortex and medulla.The above results showed that the co-infection of GPV and DuCV could synergistically promote the pathogenicity and virus replication of the two viruses respectively,thus aggravating the disease of the infected duck.This study revealed the synergistic pathogenic effect of GPV and DuCV co-infection in terms of pathogenicity and virus replication,which not only clarified the direction of the subsequent study on the mechanism of GPV and DuCV co-infection,but also provided scientific theoretical basis for the study of immunosuppressive disease or other poultry diseases.