Effect Of Experimental Infection With PCV2 On Lymphoid Tissues And Study On The Inactivated Vaccine Against PCV2 (WH Strain) Infection

Porcine Circovirus Disease (PCVD) caused by porcine circovirus type 2 (PCV2) is an important pathogen of swine following porcine reproductive and respiratory syndrome (PRRS). Porcine circovirus type 2 (PCV2) is considered to be the necessary cause of post-weaning multisystemic syndrome (PMWS), besides, it is also related to reproductive failure, porcine dermatopathy and nephropathy syndrome (PDNS), porcine respiratory disease complex (PRDC) and CT et.al. The occurrence and spread of the disease has caused considerable economic losses to the world's pig industry. In China the pig industry is well developing, however, no commercial vaccine has been used so far. So the objective of this study was to provide a basis for the immune efficacies of the vaccines against PCV2 (WH Strain) by histopathological and immunohistochemical studies. Histopathological studies were done to evaluate the apparent degree of lymphocyte depletion and infiltration with macrophages and immunohistochemical studies were done to determine the viral load of PCV2 in different lymphoid organs between the control group and the immunized group. Main research and findings include the following:1 Histopathological findings and distribution of PCV2 antigen in lymphoid organs after immunized with different antigen dosesIn this experiment, twenty 25-35 day old piglets were randomly assigned to 4 groups. One group was not immunized as control group, and the other three groups were immunized with 105.0TCID50,106.0TCID50 and 107.0TCID50 antigen dose respectively. After challenged with porcine circovirus type 2 strains WH for 28 days, the piglets were sacrificed and spleens, lymph nodes, tonsils were collected. The histopathologcial results showed that the piglets in control group had severe lymphoid depletion and infiltration with macrophages in lymphoid nodes and tonsils, and moderate lymphoid depletion and infiltration with macrophages in spleens. The piglets in immunized group (107.0TCID50) had mild lesions in lymphoid tissues. The IHC results showed that infectious cells are mainly in the cytoplasm in macrophages. There were more infectious cells in control(challenge) group than immunized group in spleens, lymph nodes and tonsils. The infectious cells were least in immunized group(107.0TCID5o) in spleens, lymph nodes and tonsils. There was significant difference beween control(challenge) group and immunized group. However, there was no significant difference among immunized groups(105.0TCID50,106.0TCID50) 107.0TCID50). These results suggested that the vaccines against PCV2 (WH Strain) had a certain protective effect and vaccine with 107.0TCID50 antigen dose had a better immune efficacies.2 Histopathological findings and distribution of PCV2 antigen in lymphoid organs after immunized in different timeIn this experiment, forty 25-35 day old piglets were randomly assigned to 8 groups. Four groups were not immunized as control group, and the other four groups were immunized with vaccine 2ml for one week, two weeks, three weeks and four weeks respectively. After challenged with porcine circovirus type 2 strains WH for 28days, the piglets were sacrificed and spleens, lymph nodes, tonsils were collected. The results showed that the piglets in control group had severe lymphoid depletion and infiltration with macrophages in lymphoid nodes, spleens and tonsils. The piglets immunized for 1w,2w,3w had moderate lesions and for 4w had mild lesions in lymphoid nodes and spleens. The piglets immunized for 1w,2w had moderate lesions and for 3w,4w had mild lesions in tonsils. The piglets immunized for 4w had mild lesions in lymphoid tissues. The IHC results showed that infectious cells were mainly in the cytoplasm in moncytes/macrophages. Compared to control(challenge) group, the infectious cells in immunized group were decreased. There was significant difference beween control(challenge) group and immunized group. The infectious cells were least in the group immunized for 4w. These results suggested that the vaccines against PCV2 (WH Strain) had a certain protective effect and had a better immune efficacies after immunized for 4w.