Study On The Inactivated Vaccine Against Porcine Circovirus Type2 (WH Strain) Infection

Porcine circovirus type 2 ( PCV2) infection is recognized as the major factor in the development of post-weaning multisystemic wasting syndrome (PMWS),although other factors may enhance the severity of the disease. At present, PCV2 is widely spreaded in the world and maintain high infection rate in herd. Vaccine inoculation is the main method to prevent and control PCV2 infection; however, there is no commercial vaccine against PCV2 in China yet.An inactivated vaccine was developed based on porcine circovirus type 2 WH strains, a wild strain separated in pig farm Wuhan. To fight against porcine circovirus type 2, the following works were performed aiming to prepare a novel vaccine.1. Development of inactivated vaccine against porcine circovirus type 2PCV-2 WH strain was inoculated into PK-15 cell by the way of one-stepinoculation. After forming a single layer, the cells were treated with 300mmol/L D-glucosamine, at 37℃for 30min, discarded the D-glucosamine, then added DMEM with 2% newborn bovine serum and cultured for another 48h, harvesting virus. PCV2 was inactivated with 0.3% formalin. The inactivated vaccine was prepared with inactivated virus and appropriate amount of American oil-adjuvant.Then sterility and physical character of the vaccine was detected.2. Determination of minimum immune dosage of the inactivated vaccinePiglets immunized with 10^5.0TCID₅₀,10^6.0TCID₅₀ and 10^7.0TCID₅₀ antigen doserespectively, then the immune efficacies of the vaccines against PCV2 were evaluated by ELISA antibody detection, clinical signs (fever), viremia and distribution of viral DNA in different tissues. Further Piglets were immunized with minimum immune dosage by 1ml, 2ml and 3ml, respectively, and then the im mune efficacy was evaluated according to the method mentioned above. The results were as follows:â‘ The efficient immune response could be induced with the vaccine of 10^7.0 TCID₅₀ PCV2 in piglets, while specific antibody wasn't detected with the vaccine of 10^6.0 TCID₅₀PCV2 and 10^5.0 TCID₅₀ PCV2 in piglets.â‘¡High ELISA antibody titers of the vaccines with 10^7.0 TCID₅₀ 1ml,2 ml and 3ml could be detected in piglets. The immune efficacy of 10^7.0 TCID₅₀ PCV2 2ml was obviously higher than the other 2 groups.â‘¢After PCV2 challenge the rectal temperature of all piglets were recorded. Average temperature of piglets in challenge control group was higher than that of immunized piglets. The fact that vaccines could reduce the persistence of PCV2 in piglets was indicated by detection of viremia and PCV2 in different tissues of challenged piglets. The immune efficacy of 10^7.0TCID₅₀PCV2 2ml dosage group was the best in all groups.3. Evaluation of the efficacy of the inactivated vaccineAfter piglets immunized with vaccine 2ml for one week, two weeks, three weeks and four weeks respectively, the immune efficacies of the vaccines against PCV2 were evaluated by clinical signs (fever), viremia and distribution of viral DNA in the tissues. The results showed that challenge with porcine circovirus type 2 strains WH after post immunized for one week and two weeks, there was no difference between the control group and the immunized group. Challenge with porcine circovirus type 2 strains WH after post immunized for three weeks and four weeks, viremia and viral DNA in the tissues were detected in two piglets of the immunized group, while viremia and viral DNA in the tissues were detected in five piglets of the control group. It could be concluded that the inactivated vaccine could protect piglets from PCV2 infection after immunized for three weeks.4. Evaluation of the safety of the inactivated vaccinePiglets were inoculated with single dose and double doses of the inactivated vaccine and the rectal temperature of all piglets were recorded before and after inoculation. Then clinical symptoms such as appetite were observed. 28 days after inoculated, the situation of the vaccine absorption was observed. According to clinical symptoms, there was no significant difference between before and after inoculation. After autopsy, there was no residual vaccine in the injection site. Both single dose and double dose of the vaccine are safe to the piglets. It could be concluded that the inactivated vaccine is safe in piglets.