Comparative efficacy of commercial Porcine Circovirus Vaccines against Heterologous Genotype infection

Abstract

The twenty-four crossbred male pigs at 26 days of age with high maternally derived antibody were divided into 4 groups, negative control group, chimeric PCV type1-type2a (PCV2a) antigen based vaccine group, chimeric PCV type1-type2a and 2b (PCV2a-2b) antigen based vaccine group and positive control group. Three weeks after vaccination, all pigs except negative control group were inoculated with PCV2d (PCV2d/149/TH/2020) at 105 50% tissue culture infectious dose (TCID50) per mL 4 mL/pig, divided into 2 routes of inoculation including intranasal and intramuscular 2 mL/route. Every week except the day of vaccination, blood samples were collected from each pig for PCV2 neutralizing antibody titers measurement by IPMA, PCV2-specific immunoglobulin G antibody (IgG) titers evaluation by ELISA, PCV2 DNA detection by real time PCR. The initial weight and final weight were measured at the day of arrival and 28 days after inoculation or 75 days old. At 77 days old, all pigs were euthanized. Macroscopic and microscopic examination from lung tissues, superficial inguinal lymph nodes, tracheobronchial lymph node and mesenteric lymph nodes were evaluated at the end of the study and immunohistochemistry (IHC) staining were used for PCV2 viral antigen detection. The result indicated that in the heterologous genotype inoculation, chimeric PCV type1-type2a and 2b (PCV2a-2b) antigen based vaccine induced higher PCV2 specific neutralizing antibody titers significantly compared to chimeric PCV type1-type2a (PCV2a) antigen based vaccine. Moreover, chimeric PCV type1-type2a and 2b (PCV2a-2b) antigen based vaccine could be used to reduce the incidence of infection in lymphoid tissues evaluated by immunohistochemistry score. However, both types of PCV2 vaccines could be used to stimulate the immunological response before infection and delay the presence of viremia.