Comparative efficacy of experimental inactivated and live-attenuated chimeric porcine circovirus (PCV) 1-2b vaccines derived from PCV1 and PCV2b isolates originated in China.

BACKGROUND: Porcine circovirus type-2b (PCV2b) is recognized as the etiological agent of the various clinical manifestations of porcine circovirus-associated disease (PCVAD). Previous studies have demonstrated effectiveness of chimeric PCV1-2 vaccines against PCV2b challenge. In this study, the efficacy of inactivated and live-attenuated (2 × 10(3.5) or 2 × 10(4.0) 50% tissue culture infective dose [TCID50] dose) chimeric PCV1-2b vaccines was compared side-by-side in conventional pigs. METHODS: Twenty-seven non-PCV2 viremic pigs without PCV2-specific antibody were randomly divided into six groups, including four vaccinated and challenged groups, a nonvaccinated challenged group, and a mock group. All pigs except those in the mock group were challenged at 28 days post vaccination (DPV) using PCV2b. RESULTS: Both inactivated and live-attenuated chimeric PCV1-2b vaccines induced a robust antibody responses, and significantly decreased microscopic lesion and lower viral loads in serum or superficial inguinal lymph nodes (SILN) compared with that in the nonvaccinated challenged group. PCV2 antibody titers decreased after 7 days post challenge (DPC) in pigs administered the inactivated PCV1-2b vaccine and they were lower than those in pigs inoculated with live-attenuated PCV1-2b on the day of necropsy. Moreover, no viremia was present in pigs inoculated with live-attenuated PCV1-2b vaccine at 21 DPC regardless of the dose difference. CONCLUSIONS: The results demonstrated that both inactivated and live-attenuated chimeric PCV1-2b vaccines were effective to induce protective immunity against PCV2b infection.