Induction of humoral immune response in piglets after perinatal or post-weaning immunization against porcine circovirus type-2 or keyhole limpet hemocyanin.

The objective of this study was to test the hypothesis that porcine circovirus type-2 (PCV2) vaccination is efficacious when administered in the first week of life. Three groups of pigs were vaccinated with Circumvent either early (at the end of week 1), late (at the end of week 4), or not at all. All 3 groups were later challenged intranasally with PCV2 (at the end of week 5). Two other groups were immunized with keyhole limpet hemocyanin (KLH) as a novel antigen at the end of either week 1 or week 4. Weight, PCV2 genome copy number in serum and saliva, anti-KLH antibody titer, and serum PCV2-neutralizing antibodies were measured weekly. Early PCV2 vaccination or KLH antigen exposure resulted in earlier humoral responses that were slower to develop than in older piglets, yet converged with the responses to later vaccination within 5 wk. Both groups of vaccinated piglets had periods of higher PCV2-neutralizing antibody titers and lower viral levels shortly after weaning and PCV2 challenge, thus supporting the recent labelling of 1 Canadian PCV2 vaccine for use in week 1 and suggesting that early PCV2 vaccination can reduce piglet handling without compromising vaccine efficacy.