An experimental live chimeric porcine circovirus 1‐2a vaccine decreases porcine circovirus 2b viremia when administered intramuscularly or orally in a porcine circovirus 2b and porcine reproductive and respiratory syndrome virus dual‐challenge model

ABSTRACT Commercially available inactivated vaccines against porcine circovirus type 2 (PCV2) have been shown to be effective in reducing PCV2 viremia. Live‐attenuated, orally administered vaccines are widely used in the swine industry for several pathogens because of their ease of use yet they are not currently available for PCV2 and efficacy. The aims of this study were to determine the efficacy of a live‐attenuated chimeric PCV2 vaccine in a dual‐challenge model using PCV2b and porcine reproductive and respiratory syndrome virus (PRRSV) and to compare intramuscular (IM) and oral (PO) routes of vaccination. Eighty‐three 2‐week‐old pigs were randomized into 12 treatment groups: four vaccinated IM, four vaccinated PO and four non‐vaccinated (control) groups. Vaccination was performed at 3 weeks of age using a PCV1‐2a live‐attenuated vaccine followed by no challenge, or challenge with PCV2b, PRRSV or a combination of PCV2b and PRRSV at 7 weeks of age. IM administration of the vaccine elicited an anti‐PCV2 antibody response between 14 and 28 days post vaccination, 21/28 of the pigs being seropositive prior to challenge. In contrast, the anti‐PCV2 antibody response in PO vaccinated pigs was delayed, only 1/27 of the pigs being seropositive at challenge. At 21 days post challenge, PCV2 DNA loads were reduced by 80.4% in the IM vaccinated groups and by 29.6% in the PO vaccinated groups. PCV1‐2a (vaccine) viremia was not identified in any of the pigs. Under the conditions of this study, the live attenuated PCV1‐2a vaccine was safe and provided immune protection resulting in reduction of viremia. The IM route provided the most effective protection.