Effect of porcine circovirus type 2 (PCV2) vaccination on PCV2-viremic piglets after experimental PCV2 challenge

Abstract

The objective of this study was to evaluate the effect of porcine circovirus type 2 (PCV2) vaccines on PCV2-viremic and -seropositive piglets born from naturally PCV2-infected sows against postnatal PCV2 challenge. The experimental design was aimed at mimicking commercial swine rearing conditions to evaluate the response of the PCV2 vaccine on PCV2-viremic and -seropositive piglets after experimental PCV2 challenge. PCV2a (or 2b)-viremic piglets received a PCV2 vaccine at 21 days of age followed by a PCV2b (or 2a) challenge at 49 days of age (28 days post vaccination). The PCV2 vaccines elicited a high level of humoral (as measured by immunoperoxidase monolayer assay and neutralizing antibody titers) and cellular (as measured by the frequency of PCV2-specific interferon-γ-secreting cells) immune response in the PCV2-viremic piglets after vaccination even in the presence of maternally derived antibodies (MDA). The initial infection of PCV2 in the pigs was not affected by PCV2 vaccination, however the challenging PCV2 was reduced by PCV2 vaccination on PCV2-viremic pigs. The results from this study demonstrate that the PCV2 vaccine used in this study is effective at reducing PCV2 viremia and lymphoid PCV2 DNA, even for PCV2-viremic pigs with passively acquired MDA at the time of vaccination.

Figure 1

Quantification of PCV2b DNA in sera. Mean values of the genomic copy number of PCV2b DNA in serum from four different groups (commercial inactivated chimeric PCV1-2 vaccinated PCV2b-challenged PCV2a-viremic pigs (group 1), experimental inactivated PCV2 vaccinated PCV2b-challenged PCV2a-viremic pigs (group 2), unvaccinated PCV2b-challenged PCV2a-viremic pigs (group 5), and unvaccinated PCV2b-challenged non-PCV2-viremic pigs (group 14)) at different days post challenge. Different letters (a, b, and c) indicate statistically significant differences (P < 0.05) among groups.

Figure 2

Quantification of PCV2a DNA in sera. Mean values of the genomic copy number of PCV2a DNA in serum from four different groups (commercial inactivated chimeric PCV1-2 vaccinated PCV2a-challenged PCV2b-viremic pigs (group 7), experimental inactivated PCV2 vaccinated PCV2a-challenged PCV2b-viremic pigs (group 8), unvaccinated PCV2a-challenged PCV2b-viremic pigs (group 11), and unvaccinated PCV2a-challenged non-PCV2-viremic pigs (group 13)) at different days post challenge. Different letters (a, b, and c) indicate statistically significant differences (P < 0.05) among groups.

Figure 3

PCV2b-specific humoral and cell-mediated immune responses. Log₂ transformed group means for PCV2b-specific immunoperoxidase monolayer assay (IPMA) titers (A), neutralizing antibody (NA) titers (B), and frequency of PCV2b-specific interferon-γ-secreting cells (IFN-γ-SC)/10⁶ peripheral blood mononuclear cells (PBMC) (C) from 7 different groups (commercial inactivated chimeric PCV1-2 vaccinated PCV2b-challenged PCV2a-viremic pigs (group 1), experimental inactivated PCV2 vaccinated PCV2b-challenged PCV2a-viremic pigs (group 2), commercial inactivated chimeric PCV1-2 vaccinated unchallenged PCV2a-viremic pigs (group 3), experimental inactivated PCV2 vaccinated unchallenged PCV2a-viremic pigs (group 4), unvaccinated PCV2b-challenged PCV2a-viremic pigs (group 5), unvaccinated unchallenged PCV2a-viremic pigs (group 6), and unvaccinated PCV2b-challenged non-PCV2-viremic pigs (group 14)). Different letters (a, b, c, and d) indicate statistically significant differences (P < 0.05) among groups.

Figure 4

PCV2a-specific humoral and cell-mediated immune responses. Log₂ transformed group means for PCV2a-specific immunoperoxidase monolayer assay (IPMA) titers (A), neutralizing antibody (NA) titers (B), and frequency of PCV2a-specific interferon-γ-secreting cells (IFN- γ-SC)/10⁶ peripheral blood mononuclear cells (PBMC) (C) from 7 different groups (commercial inactivated chimeric PCV1-2 vaccinated PCV2a-challenged PCV2b-viremic pigs (group 7), experimental inactivated PCV2 vaccinated PCV2a-challenged PCV2b-viremic pigs (group 8), commercial inactivated chimeric PCV1-2 vaccinated unchallenged PCV2b-viremic pigs (group 9), experimental inactivated PCV2 vaccinated unchallenged PCV2b-viremic pigs (group 10), unvaccinated PCV2a-challenged PCV2b-viremic pigs (group 11), unvaccinated unchallenged PCV2b-viremic pigs (group 12), and unvaccinated PCV2a-challenged non-PCV2-viremic pigs (group 13)). Different letters (a, b, c, and d) indicate statistically significant differences (P < 0.05) among groups.