Most of the piglets seroconverted to PCV2 between 28 and 35 days post vaccination and, although not all the animals had seroconverted by the time of challenge, they were all protected against subsequent PCV2a challenge, suggesting that strong

PCV2 antibody responses are not entirely necessary for protection (39). IM administration of a live PCV1-2 vaccine has also been demonstrated to be effective in conventional (41) and in SPF pigs (42). Similarly, combined IM and intranasal administration of live PCV2 vaccine reduced PCV2 viremia and associated lesions after challenge in SPF pigs (40). In our study, the majority of IM vaccinated pigs (21/28) had seroconverted four weeks after vaccination, which is in agreement with previous studies (39, 40, 42). In contrast, among all the PO vaccinated pigs, only 1/28 pigs had seroconverted by four weeks post vaccination. The limited ability of the experimental live-attenuated PCV1-2 vaccine to induce a measurable systemic antibody BIBW2992 cell line response may be due to limited absorption and replication. Nevertheless, as evident from the PO-non-challenged

group, PCV2 antibodies continued to increase beyond 4 weeks, indicating a delayed antibody response with the PO route of vaccination. Development of mucosal immunity by assessing presence of locally secreted PCV2 specific antibodies (for example in fecal supernatants) was not investigated, but may have given further insights into the effectiveness of this route. In this study, PCV2 DNA in sera was detectable in all treatment groups challenged with PCV2b. This is in contrast GS 1101 to previous studies where

PCV2 DNA was not detectable in vaccinated animals after challenge (39, 42). These conflicting results may Arachidonate 15-lipoxygenase be due to differences between studies in the detection methods for PCV2 DNA. For instance, the real-time PCR assay used in the current study is more sensitive than the gel-based PCR assay used previously (39). Other differences between studies include the utilization of a heterologous PCV2b challenge strain in the current study in contrast to a homologous PCV2a challenge strain used in a previous study (39). Significant differences in prevalence and amount of PCV2 DNA, with a reduction of the amount of PCV2 DNA in sera ranging from 79.2% to 84.6%, were found in pigs vaccinated IM compared to non-vaccinated pigs. Moreover, only 21.4% of pigs vaccinated by the IM route were PCV2 viremic after PCV2 challenge. Among the IM vaccinated pigs that had no detectable seroconversion prior to challenge, subsequent PCV2 viremia was not observed in 1/3 IM-PCV2-I pigs and in 3/3 IM-PCV2-PRRSV-CoI pigs, indicating evidence of protection and strengthening the importance of cellular immune response. The amount of PCV2 DNA in sera was also reduced in pigs vaccinated PO; however vaccine efficacy in the PO vaccinated groups as measured by decreased incidence and degree of viremia was not as impressive as that of the IM vaccinated groups.