The current study identified risk factors associated with porcine circovirus type 2 (PCV2) infection on pig farms in the Republic of Korea using a multinomial logistic regression model to evaluate the PCV2 infection status of pigs at different growth stages. Compulsory disinfection of visitors (odds ratio [OR]: 0.019, 95% confidence interval [CI]: <0.001–0.378, p=0.0095), compulsory registration of visitors (OR: 0.002, 95% CI: <0.001–0.184, p=0.0070), regular blood testing (OR: 0.012, 95% CI: <0.001–0.157, p=0.0007), and running on-farm biosecurity learning programs for workers (OR: 0.156, 95% CI: 0.040–0.604, p=0.0072 and OR: 0.201, 95% CI: 0.055–0.737, p=0.0155, respectively) were identified as factors which could reduce the risk of PCV2 infection. However, visitation by a regular veterinarian (OR: 32.733, 95% CI: 3.768–284.327, p=0.0016) was associated with PCV2 infection.

Porcine Circovirus Type2 (PCV2), a single-stranded DNA virus associated with Postweaning multisystemic wasting syndrome(PMWS) of swine, has two major open reading frames, ORF1 and ORF2. The genomic size and molecular weight of ORF2 is respectively 699bp, 28kDa. ORF2 encodes the capsid protein (structural protein) that has type-specific epitopes and is very immunogenic and associated with the induction of neutralizing antibodies, suggesting its potential use in diagnostic assays as well as vaccine development. For efficient production of the capsid proteins, we expressed the PCV2 ORF2 gene with baculovirus in the insect cells. In this study, PCV2 ORF2 was appropriately ligated into the baculovirus transfer vector, pBacPAK9 and pB9-Acpol19-110-EK. Sf21 cells were transfected with a mixture of the purified recombinant transfer vector and bAcGOZA. We generated and purified recombinant viruses containing PCV2 ORF2, and named rAc-B9-PCV2ORF2 and rAc-B9-19-110-EK-PCV2ORF2, respectively. Expression levels of capsid fusion proteins with a partial polyhedrin region of AcNPV more increased than recombinant proteins from non-fusion expressed. Also, expression efficiency increased over time and differed at MOI. As a results, fusion expression of porcine circovirus type2 ORF2 using baculovirus could be utilized as an alternative expression method to produce recombinant antigen against PCV2 infection and is worthy of further investigation.

Porcine circovirus type 2 (PCV2) is associated with porcine circovirus diseases (PCVD), of which postweaning multisystemic wasting syndrome is considered to cause considerable economic losses in pig industry worldwide. As the virus-like particle (VLP) is a highly effective type of subunit vaccine and has unique advantages in terms of safety and immunogenicity, this study aimed to develop PCV2-like particles, which matched currently circulating Korean PCV2 and were applicable as vaccines. The ORF2 genes encoding PCV2 capsid protein were amplified from the PCV2 subgroup 1A/B Korean C275 isolate and the subgroup 2E C94 isolate by PCR assay with primer pair specific to PCV2 ORF2 gene, and were cloned into baculovirus transfer vector. Recombinant baculovirus was generated by cotransfection with the transfer vector and linear baculovirus DNA into the Sf9 cells, and then by plaque purification. Expression of PCV2 capsid protein was determined by the indirect immunofluorescence and Western blotting assays, and electron microscopy. By both immunological assays, PCV2 capsid antigen was detected in the Sf9 cells infected with the recombinant baculoviruses. The formation of empty virus particles, characteristic of VLP, was detected in the lysate of Sf9 cells infected with the recombinant baculoviruses by negative electron microscopy. From these results, VLPs of two genogroups of PCV2 were successfully expressed and generated in a baculovirus expression system. It is expected that the expressed VLPs of two genotypic groups can be used for control of PCV2 infection as good vaccine candidates.