The Adverse Effect of Porcine Circovirus Type 2 in the Efficacy of Lapinized Philippines Coronel Vaccine of Classical Swine Fever Virus
Date Issued
2012
Date
2012
Author(s)
Huang, Yu-Liang
Abstract
The presence of classical swine fever virus (CSFV) in Taiwan had been recorded in the Japanese era which was more than 50 years ago. During these years, Lapinized Philippine Coronel (LPC) vaccine developed by Drs. R. Lee and TC Lin is routinely used as an important tool to prevent and control CSFV infection in swine herds in Taiwan. The worldwide endemic infection of porcine circovirus type 2 (PCV2) has been reported at the end of 1990’s and the virus is also commonly present in Taiwan since then. PCV2 is able to induce post-weaning multisystemic wasting syndrome (PMWS) in PCV2-infected pigs and the syndrome is often associated with immunosuppression. The susceptible age of PCV2 infection is between 25 and 120 days old and is overlapping with the vaccination schedule of LPC vaccine. The aims of the present study are to investigate whether PCV2 infection could affect the efficacy of LPC vaccine in the pigs. The development of reverse transcription multiplex real-time PCR (RT-MRT-PCR) to detect, quantitate and genotype CSFV was the first project to proceed in this study. The results showed that the established RT-MRT-PCR was specific to CSFV and was not cross-reacted with the other swine viruses and the assay was able to differentiate various CSFV genotypes in the field samples. The detected limit of RT-MRT-PCR was 1 viral copy/μl and the sensitivity was similar as the reverse transcription nested PCR (RT-nPCR) but was more sensitive than viral isolation and RT-PCR in the field cases. The intra- and inter-assay variations of RT-MRT-PCR were below 3%. This assay was used to investigate the viremia of wild-type CSFV in vaccinated exposed pigs. The duration of viremia was longer in pigs vaccinated with E2 subunit vaccine than in pigs with LPC vaccination. The results are similar as previous studies using other detection methods which indicating RT-MRT-PCR is a rapid, sensitive, specific and reproducible, genotyping tool for CSFV detection and quantization. This assay has been used to differentiate LPC vaccine strain and wild-type CSFV strain in the field cases of Taiwan. The second project of the present study was to evaluate whether PCV2 affected the efficacy of LPC vaccine. The LPC-vaccinated pigs pre-inoculated with PCV2 showed transient fever, viremia, and viral shedding in the saliva and feces after wild-type CSFV challenge. The number of IgM+, CD4+CD8-CD25+, CD4+CD8+CD25+, and CD4-CD8+CD25+ lymphocyte subsets and the level of neutralizing antibodies against CSFV were significantly higher in the pigs with LPC vaccination alone than in the pigs with PCV2 inoculation/LPC vaccination. Further to evaluate whether PCV2 affected the CSFV-specific cell-mediated immunity (CMI), the CSFV-specific cell proliferative response of peripheral blood mononuclear cells (PBMCs) was established in an ex vivo experiment. PCV2-derived inhibition of the CSFV-specific PBMC proliferation was demonstrated in both live and UV-inactivated PCV2. The CD25 expression of PBMCs with CSFV recall antigens was also interfered by PCV2 infection. This situation was also reflected to LPC-vaccinated pigs pre-inoculated with PCV2 had low CD25 expression of lymphocyte subpopulations. In addition, in order to investigate the possible mechanisms of the PCV2-derived interference, an in vitro model was established to study the interaction of LPC and PCV2 in porcine alveolar macrophages (AMs). The results showed that PCV2 reduced the LPC infection and replication in AMs and the levels of PCV2-derived interference were dose-dependent. Both C9 CpG-ODN and full-length PCV2 DNA were able to reduce the LPC infection in AMs but the UV-inactivated PCV2 and soluble factors including TNF-α, IFN-γ, IL-8, and TGF-β1 were not involved in this interference. The experimental results of PCV2-derived interference on LPC infection were contradictory to the PCV2-derived interference on the CSFV-specific PBMC proliferation. The UV-inactivated PCV2 but not CpG-ODN of PCV2 genome is able to reduce CSFV-specific PBMC proliferation. The conclusions of the present study indicate that PCV2 infection decreases the efficacy of LPC vaccine by blocking the LPC infection and replication; as well as down-regulating both of CSFV-specific humoral and CMI response. This PCV2-derived interference may not only allow the invasion of wild-type CSFV in pig farms but also increase the difficulty of CSF prevention and control in the CSF endemic areas.
Subjects
classical swine fever virus
Lapinized Philippine Coronel
porcine circovirus type 2
real-time PCR
peripheral blood mononuclear cells
proliferative response
alveolar macrophages
SDGs
Type
thesis
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