Evaluation Of A DNA Vaccine Of Classical Swine Fever By Immunopathology And Molecular Pathology

Classic swine fever (CSF) is a highly contagious viral disease caused by Classic swine fever virus (CSFV) and is a listed A disease of Office International des Epizooties (OIE). Vaccination is still the most economic strategy to control CSF. Traditional vaccines such as C-strain fall short of serological differentiation between infected and vaccinated animals. Thus, marker vaccines such as DNA vaccines are needed urgently for desirable and rational control of CSF.In a previous study, a Semliki Forest virus (SFV) replicon vectored DNA vaccine (pSFVlCS-E2) expressing the E2 glycoprotein of CSFV were shown to be able to protect pigs from lethal challenge. Lower dose and fewer vaccinations were designed to identify its efficacy. Clinical symptoms and necropsy changes were recorded. Paraffin sections were prepared and stained for morphological examination. The distribution and viral loads of CSFV were detected by immunohistochemistry (IHC). in situ hybridization histochemistry (ISHH) and in situ reverse transcription-polymerase chain reaction (ISRT-PCR) analysis in a simplified tissue microarray. Sensitivity of these three methods was compared. A nested RT-PCR served as a conformatory test was developed to detect viral RNA in paraffin-embedded tissues.At necropsy, no or less severe pathologic findings were observed in pigs immunized with pSFV1CS-E2. Microscopic observation showed that germinal centres and lymphocytic cuffs of immune organs containing increased numbers of plasma cells and lymphocytes were well developed. Control pigs immunized with pSFV1CS showed severe clinical signs of CSF.Animals immunized with pSFV1CS-E2 could suppress the viral replication due to the enhanced immune response, which could protect pigs against severe pathological changes and lethal challenge. Although the three methods developed in this study differed in sensitivity more or less, all of them could be used to evaluate the immunogenicity of the CSF vaccine and study the pathogenic mechanism of CSFV. A sensitive and repeatable method of nested RT-PCR was also established to detect the viral RNA of CSFV from paraffin-embedded tissues with results consistent with those by the others.In this study, molecular pathological technologies were used to investigate the efficacy of pSFVlCS-E2 vaccine. All the methods developed in this study are useful for evaluation of vaccines against CSF and other viral diseases, especially for retrospective study.