Evaluation Of The Efficacy Of RAdV-SFV-E2Administered At Different Weeks Prior To Challenge Or Co-administered With Live HP-PRRSV Vaccine

【Objective】rAdV-SFV-E2, the adenovirus/alphavirus replicon chimeric vector-based vaccineexpressing the E2gene of classical swine fever virus (CSFV) is a potential live marker vaccinecandidate against classical swine fever. In order to make clear if the chimeric vaccine can be putinto practical use, we evaluated it regarding the first onset of full protection against lethal CSFVchallenge and the protective efficacy of co-administration with a live PRRSV HuN4-F112vaccine in this study.【Method】Groups of pigs were immunized intramuscularly (i.m.) one time with107TCID50rAdV-SFV-E2and challenged with the highly virulent CSFV Shimen strain at different weekspost-immunization (WPI). Anti-CSFV antibodies, clinical signs, viremia and pathologicalchanges were recorded and examined. Another groups of pigs were immunized i.m. withrAdV-SFV-E2alone or together with PRRSV HuN4-F112. After challenge with the highlyvirulent CSFV Shimen strain or PRRSV HuN4strain, antibodies, clinical signs, viremia andpathological changes were recorded and examined.【Results】The results of the first experiment groups showed the rAdV-SFV-E2immunized pigsdeveloped a positive level of anti-CSFV antibodies and were completely protected from thelethal challenge when challenged at3or4WPI, without fever, viremia, or pathological andhistopathological lesions. In contrast, rAdV-SFV-E2induced partly pigs developed a positivelevel of anti-CSFV antibodies and provided partial (3/5survived) or incomplete (5/5survived,but showed short-term fever and viremia) protection for the immunized pigs when challenged at1or2WPI, respectively. The other experiment groups showed that pigs co-administered withrAdV-SFV-E2and HuN4-F112developed a positive level of anti-CSFV antibodies andanti-PRRSV antibodies, without fever, viremia, or pathological and histopathological lesionswhen challenged with CSFV or PRRSV. The pigs were completely protected from the lethalchallenge with either CSFV or PRRSV and had a same protection effect with pigs whichimmunized rAdV-SFV-E2or HuN4-F112singly.【Conclusion】 The adenovirus/alphavirus replicon chimeric vector-based vaccinerAdV-SFV-E2can provide full protection against the lethal CSFV challenge at3WPI, andpartial protection at2WPI, and the protective efficacy of co-administration with PRRSVHuN4-F112and rAdV-SFV-E2is equal to that of immunization alone. It indicates thatrAdV-SFV-E2can be a promising novel marker vaccine.