Protective Efficacy of a Chimeric KD26_E2LOM Vaccine Against Classical Swine Fever Virus Infection of Pigs.

A chimeric KD26_E2LOM strain can induce antibodies that can be partially distinguished from antibodies from classical swine fever virus (CSFV) infection. The chimeric vaccine strain was created using bovine viral diarrhea virus as the backbone; however, the entire BVDV E2 gene region was replaced with the E2 gene, which encodes the major target for neutralizing antibodies against CSFV. Pigs were vaccinated once or twice with the chimeric KD26_E2LOM strain, and protective efficacy was evaluated after subsequent challenge with virulent CSFV. Pigs inoculated with the chimeric KD26_E2LOM strain did not have a high temperature or leukopenia, and CSFV neutralizing antibodies (>64-fold) were observed from 28 days postvaccination (dpv). In addition, the level of anti-CSFV E2 antibody positivity was >0.8 (s/ value) from 30 dpv, and there were no antibody-positive individuals among the sentinel pigs. In control pigs, CSF antigen was detected in blood, nasal, and fecal samples at 5, 7, 10, 14, and 21 days postchallenge (dpc) and in several organs; however, no CSFV was detected in the organs of pigs vaccinated with the chimeric KD26_E2LOM strain, and no virus shedding or CSF antigen was detected on any dpc. Thus, the chimeric KD26_E2LOM strain protects pigs against horizontal transmission of virulent CSFV; however, this strain may have only partial potential for the differential detection of CSFV E antibodies.