A Rabbit model for evaluating the efficacy of recombinant adenovirus vaccine expressing E0-E2 antigens of classical swine fever virus

Abstract

This study investigated the efficacy of a recombinant adenovirus vaccine expressing E0-E2 antigens (rAd-E0-E2) of the classical swine fever virus (CSFV) and determined its minimum effective dose in rabbits. Forty rabbits were randomly divided into five groups. Three groups were immunized intramuscularly with rAd-E0-E2 at doses of 107.0, 106.0 and 105.0 IFU, respectively. CSFV C strain was administered to one group and saline to another group (negative control). Fourteen days after immunization, the animals were challenged intramuscularly with CSFV C strain. Stereotypical thermal responses were monitored to assess the protective efficacy of the vaccine. No typical thermal response was observed in either the 107.0 IFU or CSFV C strain groups. Mean spleen weight to body weight ratios in these groups were 0.055% and 0.05%, respectively, no evidence of hyperemia was observed in the splenic tissue, and no CSFV C strain was detected in the spleens by either RT-PCR or indirect fluorescent antibody (IFA) test. In the 106.0 IFU group, 6/8 rabbits showed typical thermal response and the spleen weight to body weight ratio was 0.074%. Further, in 6/8 rabbits, the splenic tissues showed hyperemia and virus was detected by IFA. In both 105.0 IFU and control groups, all animals developed fever and the spleen weight to body weight ratios were 0.099% and 0.102%, respectively. Severe hyperemia was observed and the virus was detected in the splenic tissue by RT-PCR and IFA. In conclusion, rAd-E0-E2 confers protection against CSFV C strain infection, and a rabbit model for evaluating the efficacy of the vaccine has been successfully established. The minimum effective dose in rabbits in this study was 107.0 IFU.