Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 14, 2006
Publication Date: July 14, 2006
Citation: Stoffregen, W.C., Olsen, S.C., Bricker, B.J. 2006. Results of Vaccine Trials using Brucella Abortus RB51 in Domestic Swine. In: Proceedings of the International pig Veterinary Society, July 14-20, Copenhagen, Denmark. p. 89. Technical Abstract: With the near complete eradication of swine brucellosis from domestic pigs in the US, there is a reemergence of interest in new strategies, including candidate vaccines, to control swine brucellosis particularly in light of the wide distribution of Brucella-infected feral swine across the US. One such candidate vaccine, Brucella abortus strain RB51 (SRB51), has been previously suggested as a tool to control swine brucellosis in feral and domestic swine based on reports of its experimental usage in swine (1,2). SRB51 is a laboratory derived lipopolysaccharide O-side chain-deficient mutant of B. abortus strain 2308 (3). SRB51 induces protective immunologic responses in cattle and bison against challenge-exposure with virulent B. abortus strains. SRB51 also does not induce antibody responses that react with conventional brucellosis serologic surveillance tests (4). The studies reported herein were designed to determine the potential of parenteral administration of SRB51 to elicit an immune response as well as protection from challenge with virulent B. suis in domestic swine. Materials and Methods In Experiment 1, 51 6 w. old, crossbred domestic swine were parenterally vaccinated with 2 X10**10 cfu SRB51. Animals were bled and sacrifice at time points between 1 w. and 23 w. postvaccination (pv.). Appropriate samples were analyzed to determine humoral and cell mediated immune responses to SRB51, bacteremia, and clearance of the vaccine. Data was compared to data from 17 age matched control animals which were sham inoculated with PBS. In Experiment 2, 18 4 m. old, crossbred, domestic gilts were vaccinated parenterally with 2 X 10**10 cfu SRB51. Eight age-matched sham vaccinated animals served as controls. Humoral and cell-mediated immune responses were determined between w. 0 and 24 pv. At 10 m. of age animals were artificially inseminated. The 14 vaccinates and 8 controls which were successfully bred were challenged with 5.0 X10**7 cfu B. suis strain 3B to determine the efficacy of the vaccine. Appropriate antemortem samples were taken from all gilts post challenge to determine infection with the challenge strain. Shortly after parturition, all gilts and neonates/fetuses were euthanized and necropsied. Appropriate samples were taken for bacterial culture, serology, and histopathology. Results In both experiments 1 and 2, there were no statistically significant differences in serum antibody titers to SRB51 after vaccination. Likewise, there was no indication of the stimulation of significant cell-mediated immune responses based on data from peripheral blood mononuclear cell (PBMC) blastogenesis assays using gamma-irradiated SRB51 antigen to stimulate PBMCs. SRB51 was quickly cleared from vaccinated animals in experiment 1. SRB51 was only isolated from lymphoid tissues of 3 vaccinated animals at weeks 2 and 4 p.v. Culture data from gilts and neonates/fetuses is given in Table 1. Seroconversion rates of gilts, seropositivity rates of neonates/fetuses, and histologic lesions present in both gilts and neonates fetuses did not differ significantly between vaccinates and controls. <p>Culture+ Culture- Neonates/Fetuses Vaccinates 96(56.1%) 75 Controls 55(61.1%) 35 Litters Vaccinates 12(85.7%) 2 Controls 7(87.5%) 1 Gilts antemortem Vaccinates 8(57.1%) 6 Controls 7(87.5%) 1 Gilts necropsy Vaccinates 12(85.7%) 2 Controls 8(100%) 0 Table 1. Recovery of Brucella suis from individual neonates and farrowed litters at necropsy and gilts postinfection and at necropsy. Gilts were challenged with 5.0 X 10**7 CFU of B. suis strain 3B at day 75 of gestation. Discussion The results of this study indicate that single dose parenteral vaccination with SRB51 is not sufficiently immunogenic to induce protection from virulent challenge in domestic swine. The results of this study are contrary to those reported in the previous 2 studies dealing with SRB51 in domestic swine (1,2). Major differences between the current study and the previous studies include the use of nonvaccinated controls in the current study for statistical comparison of immune parameters, a defined challenge dosage in the current study, and the Brucella culture status of all animals (gilts and fetuses) was determined in the current study.