Immunogenicity and Efficacy of a Rough Brucella suisVaccine Delivered Orally or Parenterally to Feral Swine

Abstract

Brucella suis strain 353-1 is a stable vaccine strain that is clinically safe, does not cause positive serologic responses on conventional brucellosis surveillance tests, and induces humoral and cellular immunity in swine after vaccination. In this study, we evaluated tissue clearance and immunologic responses after oral or parenteral vaccination of feral swine with 1.9 x 10 10 colony-forming units (CFU) of strain 353-1, and compared efficacy of vaccination and control treatments in protecting against infection after experimental conjunctival challenge with a virulent B. suis strain. Feral swine vaccinated orally or parentally with strain 353-1 had greater (P < 0.05) mean ELISA titers to Brucella at all sampling times after vaccination when compared to non-vaccinated swine. PBMC from swine parentally vaccinated with 353-1 at 12 or 17 weeks, or oral vaccinates at 12 weeks after vaccination, demonstrated greater (P < 0.05) antigen-specific proliferative responses when compared to responses of PBMC from non-vaccinates. At necropsy, 4 weeks after experimental challenge with virulent B. suis, non-vaccinated feral swine had greater standard tube agglutination titers and disseminated infection with higher (P < 0.05) colonization (CFU/gm) in most tissues as compared to oral or parenteral vaccinates. The virulent challenge strain was not recovered from any tissues collected from parenteral vaccinates at 4 weeks after experimental challenge. Although the challenge strain was recovered at low levels from some samples, tissue colonization in most tissues of oral vaccinates did not differ (P > 0.05) from parenteral vaccinates, but was reduced (P < 0.05) when compared to colonization in non-vaccinated swine.