Immunogenicity and efficacy of a rough Brucella suis vaccine delivered orally or parenterally to feral swine

Authors: Olsen, Steven; Wilson-Welder, Jennifer; NOL, P - Animal And Plant Health Inspection Service (APHIS); RHYAN, J - Animal And Plant Health Inspection Service (APHIS); SRIRANGATHAN, N - Virginia-Maryland Regional College Of Veterinary Medicine (VMRCVM)

Submitted to: International Journal of Vaccine Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2017
Publication Date: 2/9/2017
Citation: Olsen, S.C., Wilson-Welder, J.H., Nol, P., Rhyan, J., Srirangathan, N. 2017. Immunogenicity and efficacy of a rough Brucella suis vaccine delivered orally or parenterally to feral swine. International Journal of Vaccine Research. 2(1): 6.

Interpretive Summary: Brucella suis is an intracellular pathogen that causes reproductive losses in swine and which also causes zoonotic infections in people. Regulatory programs in domestic livestock, which include vaccination of livestock, are the most cost-efficient way to control Brucella suis and prevent human infection. The persistence of brucellosis in feral swine may pose a threat for reintroduction of brucellosis to swine or cattle in the United States. In this paper, we evaluated the immunity induced by a new rough B. suis vaccine, strain 353-1 in feral swine and domestic pigs. This vaccine strain induced strong protective immunity after oral or parenteral delivery without inducing antibody responses that cause false positive results on surveillance tests. Feral swine were more susceptible to infection with virulent Brucella suis than domestic swine. This data will be of interest to regulatory personnel, people with responsibilities for management of brucellosis in wildlife or domestic livestock, livestock owners, and other parties with interests regarding brucellosis management.

Technical 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 or domestic swine with 1.9 x 10**10 colony-forming units (CFU) of strain 353-1, and compared efficacy of vaccination treatments to non-vaccinate swine regarding protection against infection after experimental conjunctival challenge with a virulent B. suis strain. Domestic and feral swine vaccinated orally or parentally with strain 353-1 had greater (P<0.05) mean ELISA titers to Brucella at most times after vaccination when compared to non-vaccinated swine. PBMC from domestic or feral swine parentally vaccinated with 353-1 demonstrated greater (P<0.05) antigen-specific proliferative responses at 12 and 17 weeks after vaccination when compared to responses of PBMC from non-vaccinates. Proliferative responses of PBMC from oral vaccinates to Brucella antigens did not differ at any sampling time after vaccination from mean stimulation indices of PBMC from parenteral vaccinates. At necropsy, 4 or 5 weeks after experimental challenge with a virulent field strain of B. suis, non-vaccinated feral swine had more dissiminated infection with higher (P<0.05) colonization (CFU/gm) in many tissues as compared to non-vaccinated domestic swine. In both types of swine, parental vaccination reduced (P<0.05) mean colonization in most evaluated tissues when compared to colonization in tissues obtained at necropsy from non-vaccinated swine. Protection induced by parental vaccination was most pronounced in feral swine where it effectively induced sterile immunity against experimental challenge in vaccinates. Oral vaccination of feral or domestic swine also reduced (P<0.05) colonization in some tissues but protection tended to be reduced as compared to reduction of colonization in parenteral vaccinates.