Immunogenicity and safety of a natural rough mutant of Brucella suis as a vaccine for swine.

The objective of the current study was to evaluate the safety, immunogenicity and clearance of the natural rough mutant of Brucella suis strain 353-1 (353-1) as a vaccine in domestic swine. In three studies encompassing 105 animals, pigs were inoculated with 353-1 by conjunctival (5 × 10(7) CFU) or IM (1-2 × 10(10) CFU) routes. Clearance, tissue distribution, and pathology of the vaccine strain were determined by periodic blood culture, collection of tissues at periodic necropsy times after vaccination, and histologic evaluation of tissue samples. The B. suis 353-1 strain was nonpathogenic, cleared from most vaccinates by 10-12 weeks after vaccination, and did not induce significant histologic lesions in tissues examined. The vaccine strain appears to be phenotypically stable as all isolates recovered from vaccinates retained their rough phenotype. Vaccination induced significant humoral responses, peripheral blood mononuclear cell proliferation, and interferon-gamma (IFN-γ) production after inoculation as compared to responses of control pigs. The vaccine strain did not appear to be shed from vaccinates as co-housed sentinel animals demonstrated no serologic or microbiologic evidence of lateral transmission. Our data demonstrates that B. suis 353-1 is a stable, rough mutant that does not induce adverse clinical effects or tissue localization, but does induce significant humoral and cellular immune responses after vaccination of swine.