EVALUATION OF WHOLE-CELL AND SUBCELLULAR VACCINES AGAINST BRUCELLA-OVIS IN RAMS

Five antigen preparations from Brucella ovis strain REO 198 were incor porated with the pluronic polymer L-121 and muramyl dipeptide and test ed as vaccines against B. ovis infection of rams. The antigenic prepar ations were: (1) a fraction enriched in outer membrane proteins and ro ugh lipopolysaccharide (hot saline extract, HS); (2) the proteins from HS substantially free of lipopolysaccharide; (3) outer membrane blebs ; (4) outer membrane-peptidoglycan complexes extracted with detergent; (5) killed whole cells. The experimental vaccines were compared with two standard vaccines, rough Brucella abortus 45/20 whole killed cells in an oil based adjuvant, and live Brucella melitensis Rev 1. Immuniz ations with non-living vaccines were performed on two occasions, 18 we eks apart. The rams were challenged with a virulent strain of B. ovis 31 weeks after the second vaccination and slaughtered 15 weeks thereaf ter. Rates of infection in groups vaccinated with Rev 1 (33%), and HS (40%) were significantly lower (P<0.005 and P<0.025, respectively) tha n that in the non-vaccinated control group (87%). Strain 45/20 was the only other vaccine that conferred a significant level of protection ( 50%) (P<0.05). The organ distribution of the infection and the level o f colonization of infected organs did not differ significantly between infected animals in the various vaccine groups and those in the unvac cinated control group. No statistically significant relationship was d etected between the magnitude of the antibody responses to the HS extr act, to outer membrane proteins, or to the rough lipopolysaccharide, a nd freedom from infection. The results indicate that the HS extract of B. ovis may represent a useful alternative to B. melitensis Rev 1 or B. abortus 45/20 as a vaccine against B. ovis.