THE BRUCELLA-ABORTUS RB51 VACCINE DOES NOT CONFER PROTECTION AGAINST BRUCELLA-OVIS IN RAMS

The protective efficacy against Brucella ovis of the live vaccine Bruc ella abortus strain RB51 has been evaluated in rams using the attenuat ed B. melitensis strain Rev 1 as a reference vaccine. Sixteen Brucella -free rams, 6 months of age, were vaccinated subcutaneously with 4.18 x 10(10) c.f.u. RB51. Sixteen rams of the same condition and age were vaccinated subcutaneously the same day with 1.1 x 10(9) c.f.u. Rev 1. Fifteen similar rams were kept unvaccinated as controls. Six months af ter vaccination all rants were challenged with 3 x 10(9) c.f.u. B. ovi s and slaughtered 8 weeks thereafter for bacteriological and pathologi cal studies. The percentage of rams that were found infected was 68% ( Rev 1), 100% (RB51) and 100% (controls). At necropsy, the percentage o f organs found to be infected was significantly lower (p<0.0005) in Re v 1-vaccinated (34%) than in RB51-vaccinated rams (74%) or controls (6 9%). In conclusion, the RB51 vaccine did not confer protective immunit y against B. ovis in rams.