Evaluation of the immunogenicity and safety of Brucella melitensis B115 vaccination in pregnant sheep

In spite of its limitations, Rev.1 is currently recognized as the most suitable vaccine against Brucella melitensis (the causative agent of ovine and caprine brucellosis). However, its use is limited to young animals when test-and-slaughter programs are in place because of the occurrence of false positive-reactions due to Rev.1 vaccination. The B. melitensis B115 rough strain has demonstrated its efficacy against B. melitensis virulent strains in the mouse model, but there is a lack of information regarding its potential use in small ruminants for brucellosis control. Here, the safety and immune response elicited by B115 strain inoculation were evaluated in pregnant ewes vaccinated at their midpregnancy. Vaccinated (n= 8) and non-vaccinated (n= 3) sheep were periodically sampled and analyzed for the 108 days following inoculations using tests designed for the detection of the response elicited by the B115 strain and routine serological tests for brucellosis [Rose Bengal Test (RBT), Complement Fixation Test (CFT) and blocking ELISA (ELISAb)]. Five out of the 8 vaccinated animals aborted, indicating a significant abortifacient effect of B115 inoculation at midpregnancy. In addition, a smooth strain was recovered from one vaccinated animal, suggesting the occurrence of an in vivo reversion phenomenon. Only one animal was positive in both RBT and CFT simultaneously (91 days after vaccination) confirming the lack of induction of cross-reacting antibody responses interfering with routine brucellosis diagnostic tests in most B115-vaccinated animals.