P5-02 Exploring new candidates to develop a B. ovis vaccine based on S-LPS devoid mutant H38ΔwbkF and core defective derivates

Abstract

Brucella ovis, though non-zoonotic, is a serious cause of reproductive failure in sheep. No country has been declared free from this infection and eradication by test-and-slaughter has been claimed very seldom. Rev.1, the only available vaccine for small ruminants, is effective against B. melitensis (zoonotic) and B. ovis. However, Rev.1 is banned in those regions where B. melitensis is eradicated to avoid interferences in B. melitensis serosurveillance. Consequently, B. ovis is re-emerging in B. melitensis-free countries and a B. ovis specific vaccine not interfering in the smooth lipopolysaccharide (LPS) based tests used to diagnose B. melitensis is needed. In a recent work1, we demonstrated that subcutaneous vaccination of rams with the rough (R) O-polysaccharide (O-PS) mutant H38ΔwbkF confers protection similar to Rev.1 against B. ovis, while not interfering in the Rose Bengal and Complement Fixation tests used for B. melitensis diagnosis. However, since H38ΔwbkF interferes in B. ovis serodiagnosis, we also tested a B. ovis mutant (Bov::CAΔwadB) defective in the LPS-core lateral branch. While Bov::CAΔwadB did not provide protection, it caused low if any interference in the B. ovis agar gel immunodiffusion (AGID) test recommended by WOAH, an observation related to its modified core epitopes. The aim of this work was to explore whether similar LPS-core defects in H38ΔwbkF reduces the interference in B. ovis diagnosis while maintaining its efficacy against B. ovis. We constructed two mutants (H38ΔwbkFΔwadB and H38ΔwbkFΔwadC) carrying the expected core and O-PS defects, as shown by SDS-PAGE and Western-blot. In mice, both mutants showed marked attenuation with respect to H38ΔwbkF and did not protect against B. ovis. Thus, both were discarded for further research in sheep. These results confirmed the important role of the core for Brucella virulence and that over attenuation leads to ineffective vaccines. Therefore, we are exploring the use of the conjunctival route with H38ΔwbkF as a strategy to reduce the persistence of vaccinal antibodies and assessing protective efficacy of H38ΔwbkF by this route in rams.