Recent developments in livestock and wildlife brucellosis vaccination.

Live attenuated brucellosis vaccines have been available for protecting domestic livestock against Brucella melitensis and B. abortus for more than 60 years. Current vaccines are effective in preventing abortion and transmission of brucellosis, but poor at preventing infection or seroconversion. In addition, they can induce abortions in pregnant animals and are infectious to humans. It can be argued that current vaccines were developed empirically in that the immunological mechanism(s) of action were not determined. Current knowledge suggests that both the innate and adaptive immune responses contribute to immunity against intracellular pathogens and that binding of pathogen structures onto pattern recognition receptors (PRRs) is crucial to the development of adaptive immunity. The phagosome appears to be vital for the presentation of antigens to T-cell subtypes that provide protective immunity to intracellular pathogens. The observation that killed bacteria or subunit vaccines do not appear to fully stimulate PRRs, or mimic Brucella trafficking through phagosomes, may explain their inability to induce immunity that equals the protection provided by live attenuated vaccines. Brucella appears to have multiple mechanisms that subvert innate and adaptive immunity and prevent or minimise immunological responses. New technologies, such as DNA vaccines and nanoparticles, may be capable of delivering Brucella antigens in a waythat induces protective immunity in domestic livestock or wildlife reservoirs of brucellosis. Because of the re-emergence of brucellosis worldwide, with an increasing incidence of human infection, there is a great need for improved brucellosis vaccines. The greatest need is for new or improved vaccines against B. melitensis and B. suis.