Re-emergence of Brucella species: epidemiology and pathogenesis

SUMMARYBrucella spp. are highly adapted intracellular bacterial pathogens that remain a substantial global cause of zoonotic disease. The globally distributed species Brucella melitensis, Brucella abortus, Brucella suis, and Brucella canis account for the majority of human infections, reflecting their efficient transmission across animal hosts, and their exceptional capacity to survive and replicate within the intracellular niche. Although animal infections are often clinically silent, human brucellosis can exhibit persistent intracellular infection and relapsing fever. Growing genomic data highlight expanding species diversity, including B. canis and marine Brucella. Progress in elucidating the intracellular life cycle of Brucella, including the maturation of Brucella-containing vacuoles, immune evasion strategies, and the role of the type IV secretion system, has refined our understanding of disease pathogenesis across hosts. At the same time, expanding molecular surveillance, global minimum-spanning-tree analyses, and One Health epidemiology have clarified transmission pathways among livestock, dogs, wildlife, and humans, revealing both cross-species connectivity and geographical hotspots of emergence. Given the limitations of existing livestock vaccines and the absence of human or canine vaccines, diverse next-generation platforms are now advancing toward translational evaluation. Unlike prior reviews focused primarily on livestock brucellosis or classical species, this review integrates emerging canine and marine Brucella lineages with advances in genomics, intracellular pathogenesis, and next-generation vaccine strategies within a unified One Health framework. In this review, we synthesize global trends in Brucella species diversity, zoonotic emergence, mechanisms of intracellular pathogenesis, and the status of current and experimental vaccines, while highlighting the One Health interventions needed to disrupt transmission and advance toward comprehensive brucellosis control.