Genomic analysis of Brucella Ovis in Italy reveals high genetic diversity and a novel lineage

BACKGROUND: Brucella ovis, the causative agent of ovine brucellosis, poses an underestimated threat to sheep farming worldwide due to its impact on reproductive health and flock productivity. Although B. ovis is non-zoonotic, the disease is globally distributed and often excluded from mandatory control programs, especially in Europe, resulting in scarce prevalence data and limited genomic information that hinder effective management strategies. This study investigated the global and regional phylogenetic structure of B. ovis using Multilocus Variable-Number Tandem Repeat (MLVA) analysis, core genome Multilocus Sequence Typing (cgMLST), and Single Nucleotide Polymorphism (SNP) analysis. Strains from the Americas, Europe, Oceania, and a novel Italian dataset were analyzed to better understand the evolutionary dynamics and distribution of this pathogen. RESULTS: MLVA revealed limited continental clustering and the presence of shared genotypes across geographically distant regions. cgMLST analysis identified two dominant sequence types: the globally distributed ST-13 and a novel, Italy-specific ST-97. While ST-13 showed significant allelic diversity, ST-97 was found exclusively in two geographically distant Italian isolates. Italian strains demonstrated higher genomic diversity overall, forming multiple distinct clusters. SNP analysis confirmed these observations, highlighting clear geographic segregation within Italy and close genetic relationships between some Italian strains and those from Spain, Croatia, and the USA. Notably, ST-97 strains lacked the virulence-associated btpA gene and exhibited a 34-gene deletion, including putative prophage-related genes. CONCLUSION: The findings reveal novel aspects of B. ovis phylogeography, emphasizing the unexpectedly high genetic diversity within Italy and identifying a distinct lineage (ST-97) with potential differences in virulence and adaptability. These insights enhance our understanding of the global epidemiology of B. ovis and may inform the development of targeted control strategies.