Swali, PBooth, TTan, CCSMcCabe, JAnastasiadou, KBarrington, CBorrini, MBricking, ABuckberry, JBüster, LCarlin, RGilardet, AGlocke, IIrish, JDKelly, MKing, MPetchey, FionaPeto, JSilva, MSpeidel, LTait, FTeoaca, AValoriani, SWilliams, MMadgwick, RMullan, GWilson, LCootes, KArmit, IGutierrez, MGvan Dorp, LSkoglund, P2025-08-132025-08-132025Swali, P., Booth, T., Tan, C. C. S., McCabe, J., Anastasiadou, K., Barrington, C., Borrini, M., Bricking, A., Buckberry, J., Büster, L., Carlin, R., Gilardet, A., Glocke, I., Irish, J. D., Kelly, M., King, M., Petchey, F., Peto, J., Silva, M., . . . Skoglund, P. (2025). Ancient Borrelia genomes document the evolutionary history of louse-borne relapsing fever. Science, 388(6749). https://doi.org/10.1126/science.adr21470036-8075https://hdl.handle.net/10289/17577Several bacterial pathogens have transitioned from tick-borne to louse-borne transmission, which often involves genome reduction and increasing virulence. However, the timing of such transitions remains unclear. We sequenced four ancient Borrelia recurrentis genomes, the agent of louse-borne relapsing fever, dating from 2300 to 600 years ago. We estimated the divergence from its closest tick-borne relative to 6000 to 4000 years ago, which suggests an emergence coinciding with human lifestyle changes such as the advent of wool-based textiles. Pan-genome analysis indicated that much of the evolution characteristic of B. recurrentis had occurred by ~2300 years ago, though further gene turnover, particularly in plasmid partitioning, persisted until ~1000 years ago. Our findings provide a direct genomic chronology of the evolution of this specialized vector-borne pathogen.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Journal Article10.1126/science.adr21471095-920331 Biological Sciences3105 Genetics3 Good Health and Well Being