Isolation and molecular characterization of tick-borne relapsing fever Borrelia infecting Ornithodoros (Pavlovskyella) verrucosus ticks collected in Ukraine.

Tick-borne relapsing fever (TBRF) is a neglected zoonotic bacterial disease known to occur on five continents. We report a laboratory acquired case of TBRF caused by Borrelia caucasica, which is endemic in Ukraine and transmitted by Ornithodoros verrucosus ticks. We isolated spirochetes and characterized them by partially sequencing the 16s rRNA (rrs), flagellin (flaB), and DNA gyrase (gyrB) genes, and conducting a phylogenetic analysis. These analyses revealed a close relationship of Ukrainian spirochetes with the Asian TBRF species, Borrelia persica. The taxonomic and nomenclature problems related to insufficient knowledge on the spirochetes and their vectors in the region are discussed. While these findings enhance our understanding of species identities for TBRF Borrelia in Eurasia, further work is required to address the neglected status of TBRF in this part of the world. Public health practitioners should consider TBRF and include the disease into differential diagnosis of febrile illnesses with unknown etiology.