A NEW BORRELIA SPECIES ISOLATED FROM PATIENTS WITH RELAPSING FEVER INSPAIN

Background Lyme disease and tick-borne relapsing fever are worldwide s ystemic borrelioses caused by several Borrelia species transmitted by hard ticks (family Ixodidae) and soft ticks (family Argasidae), respec tively. A previous seroepidemiological study of Lyme borreliosis showe d several serologically reactive patients with clinically atypical pre sentations, and this discovery led to the hypothesis that some of the cases of Lyme borreliosis had been caused by another borrelia organism . Methods Blood from patients in southern Spain who had suspected Lyme disease or relapsing-fever borreliosis was cultured before treatment began, isolates of Borrelia spp were inoculated into several strains o f mice of different ages. The 16S rRNA and flagellin genes of Borrelia spp were sequenced by PCR and assessed by phylogenetic analyses. Find ings We isolated a species of Borrelia from three patients with relaps ing fever and from Ornithodorus spp ticks in southern Spain. This orga nism (refractory to in-vitro cultivation) caused a relapsing spirochae taemia with multiple organ involvement in laboratory mice that recreat ed the human disease. Phylogenetic analysis showed that this organism is a previously unrecognised species. Interpretation We have discovere d a new borrelia pathogen that is closely related to the other tick-bo rne agents of relapsing fever in Europe and Africa, and which causes a relapsing systemic disease with serological similarities to Lyme borr eliosis.