Human Borreliosis Caused by a New World Relapsing Fever Borrelia-like Organism in the Old World.

Background. Relapsing fever is an infectious disease previously neglected in Africa, which imposes a large public health burden in the country. We aimed to investigate and report on a case of relapsing fever borreliosis in Zambia. Methods. A previously unknown Borrelia species was isolated from the blood of a febrile patient. Investigations of the presumptive vector ticks and natural hosts for the Borrelia species were conducted by culture isolation and/or DNA detection by Borrelia-specific polymerase chain reaction. Using culture isolates from the patient and bat specimens, genetic characterization was performed by multilocus sequence analysis based on the draft genome sequences. Results. The febrile patient was diagnosed with relapsing fever. The isolated Borrelia species was frequently detected in Ornithodoros faini (n = 20/50 [40%]) and bats (n = 64/237 [27%]). Multilocus sequence analysis based on a draft genome sequence revealed that the Borrelia species isolates from the patient and presumptive reservoir host (bats) formed a monophyletic lineage that clustered with relapsing fever borreliae found in the United States. Conclusions. A febrile illness caused by a Borrelia species that was treatable with erythromycin was identified in Zambia. This is the first study to report on relapsing fever Borrelia in Zambia and suggesting the likely natural reservoir hosts of the isolated Borrelia species. Interestingly, the isolated Borrelia species was more closely related to New World relapsing fever borreliae, despite being detected in the Afrotropic ecozone.