Tick-borne relapsing fever (TBRF) is caused by spirochete bacteria of the genus Borrelia termed relapsing fever Borreliae (RFB). TBRF shares symptoms with Lyme disease (LD) caused by related Lyme disease Borreliae (LDB). TBRF and LD are transmitted by ticks and occur in overlapping localities worldwide. Serological detection of antibodies used for laboratory confirmation of LD is not established for TBRF. A line immunoblot assay using recombinant proteins from different RFB species, termed TBRF IB, was developed and its diagnostic utility investigated. The TBRF IBs were able to differentiate between antibodies to RFB and LDB and had estimated sensitivity, specificity, and positive and negative predictive values of 70.5%, 99.5%, 97.3%, and 93.4%, respectively, based on results with reference sera from patients known to be positive and negative for TBRF. The use of TBRF IBs and analogous immunoblots for LD to test sera of patients from Australia, Ukraine, and the USA with LD symptoms revealed infection with TBRF alone, LD alone, and both TBRF and LD. Diagnosis by clinical criteria alone can, therefore, underestimate the incidence of TBRF. TBRF IBs will be useful for laboratory confirmation of TBRF and understanding its epidemiology worldwide.
Keywords: Lyme disease; borreliosis; line immunoblots; relapsing fever; relapsing fever Borreliae; serological diagnosis.