Novel approaches for the serodiagnosis of louse-borne relapsing fever

Abstract

Louse-borne relapsing fever (LBRF) caused by B. recurrentis is a poverty-related and neglected infectious disease with an endemic focus in the Horn of Africa. Re-emergence of the disease occurred in Europe during the refugee crisis in 2015 and sporadic outbreaks were frequently reported in Eastern Africa where poor settings lack affordable diagnostics. Currently, there are no validated in vitro assays available for the serodiagnosis of LBRF. The aim of this study was to develop novel and reliable immunoassays by investigating clinically suspected and culture-confirmed serum samples from LBRF patients and a broad panel of serum samples from patients with other spirochetal, bacterial, and parasitic diseases. We identified two immunoreactive antigens (complement-inhibiting protein CihC and the glycerophosphodiester phosphodiesterase GlpQ of B. recurrentis) as the most promising target candidates leading to the evaluation of two immunoassays (line immunoblot and ELISA) for IgM and IgG. To optimize the IgM immunoassay, we conducted a bioinformatic approach to localize the relevant immunogenic regions within CihC. By utilizing a N-terminal CihC fragment, the sensitivity and specificity of both immunoassays (CihC and GlpQ) were high (IgM: sensitivity 100%, specificity of 89.9%, IgG: sensitivity 100%, specificity 99.2%). In conclusion, our findings indicate the diagnostic potential of CihC and GlpQ as valuable markers for the serodiagnosis of LBRF even at early time points of infection. Here, we provide strong evidence for the utilization of these immunoassays as reliable tools in clinical practice.

Multifunctional interaction of CihC/FbpC orthologs of relapsing fever spirochetes with host-derived proteins involved in adhesion, fibrinolysis, and complement evasion

“…The generation of His-tagged CihC orthologs from B. recurrentis A17, B. hermsii FRO, B. parkeri , and B. turicatae as well as the N- and C-terminal fragment of CihC of B. recurrentis A17 and the N-terminal fragment of the CihC ortholog of B. hermsii HS1 were described previously ( 10 , 22 ). The recombinant proteins used herein consisted the following amino acid residues: CihC of B. recurrentis (aa 20-356), FbpC of B. hermsii FRO (aa 21-374), FbpC ortholog of B. parkeri (aa 25-349), FbpC ortholog of B. turicatae (aa 21-363), CihC-N of B. recurrentis A17 (aa 20-194), CihC-C of B. recurrentis (aa 195-356), and FbpC-N from B. hermsii (aa 21-203).…”

“…The generation of His-tagged CihC orthologs from B. recurrentis A17, B. hermsii FRO, B. parkeri, and B. turicatae as well as the N-and C-terminal fragment of CihC of B. recurrentis A17 and the N-terminal fragment of the CihC ortholog of B. hermsii HS1 were described previously (10,22 To produce recombinant proteins, E. coli cultures (500 ml) were grown in ampicillin-supplemented TB medium at an OD 600 of 0.5 to 0.7 and then induced with 200 µM isopropyl-b-Dthiogalactopyranoside (Carl Roth, Karlsruhe, Germany). Cultures were then incubated for 4 h at RT.…”