Flavia Reyer (Frankfurt a. M. / DE), Martyna Olesiuk (Frankfurt a. M. / DE), Florian Röttgerding (Frankfurt a. M. / DE), Volker Fingerle (Oberschleißheim / DE), Abdulrahman Adamu (Sokoto / NG), Dan Waithru (Nairobi / KE), John Njeru (Nairobi / KE), Peter Kraiczy (Frankfurt a. M. / DE)
Introduction
Relapsing fever (RF) is a vector-borne zoonotic disease transmitted to humans by infected ticks or lice. Distinguished from all other Borrelia species known as causative agents of tick-borne RF, Borrelia recurrentis is only transmitted by the human body lice. Louse-borne RF (LBRF) is currently supposed to be endemic to the Horn of Africa, but it is conceivable, that refugees introduce the vectors into neighboring countries like northern Kenya. Unfortunately, there is no reliable in vitro diagnostics for RF available on the market.
Goals
The main goals of the study are (i) the improvement of our recently introduced immunoassay for LBRF by incorporating additional immunoreactive antigens and (ii) screening of serum samples collected in northern Kenya for IgG and IgM anti-Borrelia antibodies.
Materials & Methods
Highly immunoreactive antigens identified by mass spectrometry were used for two immunoassays, ELISA and Lineblot. Both immunoassays were incubated with confirmed Borrelia-positive and negative serum samples as well as, uncharacterized serum samples collected from patients with febrile symptoms in northern Kenya.
Results
Recently, GlpQ and the N-terminal fragment of ChiC (CihC-N) from Borrelia recurrentis were identified as reliable discriminatory antigens in combination with additional immunoreactive belonging to the Variable Major Proteins (VMP) of B. recurrentis to increase the sensitivity and specificity. By incorporating VMPs, in particular VlpD1, an increase in sensitivity was observed for the Line immunoblot.
Among 2,005 serum samples tested for anti-Borrelia IgG antibodies, 14.3 % were positive by ELISA. In addition, 152 randomly selected sera were screened for anti-Borrelia IgM antibodies. Unexpectedly, a high percentage of these sera tested (57.2 %) were also considered IgM positive.
Summary
The incorporation of VlpD1 leads to an increase in sensitivity of two recently introduced immunoassays. Our data on the seroprevalence of RF strongly suggest the distribution of the vector or the pathogen in the northern territories of Kenya bordered to countries where outbreaks are frequently reported.