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Louse-borne relapsing fever is caused by the bacterium Borrelia recurrentis and is among the most dangerous infectious diseases affecting humans. Outbreaks are currently being reported in countries around the Horn of Africa. Researchers from Universitätsmedizin Frankfurt and Justus Liebig University Giessen have now identified five proteins in Borrelia recurrentis, each capable of blocking components of the innate immune system and thereby enabling the bacterium to survive in the bloodstream. Elucidating the structure and function of these proteins has already contributed to the development of diagnostic tests and may provide a basis for future vaccines.
FRANKFURT. Louse-borne relapsing fever is caused by the spirochete bacterium Borrelia recurrentis, which is transmitted by body lice (not head lice). The disease was first described by Hippocrates (460–370 BC). Initial symptoms include a high fever lasting several days, followed by a fever-free interval. Typically, several recurrent episodes of fever follow. The disease can be treated with antibiotics. If left untreated, however, infection with Borrelia recurrentis is fatal in up to 20 percent of cases – particularly in regions where comprehensive medical care is not available.
Louse-borne relapsing fever is classified as a poverty-related neglected disease. During the last century, major epidemic outbreaks still occurred in Europe. Today, sporadic outbreaks are reported in countries around the Horn of Africa, including Eritrea, Ethiopia, Somalia, and South Sudan. According to individual studies, body lice infected with Borrelia are not currently found in Europe. Nevertheless, the disease attracted considerable attention in 2015, when increasing numbers of cases were diagnosed among refugees in several European countries.
Chi proteins ensure the pathogen’s survival
A research team led by Professor Peter Kraiczy, head of the Borrelia research group at the Institute of Medical Microbiology and Infection Control at Universitätsmedizin Frankfurt and Goethe University, together with scientists from Justus Liebig University Giessen, has now identified and characterized five closely related proteins that are crucial for the survival of Borrelia recurrentis in the human body. These so-called Chi proteins appear to have evolved from a common ancestor and are therefore considered homologous. By specifically binding to proteins in the blood, they prevent activation of a key component of the innate immune system: the human complement system. As a result, the Chi proteins stop the complement system from marking and destroying invading bacteria.
In addition, the Chi proteins can bind the enzyme precursor plasminogen present in the blood and convert it into active plasmin. Kraiczy explains: “We know from other pathogens that they use the body’s own plasmin to invade tissues. Together with the ability of the Chi proteins to block the complement system, this gives Borrelia recurrentis significant advantages in surviving and spreading after entering the human body.”
Development of diagnostic tests
Based on these findings, Kraiczy and his colleagues have already developed diagnostic tests, and these proteins may also serve as potential targets for vaccine development. Kraiczy explains: “Fever of unknown origin occurs in many infectious diseases, so pathogen-specific tests make it possible to quickly initiate the appropriate antibiotic treatment against the causative agent. We have already made considerable progress in this area and are currently conducting studies in Kenya and Nigeria using serological tests developed in our laboratory.”
According to the microbiologist, vaccines could play an important role in preparing for larger epidemics. “Although European body lice do not currently carry the pathogen, we must assume that future unrest and crises may once again lead to infected individuals arriving in Europe and introducing infected body lice, which could then trigger disease outbreaks here,” Kraiczy explains.
The research was funded by the State of Hesse through the LOEWE Center DRUID (Novel Drug Targets against Poverty-related and Neglected Tropical Infectious Diseases) from 2018 to 2024. The center’s goal was to advance research at Hessian universities in the fight against neglected tropical diseases. https://www.loewe-druid.de/
Professor Peter Kraiczy
Institute of Medical Microbiology and Infection Control
Universitätsmedizin Frankfurt and
Goethe University Frankfurt
Tel: +49 (0)69 6301–7165
Kraiczy@em.uni-frankfurt.de
Homepage: https://www.unimedizin-ffm.de/einrichtungen/institute/zentrum-der-hygiene/medizi... (in German)
Florian Röttgerding, Flavia Reyer, Eva Gerlach, Martin Amborn, Nadine Duschek, Tilman G. Schultze, Volker Fingerle, Chris M. Roome, Michaela Stumpf, Katja Becker, Stefan Rahlfs, Jude M. Przyborski, Peter Kraiczy, Karin Fritz-Wolf: Complement inhibition by a unique cluster of immunomodulatory outer surface proteins of Borrelia recurrentis. Nature Communications (2026) https://doi.org/10.1038/s41467-026-72359-y
Borrelia recurrentis, the causative agent of louse-borne relapsing fever, fluorescing blue in cultur ...
Quelle: Flavia Reyer
Copyright: Institute of Medical Microbiology and Infection Control, Universitätsmedizin Frankfurt
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Borrelia recurrentis, the causative agent of louse-borne relapsing fever, fluorescing blue in cultur ...
Quelle: Flavia Reyer
Copyright: Institute of Medical Microbiology and Infection Control, Universitätsmedizin Frankfurt
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