How a louse-borne pathogen evades the immune system

by Markus Bernards, Goethe University Frankfurt am Main

edited by Lisa Lock, reviewed by Robert Egan

Lisa Lock

Scientific Editor

Meet our editorial team
Behind our editorial process

Robert Egan

Associate Editor

Meet our editorial team
Behind our editorial process Editors' notes

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:

fact-checked

peer-reviewed publication

trusted source

proofread

The GIST Add as preferred source

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 B.C.). 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% 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."

The study is published in the journal Nature Communications.

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.

Publication details

Florian Röttgerding et al, Complement inhibition by a unique cluster of immunomodulatory outer surface proteins of Borrelia recurrentis, Nature Communications (2026). DOI: 10.1038/s41467-026-72359-y

Journal information: Nature Communications

Clinical categories

Infectious diseasesLaboratory medicine Provided by Goethe University Frankfurt am Main Who's behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021. Full profile →

Robert Egan

Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →

Citation: How a louse-borne pathogen evades the immune system (2026, June 10) retrieved 11 June 2026 from https://medicalxpress.com/news/2026-06-louse-borne-pathogen-evades-immune.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.