Novel approaches for the serodiagnosis of louse-borne relapsing fever

Detection of Bacterial Infections and Malaria among Blood Culture-Negative Samples of Hospitalized Febrile Patients from a Tertiary Hospital in Ethiopia

Febrile illnesses contribute significantly to morbidity and mortality in sub-Saharan Africa, but the lack of diagnostic facilities and the broad spectrum of pathogens can lead to inadequate clinical management. The timely and reliable identification of the causative pathogens in febrile patients is the basis for the administration of optimal treatment. We aimed to evaluate the performance of a multiplex polymerase chain reaction (PCR) among blood culture-negative patients presenting with febrile diseases in Central Ethiopia. From April 2016 to June 2018, we collected blood samples from adults and children ≥1 year of age admitted with febrile diseases to the Asella Referral and Teaching Hospital, which is located at an altitude of 2,400 m. Total nucleic acids were extracted from frozen plasma samples using a MagNA Pure 96 instrument (Roche, Mannheim, Germany). The multiplex PCR assays were used in combination with LightCycler multiplex DNA master mix (Roche) on a LightCycler 480 instrument (Roche). We used the pathogen-specific assays targeted to Plasmodium spp., Borrelia spp., Rickettsia spp., Leptospira spp., Salmonella spp., and arboviruses. We tested plasma samples of 511 patients and found positive results for Plasmodium spp. (13, 2.5%), Borrelia spp. (12, 2.3%), and Rickettsia species (7, 1.3%); in total, pathogens were detected in 32 of the samples (6.3%). No pathogen was detected by multiplex PCR in 94% of blood culture-negative samples. Even if the pathogens identified by PCR were not necessarily causes of fever, molecular testing using a multiplex PCR can contribute to pathogen diagnosis in a proportion of febrile patients in the highland part of Ethiopia and help to improve the clinical management.

Aetiologies of bacterial tick-borne febrile illnesses in humans in Africa: diagnostic limitations and the need for improvement

Tick-borne febrile illnesses caused by pathogens like Anaplasma spp., Bartonella spp., Borrelia spp., Ehrlichia spp., Coxiella burnetii, Francisella tularensis, and Rickettsia spp., are significant health concerns in Africa. The epidemiological occurrence of these pathogens is closely linked to the habitats of their vectors, prevalent in rural and semi-urban areas where humans and livestock coexist. The overlapping clinical presentations, non-specific symptoms, and limited access to commercially available in vitro diagnostics in resource-limited settings exacerbate the complexity of accurate diagnoses. This review aimed to systematically extract and analyze existing literature on tick-borne febrile illnesses in Africa, highlighting the diagnostic challenges and presenting an up-to-date overview of the most relevant pathogens affecting human populations. A comprehensive literature search from January 1990 to June 2024 using databases like PubMed, Cochrane Library, Science Direct, EMBASE, and Google Scholar yielded 13,420 articles, of which 70 met the inclusion criteria. Anaplasma spp. were reported in Morocco, Egypt, and South Africa; Francisella spp. in Kenya and Ethiopia; Ehrlichia spp. in Cameroon; Bartonella spp. in Senegal, Namibia, South Africa, and Ethiopia; Borrelia spp. in Senegal, Gabon, Tanzania, and Ethiopia; Coxiella burnetii in 10 countries including Senegal, Mali, and South Africa; and Rickettsia spp. in 14 countries including Senegal, Algeria, and Uganda. Data were analyzed using a fixed-effect model in R version 4.0.1 and visualized on an African map using Tableau version 2022.2. This review highlights the urgent need for improved diagnostics to better manage and control tick-borne febrile illnesses in Africa.

Serological evidence of louse-borne relapsing fever in northern Kenya

BACKGROUND

Tick- and louse-borne relapsing fever are highly-neglected, vector-borne diseases caused by diverse Borrelia species. Presently, there are no data available on the endemicity of tick- and louse-borne relapsing fever spirochetes in Kenya. Here, we present data of a retrospective study on the seroprevalence of louse-borne relapsing fever (LBRF) in northern Kenya.

METHODS

A novel immunoassay, recently established for the diagnosis of LBRF was utilized to screen 2005 blood samples collected from individuals with fever without a source in Turkana County, Kenya between May 2009 and November 2010 for anti-LBRF antibodies.

RESULTS

Out of the 2005 sera analyzed, 287 samples (14.3 %) were considered anti-LBRF IgG positive. Subsequent analyses revealed that 87 out of 152 sera randomly selected from these 2005 samples were tested positive (57.2 %) for anti-LBRF IgM antibodies. Most of the IgG and IgM positive samples were from individuals living in northern regions of Turkana County.

CONCLUSION

Our serological finding provides strong evidence for the occurrence of LBRF in Kenya.

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

Introduction

Relapsing fever (RF) remains a neglected human disease that is caused by a number of diverse pathogenic Borrelia (B.) species. Characterized by high cell densities in human blood, relapsing fever spirochetes have developed plentiful strategies to avoid recognition by the host defense mechanisms. In this scenario, spirochetal lipoproteins exhibiting multifunctional binding properties in the interaction with host-derived molecules are known to play a key role in adhesion, fibrinolysis and complement activation.

Methods

Binding of CihC/FbpC orthologs to different human proteins and conversion of protein-bound plasminogen to proteolytic active plasmin were examined by ELISA. To analyze the inhibitory capacity of CihC/FbpC orthologs on complement activation, a microtiter-based approach was performed. Finally, AlphaFold predictions were utilized to identified the complement-interacting residues.

Results and discussion

Here, we elucidate the binding properties of CihC/FbpC-orthologs from distinct RF spirochetes including B. parkeri, B. hermsii, B. turicatae, and B. recurrentis to human fibronectin, plasminogen, and complement component C1r. All CihC/FbpC-orthologs displayed similar binding properties to fibronectin, plasminogen, and C1r, respectively. Functional studies revealed a dose dependent binding of plasminogen to all borrelial proteins and conversion to active plasmin. The proteolytic activity of plasmin was almost completely abrogated by tranexamic acid, indicating that lysine residues are involved in the interaction with this serine protease. In addition, a strong inactivation capacity toward the classical pathway could be demonstrated for the wild-type CihC/FbpC-orthologs as well as for the C-terminal CihC fragment of B. recurrentis. Pre-incubation of human serum with borrelial molecules except CihC/FbpC variants lacking the C-terminal region protected serum-susceptible Borrelia cells from complement-mediated lysis. Utilizing AlphaFold2 predictions and existing crystal structures, we mapped the putative key residues involved in C1r binding on the CihC/FbpC orthologs attempting to explain the relatively small differences in C1r binding affinity despite the substitutions of key residues. Collectively, our data advance the understanding of the multiple binding properties of structural and functional highly similar molecules of relapsing fever spirochetes proposed to be involved in pathogenesis and virulence.