Molekulare und immunologische Untersuchungen bei Tsutsugamushifieber in Nepal
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Philipps-Universität Marburg
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Abstract
Orientia tsutsugamushi is an obligate intracellular Gram-negative bacterium transmitted by bites from mite larvae and the causative agent of Tsutsugamushi fever, a disease also known as “Scrub Typhus”. Nepal, a country located in the center of the Asian endemic area, has been the focus of increased research on Tsutsugamushi fever in recent years. The epidemiology of this neglected emerging infectious disease in Nepal has been described primarily from fever studies. Data on Orientia-specific immune response in the healthy Nepalese population, and in particular on seroprevalence of antibodies does not currently exist. This leaves unanswered questions regarding Orienta persistence and co-infection with severe fever with thrombocytopenia syndrome (SFTS) virus, as well as sparse molecular characterization of Orientia tsutsugamushi in Nepal.
To gain a deeper understanding of the disease in Nepal, this research represents the first characterization of the Orientia-specific IgM and IgG antibody response, by indirect immunofluorescence (IFAT), and systemic cytokine profile using multiplex immunoassay, in a healthy Nepalese population as compared to acutely ill, rapid test positive Tsutsugamushi fever patients. Additionally, serum samples from both groups were analyzed for circulating Orientia DNA by polymerase chain reaction (PCR). This was followed by molecular typing and phylogenetic analysis of human pathogenic Orientia sequences from Nepal.
This approach showed that the use of rapid tests for diagnosis of acute Tsutsugamushi fever was accurate. Furthermore, despite limited ability to assess their specificity, rapid tests proved to be significantly more sensitive than IFAT, suggesting the field should consider abandoning this laborious procedure as the gold standard.
This work is also the first to identify a high seroprevalence of Orientia-specific antibodies in the healthy Nepalese population and, in this context, to characterize more precisely the endemic occurrence of the disease in Nepal. This research demonstrates that Tsustugamushi fever is highly endemic in the Nepalese community.
Furthermore, the detection of Orientia 16S DNA in asymptomatic blood donors provides additional evidence for persistence of the pathogen in the organism even after acute Tsutsugamushi fever infection, given the high prevalence of IgG antibodies. Based on these findings, Orientia 16S DNA detections alone were shown to be highly sensitive but not indicative of acute infection. As such, multi-target PCRs with the additional target of the 47kD gene in an endemic setting like Nepal could contribute to the diagnostic discrimination of acute from previous infections.
The analysis allowed for the description of a diverse Orientia strain occurrence in Nepal, finding large homologies to other Asian Orientia strains. No evidence of SFTS virus infections emerged in this work.
The systemic cytokine profile of IL-6 and IFN-γ showed partially significant differences between the Tsutsugamushi fever patients and blood donors, from which evidence for activation of lymphocytes and the innate immune system can be deduced. TNF-α and IL-10 revealed a weak inflammatory immune response with evidence of possibly only mild disease.
The findings illuminate the clinical characteristics and provide clues for making a suspected clinical diagnosis based on the presence of symptoms such as a subjective feeling of heat, diarrhea, and enlarged inguinal lymph nodes.
The present work adds to the limited body of research on Orientia tsutsugamushi in the Nepalese context, providing more detailed data on the seroprevalence of Orientia-specific antibodies and inflammatory response in the population, as well as on appropriate molecular diagnostic targets and the heterogeneity of Orientia tsutsugamushi in the country. The findings provide new clues for improved understanding of the disease and for establishing appropriate and accurate diagnostics in Nepal. They can also contribute to improved disease management, improved control of Tsutsugamushi fever infections, and the possible development of an appropriate vaccine for Nepal.
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Created: 2022Issued: 2022-09-07Updated: 2022-09-07
Faculty
Medizin
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
Tsutsugamushi feverOrientia tsutsugamushiNepalScrub Typhus
DFG-subjects
NepalOrientia tsutsugamushiTsutsugamushifieber
DDC-Numbers
610
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En-Nosse, Nora: Molekulare und immunologische Untersuchungen bei Tsutsugamushifieber in Nepal. : Philipps-Universität Marburg 2022-09-07. DOI: https://doi.org/10.17192/z2022.0314.