An Overview of the Pathogenesis the Leishmaniasis: Investigation of Possible Viscerotropism Associated Genes of Viscerotropic<em> Leishmania tropica</em> Strains

Leishmania infantum is widely recognized as the primary causative agent of visceral leishmaniasis (VL) in Turkey, while Leishmania tropica predominantly causes cutaneous leishmaniasis (CL). Although L. tropica is capable of causing VL, such cases remain exceedingly rare. This study aimed to identify genetic factors underlying the visceralization potential of L. tropica by comparing isolates from VL and CL patients. Fourteen patients diagnosed with L. tropica infection, confirmed by parasite detection and genotyping between 2012 and 2022, were included: seven patients with VL and seven with CL. Clinical specimens were cultured for parasite isolation, and genotyping was performed via real-time PCR targeting the internal transcribed spacer 1 (ITS1) region. Differential gene expression was analyzed using quantitative real-time PCR (qRT-PCR), focusing on genes previously implicated in visceralization, including Cytochrome C Oxidase subunit IV, Metallo-peptidase (Clan MA(E), Family M32), Oligopeptidase B, Peroxidoxin 1, Peroxidoxin 2, Pyruvate kinase, and Succinyl-CoA:3-ketoacid-coenzyme A transferase. Next-generation sequencing (NGS) was conducted to detect potential mutations in these genes expressions was assessed by qRT-PCR. Results revealed significantly elevated mRNA expression levels of Peroxidoxin 1 and 2 and Cytochrome C Oxidase subunit IV in VL isolates compared to CL isolates and reference strains, showing increases of approximately 17-fold and 21-fold, respectively. These findings suggest that enhanced expression of these genes contributes to parasite survival and proliferation in visceral organs. NGS analyses identified multiple mutations within key genes such as Oligopeptidase B and Metallo-peptidase (Clan MA(E), Family M32), potentially explaining distinct pathogenic traits between VL and CL isolates. Collectively, this study identifies critical genetic factors involved in the pathogenesis of viscerotropic L. tropica infections. These findings offer significant insights into disease mechanisms, highlight potential therapeutic targets, and challenge the traditional perception of L. tropica as solely a causative agent of CL. The implications extend to developing improved diagnostic approaches, targeted therapies, and preventive strategies, thus providing a robust framework for future research.