Diversity of Strongyloides stercoralis Isolates from Humans in Iran

Strongyloides stercoralis (S. stercoralis), the etiological agent of strongyloidiasis, is a medically important intestinal nematode that can cause life-threatening disseminated infections, particularly in immunocompromised individuals. Despite its clinical significance, limited information is available on the genetic diversity, population structure, and phylogenetic relationships of this parasite, especially in endemic regions. Therefore, generating molecular data from different geographic areas is essential for better understanding transmission patterns and epidemiology. In the present study, the intraspecies genetic diversity of S. stercoralis isolates obtained from humans in endemic regions of Iran was investigated by using mitochondrial and nuclear genetic markers. Fecal samples were collected from infected individuals in four provinces of Iran and examined using standard parasitological methods. Molecular analysis was performed through polymerase chain reaction amplification of the mitochondrial cytochrome c oxidase subunit 1 (Cox1) gene and the nuclear 18S recombinant DNA [rDNA] hypervariable regions (HVR I and IV). The obtained sequences were analyzed and aligned using Chromas (Technelysium Pty Ltd, Brisbane, Australia), BioEdit (Tom Hall, North California State University, NC), and CLC Genomics Workbench 11 (QIAGEN Sciences Inc., Germantown, MD), compared with reference sequences from GenBank, and phylogenetic trees were constructed using MEGA version 7.0 (MEGA Software GmbH, Dortmund, Germany). Haplotype networks were visualized with PopART version 1.7 (University of Otago, Dunedin, New Zealand). Analysis of 40 human isolates revealed 13 Cox1 haplotypes, of which 11 were newly identified in the present study. Notably, one haplotype clustered closely with dog-derived isolates from Japan and Cambodia. Isolates from Hormozgan Province formed distinct clades compared with other regions. Furthermore, 18S rDNA analysis revealed shared HVR-I and HVR-IV haplotypes between human and canine isolates, suggesting zoonotic transmission. Overall, the findings reveal considerable genetic diversity and regional differentiation of S. stercoralis in Iran, highlighting the need for broader multigene studies to clarify transmission dynamics and support effective control strategies.