Regional genetic diversity and COI haplotype characterization of human-derived Enterobius vermicularis ısolates

Background: Enterobius vermicularis (pinworm) is a globally distributed intestinal nematode that primarily infects children. Despite its high prevalence, information on the molecular diversity of human-derived E. vermicularis populations remains limited, particularly in geographically diverse regions such as Türkiye. This study aimed to characterize genotype and haplotype diversity based on the mitochondrial cytochrome c oxidase subunit 1 (COI) gene in E. vermicularis egg isolates collected from humans in different regions of Türkiye. Methods: A total of 71 microscopy-positive samples were analyzed by nested PCR, and 40 COI amplicons (397 bp) yielded high-quality sequences for further evaluation. Sequence analysis revealed 16 distinct haplotypes defined by 20 polymorphic sites. Overall haplotype diversity was high (Hd = 0.871), whereas nucleotide diversity was low (π = 0.00714). Results: Among the regional populations, the highest haplotype diversity was observed in Kars (Hd = 0.895), while the highest nucleotide diversity was detected in Balıkesir/Edremit (π = 0.00927). Maximum-likelihood phylogenetic analysis demonstrated that all Türkiye haplotypes belonged to Genotype B and formed three subclusters together with previously reported human-derived reference sequences from Europe and the Middle East. Seven haplotypes showed no 100% match in GenBank and were therefore considered novel, whereas the remaining haplotypes were identical to genotype B sequences previously reported from Greece, Bulgaria, Iran, Iraq, and Türkiye. Conclusions: To our knowledge, this study presents the first COI-based haplotype dataset of E. vermicularis egg isolates from multiple regions of Türkiye and demonstrates substantial intraspecific genetic diversity despite the predominance of a single mitochondrial genotype. These findings expand current knowledge of the genetic structure of human-derived E. vermicularis in Türkiye and provide a basis for future large-scale molecular epidemiological studies. Further studies including larger sample sizes and additional genetic markers are needed.