Introduction: Digenean trematodes are among the most important parasites with complex life cycles, in which the cercarial stage plays a decisive role in disease transmission. Freshwater snails, particularly Bithynia tentaculata, are recognized as the first intermediate hosts of many trematodes, and their wide distribution in western and central Iran highlights the need for investigating associated parasitic infections. Given the difficulty of species-level identification of cercariae based solely on morphological characteristics, this study aimed to investigate trematode infection in B. tentaculata and to identify the isolated species using molecular methods in the Khorramabad region.
Materials and Methods: Snails were collected from natural habitats, and trematode cercariae were isolated from them. After DNA extraction, the parasite 28S rRNA gene was amplified by PCR, and the resulting products were sequenced.
Results: BLAST analysis revealed that the examined cercariae showed the highest genetic similarity to Pleurogenoides medians (family Pleurogenidae). Phylogenetic analysis further confirmed this finding, as the study samples clustered within the species-specific clade of P. medians.
Conclusion: The identification of P. medians in B. tentaculata represents the first molecular report of this species in Iran and the first record of its occurrence in a first intermediate host in the country. Previous reports of this trematode have mainly been from definitive hosts, particularly amphibians. These findings not only expand the known geographical range and host spectrum of P. medians but also emphasize the importance of assessing larval trematodes in freshwater snails and their potential role in the transmission cycles of pathogenic parasites in Lorestan Province. The results of this study provide a basis for future research on parasite epidemiology, ecology, and the assessment of environmental risks associated with larval trematodes in Iranian freshwater ecosystems.