Avian schistosome Trichobilharzia szidati is a member of the largest genus within the family Schistosomatidae (Trematoda). Population genetic structure of Trichobilharzia spp. schistosomes, causative agents of cercarial dermatitis in humans, has not been studied yet. The knowledge of the genetic structure of trichobilharzian populations is essential for understanding the host-parasite coevolutionary dynamics and epidemiology strategies. Here we examined genetic diversity in three geographically isolated local populations of T. szidati cercariae inhabiting Russia based on nuclear (randomly amplified polymorphic DNA, RAPD) and mt (cox1) markers. We analyzed T. szidati cercariae shed from seven naturally infected snails of Lymnaea stagnalis. Using three random primers, we demonstrated genetic variation among populations, thus posing genetic structure across geographic sites. Moreover, T. szidati cercariae have been genetically structured among hosts (infrapopulations). Molecular variance analysis was performed to test the significance of genetic differentiation within and between local populations. Of total parasitic diversity, 18.8% was partitioned between populations, whereas the higher contribution (48.9%) corresponds to the differences among individual cercariae within infrapopulations. In contrast to RAPD markers, a 1,125-bp fragment of cox1 mt gene failed to provide any significant within-species structure. The lack of geographic structuring was detected using unique haplotypes which were determined in the current work for Moscow and Western Siberian local populations as well as obtained previously for European isolates (Czech Republic and Germany). All T. szidati/Trichobilharzia ocellata haplotypes were found to be mixed across their geographical origin.

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