BackgroundHere we provide a comparative analysis of the genetic structure of populations (based onnad1mtDNA) ofIsthmiophora melisisolated from the American mink (Neogale vison), an introduced invasive species, commonly occurring in the territory of Poland, and from the striped field mouse (Apodemus agrarius).MethodsA total of 133 specimens ofI. meliswere obtained from naturally infectedN. visoncollected from six localities in Poland (108 samples) and 25 individuals ofI. melisfromA. agrarius. All sequences of thenad1gene obtained during the present study were assembled and aligned. The standard statistics for haplotype composition, i.e., the number of haplotypes, haplotype diversity, nucleotide diversity, and average number of nucleotide differences, were calculated. Haplotype analysis and visualization of haplotype frequency among populations were performed using a median-joining network.ResultsBased on the samples collected from different localities in Poland, our study revealed that the overall genetic diversity ofI. melisisolated from the American mink and of the striped field mouse do not differ significantly. The median-joining network showed that the three main haplotypes are in the centre of a star-like structure, with the remaining haplotypes as the satellites, reflecting the recent expansion of the populations.ConclusionsThe overall genetic diversity ofI. melisisolated from the American mink and striped field mouse reveals a high level of homogeneity. Moreover, regional differences in the food composition of the definitive hosts play an important role in shaping the genetic structure of the trematode populations.Graphical Abstract