Genetic diversity of nuclear ITS1-5.8S-ITS2 rDNA sequence in Clonorchis sinensis Cobbold, 1875 (Trematoda: Opisthorchidae) from the Russian Far East

► Genetic diversity of C. sinensis in Russia and Korea is much lower than in China. ► ITS1 sequences differ between geographical groups, individuals, and within genome. ► ITS1 includes regulatory GC-boxes; its secondary structure depends on sequence length. ► ITS2 is conservative in both nucleotide sequence and secondary structure. ► The molecular structure of rDNA may influence parasite evolution and adaptation.