Genetic differentiation of Southeast Asian Paragonimus Braun, 1899 (Digenea: Paragonimidae) and genetic variation in the Paragonimus heterotremus complex examined by nuclear DNA sequences.

Southeast Asian lung flukes, the causative agents of human and animal paragonimiasis, comprise at least 14 species. Of these, seven species; Paragonimus bangkokensis, P. harinasutai, P. macrorchis, P. siamensis, P. westermani, P. heterotremus and P. pseudoheterotremus were studied. Two regions of domain 1 of taurocyamine kinase; TkD1 (exon) and TkD1Int2 (intron 2), were used as genetic markers for elucidating their genetic differentiation, genetic variation, and heterozygosity. The TkD1 region was conserved between these species but can potentially be used to differentiate all seven species. However, the TkD1Int2 region had a high level of polymorphism, which is suitable for investigation of genetic variation within or between closely related species, especially P. heterotremus and P. pseudoheterotremus as well as for a phylogenetic analyses of the genus Paragonimus. Heterozygosity was mostly observed in DNA samples extracted from adult P. heterotremus including samples taken from sputum of paragonimiasis patients, whereas DNA extracted from metacercariae was not, except in the samples from Myanmar. Our findings provide evidence of DNA recombination and incomplete lineage sorting of P. heterotremus and P. pseudoheterotremus in TkD1Int2, which suggesting gene flow between these two species.