No abstract

Opisthorchiasis is a zoonotic parasitic infection caused by small liver fluke species, Opisthorchis viverrini,O. felineus and Clonorchis sinensis, in the family Opisthorchiidae. Vietnam has both species, of which C.sinensis is distributed in the northern and O. viverrini in the central provinces. In addition to the mitochondrialgenomes, the ribosomal DNA sequences (rDNA) of these species are highly needed to obtain for providingmolecular markers in species identification, classification, phylogeny and evolutionary studies. In this study,the near/complete nucleotide sequences of ribosomal transcription units (rTU) from O. viverrini (Vietnamesesample), O. felineus (Russian sample) and C. sinensis (Vietnamese sample) were analyzed. All rTUs for threespecies were determined, which is 7,839 bp for O. viverrini, 6,948 bp for O. felineus and 7,296 bp for C.sinensis containing structures of 18S, ITS1, 5,8S, ITS2 and 28S. The IGS region was not obtained for all threespecies. In all three species, sequence analysis revealed 2 tandem repetitive elements of 47-48 bp/each in ITS1but not in ITS2. The nucleotide sequences of 18S, ITS1, ITS2 and 28S are valuable ribosomal markers that thisstudy provides for diagnosis, identification, taxonomic classification and population genetics. In conclusion,the rTU sequences for the three species of the family Opisthorchiidae have been identified and providesmolecular markers for the use of phylogenetic analysis for species/family classification in the superfamilyOpisthorchioidea and the class Trematoda.

Echinostomiasis is a neglected disease caused by the intestinal flukes (family Echinostomatidae, suborder Echinostomata) and is common in communities in Asian countries, such as India, Indonesia, the Philippines, China, Malaysia, Singapore, Korea, Japan, Thailand, Laos, Cambodia and Vietnam. The genetic markers from the nuclear ribosomal transcription units are commonly used in genetic studies and phylogenetic analyses. A portion of the 28S rDNA sequence (domains D1–D3, of 1062–1067 bp for the final use) was obtained from the zoonotic Echinostoma malayanum (strain E/Amala-EMI3-TH), E. revolutum (strain Erevo-MSD15-TH), E. miyagawai (Emiya-RED11-TH), and Hypoderaeum conoideum (Hcono-RED42-TH) species; and used to perform an alignment for genetic distance estimation and phylogenetic analysis. The alignment was performed using 62 strains of 42 species from 19 genera of the family Echinostomatidae, including Echinoparyphium, Echinostoma, Artyfechinostomum, Patagifer, Neoacanthoparyphium, Hypoderaeum, Echinoparyphium, Drepanocephalus, Euparyphium, Chaunocephalus, Neopetasiger, Ribeiroia, Cathaemasia, Rhopalias, Isthmiophora, Petasiger, Moliniella, Pegosomum, and Schistosoma (family Schistosomatidae). The genetic distance estimation among 16 strains/10 species has shown a low intra-specific divergence level between strains within the same species, such as E. miyagawai (0–0.10%), E. revolutum (0.10–0.50%), and H. conoideum (0–0.10%), while between strains within the same genus it was higher (normally over 1.0%) and among strains/species between genera it was the highest (3.06–4.12%). The 28S rDNA sequence analysis and phylogenetic relationship well supported the Echinostoma/ Artyfechinostomum malayanum intergeneric taxonomy and the topology indicated clear, well-supported positions of member species in different genera in the family Echinostomatidae of the suborder Echinostomata. More sensu lato samples of the genera, are required for sequencing, particularly those of zoonotic species in the five genera: Artyfechinostomum, Echinostoma, Hypoderaeum, Echinoparyphium, and Isthmiophora. The resultant mitochondrial and nuclear data obtained from these species will be a good source to use to clearly assess the taxonomic and generic relationships.

Heterophyidiasis caused by minute intestinal flukes becomes of public concern in many countries worldwide. Haplorchis taichui and H. pumilio, belonging to the family Heterophyidae (Platyhelminthes: Trematoda) are two of many infecting humans and commonly found in Vietnam. Sequence study of these two small intestinal flukes is still very limited, hence we need more prospective markers for taxonomic identification and classification. This study provides complete coding sequence of the ribosomal transcription units (rTU) from H. taichui and H. pumilio (Vietnamese samples) and demonstrates the use of complete 28S rDNA sequences for phylogenetic analysis.The complete coding sequence of the rTU (from 5' 18S to 3' 28S), consisting of complete 18S, ITS-1, 5.8S, ITS2 and complete 28S rRNA genes and spacers, from H. taichui (7,268 bp) and H. pumilio (7,416 bp) from human hosts in Vietnam, were determined and annotated. The 18S and 5.8S genes of both species were of the same length (1,992 bp/18S, 160 bp/5.8S), but 28S genes differed (3,875 bp/H. taichui and 3,870 bp/H. pumilio). ITS-1 in H. taichui (797 bp) and ITS-2 in H. pumilio (280 bp) do not contain tandem repeat units (TRUs), while ITS-1 in H. pumilio (1,106 bp) contains 3 TRUs of 136 bp/each and 2 TRUs of 116 bp/each and ITS-2 in H. taichui (444 bp) contain 3 TRUs (83–85 bp/each). A phylogenetic tree inferred from the alignment of complete 28S rDNA sequences of 32 trematode strains/species, including 2 Vietnamese Haplorchis spp. and 24 species of 8 families in the suborders Xiphidiata (families Nanophyetidae, Paragonimidae, Collyriclidae), Opisthorchiata (Heterophyidae, Opisthorchiidae), and Echinostomata (Echinostomatidae, Fasciolidae).  and Schistosoma japonicum of the family Schistosomatidae is used as an outgroup. The topology of the phylogenetic tree clearly confirmed the status of the Vietnamese H. taichui and H. pumilio species. These species gathered in a group (in the family Heterophyidae) clearly identified in the position of "sister” group to those in the family Opisthorchiidae (suborder Opisthorchiata, superfamily Opisthorchioidea).

Paragonimiasis, caused by Paragonimus species belonging to the family Paragonimidae of the suborder Xiphidiata (Platyhelminthes: Trematoda), often occurs in poor, upland, ethnic minorities, in Vietnam and the world. Asian Paragonimus species are distributed from Japan, South Korea, along with North and Southeast China, North-West and Central Vietnam, the Philippines, Thailand, Bangladesh, India, and Sri Lanka. There are various genetic variants, strains, and genotypes forming different complexes and evolutionary lineages. The 18S, 28S rDNA sequences and the intergenic transcribed spacer regions (ITS-1, ITS-2) of nuclear ribosomal transcription units are commonly used as molecular markers in genetic studies and phylogenetic analyses. We obtained a portion of 28S rDNA (domains D1–D3) of Paragonimus spp. including P. heterotremus (from Vietnam), P. ohirai (Japan), P. iloktsuenensis (Japan), and P. westermani (India and Vietnam) and conducted phylogenetic analysis for molecular evolutionary studies. The results showed that the family Paragonimidae formed the biggest cluster in a phylogenetic tree, which comprises of 46 sequences of 11 species belonging to 11 subgroups, among which the P. westermani complex of strains originating from China, Korea, Japan, India, Philippines, Malaysia, and Vietnam is present. P. westermani complex is arranged in a position of "sister" (sister group) with the subgroup P. siamensis. The P. heterotremus and P. ohirai complexes, and the P. miyazakii, P. harinasutai, P. mexicanus, P. kellicotti, and P. macrorchis complexes are clustered in a common population. P. westermani of Vietnam is in close proximity to the East Asian strains, as of which has been previously reported. P. ohirai and P. iloktsuenensis are considered “sibling” species, sharing the same clade. Phylogenetic analysis using the 28S rDNA sequences directly presented species position and their molecular evolutionary relationships in the families Paragonimidae, Troglotrematidae, Nanophyetidae, and Collyriclidae. Evolutionary analysis has also clarified a number of complex delineation problems and made a clear nomenclature for Paragonimus sp. of Vietnam, in particular, which has scientific grounds merited to recognize as that it is really the P. westermani species.