Ultra-structure, genetic characterization and Immunological approach of fish borne zoonotic trematodes (Family: Heterophyidae) of a redbelly tilapia

Fish-borne zoonotic trematodes (FBZT) are highly significant zoonotic trematodes that can infect humans by eating raw or undercooked fish harboring active metacercaria. In this investigation, FBZT was found in samples of widely cultivated redbelly tilapia (Tilapia zillii) obtained from the Fayum governorate. Encysted metacercaria (EMC) infection was identified in fish belonging to the heterophyid family morphologically. The prevalence of heterophyid EMC was 30.5%. EMC was identified and implemented in a subsequent study on domestic pigeons (Columba livia domestica) carried out to allow adult flukes of Pygidiopsis (P.) genata; P. summa; and Ascocotyle (A.) pindoramensis species in their small intestine. This study presents the first report that combines ultra-structure, molecular approach of three species of heterophyid flukes, ultra-structure using transmission electron microscope in P. genata, and the study of host immunological responses and associated cytokines during Pygidiopsis species infection of pigeons in Egypt. Using Quantitative Real-time PCR (qRT- PCR), the gene expression levels of six cytokines (IL-1, IL-2, IL-6, IL-10, IFN-γ and TGF-β3) were assessed. The molecular confirmation of P. genata, P. summa, and A. pindoramensis have a registration in the GenBank under accession number MT672308.1, OR083433.1, and OR083431.1, respectively. Throughout the infection, the gut produced cytokines in considerably variable amounts. As a result of the Pygidiopsis species infection in pigeons, our data showed distinctive cytokine alterations, which could aid in figuring out the immunological pathogenesis and host defense mechanism against this infection. This study focused on different types of fish-borne trematodes, particularly the zoonotically important ones.

Scaphanocephalus spp. (Trematoda: Opisthorchiidae) in intermediate and definitive hosts of the Yucatán Peninsula, Mexico, with a re-description of Scaphanocephalus expansus

Scaphanocephalus is a small trematode genus belonging to the family Opistorchiidae. The genus currently contains only three species associated with marine fish as intermediate hosts and fish-eating birds as definitive hosts. Here, specimens of Scaphanocephalus were collected from the Osprey, Pandion haliaetus, and the White mullet, Mugil curema in the Yucatán Peninsula, Mexico. We report for the first-time DNA sequences of adult specimens of Scaphanocephalus, particularly S. expansus, as well as a sequence of a different species sampled as metacercaria. Morphological comparisons of Scaphanocephalus expansus confirmed the identity of the adult specimens, with minor morphological variations; Scanning electron photomicrographs were included, and the species was re-described. Phylogenetic analysis based on 28S rDNA sequences showed that Scaphanocephalus is monophyletic within Opisthorchiidae and consists of three independent lineages. Sequences of adults are identical to those of S. expansus. Instead, the sequence of the metacercaria sampled from the mesentery of Mugil curema nested with specimens reported as Scaphanocephalus sp. from a labrid fish in the Mediterranean Sea, herein named it as Scaphanocephalus sp. 2.

Molecular evidence of the absence of Metagonimus yokogawai (Katsurada, 1912) in Europe: report of Metagonimus sp. in cyprinoid fish from the River Danube in Hungary

Trematodes of the genus Metagonimus Katsurada, 1912 (Digenea: Heterophyidae) are zoonotic parasites that cause infections in humans, with most cases reported in Southeast Asia. Larvae from the second intermediate host, called metacercariae, of one of human-infecting species, M. yokogawai (Katsurada, 1912), have been reported from cyprinoid fish in Europe. In the present study, we provided DNA-based evidence that metacercariae of Metagonimus, which are commonly found in the scales of various cyprinoids in Central Europe (Danube River in Hungary) do not belong to M. yokogawai. Sequence analysis of the ITS region, 28S rDNA, and cox1 genes showed that this species is clearly distinct from all Asian species, including M. yokogawai, which probably does not occur in Europe. Metacercariae from cyprinoids might belong to Metagonimus romanicus (Ciurea, 1915), an insufficiently known species described from Romania.

Cytochrome b as a more promising marker for analysing the distribution vector for Metagonimus suifunensis (Trematoda: Heterophyidae)

In this study of Metagonimus suifunensis (M. suifunensis) in the Russian Southern Far East, the variability of the full-length sequences of the cytochrome b (cytb) mtDNA gene was assessed for the first time. In addition, the cox1 mtDNA gene sequences were also obtained for this species from new localities. In total, 87 and 81 sequences of the cytb and cox1 genes, respectively, were used in the current study. The cytb gene proved more promising and revealed two haplogroups that are associated with the spatial distribution of the species: geographical isolation caused the fixation of differences between northern and southern populations. In addition, the results obtained for the cytb gene opened up new perspectives in the analysis of sequences of the cox1 gene, which was not sufficiently effective as a sole marker. Based on data for both mitochondrial genes, molecular processes influencing the formation of the modern population were analysed for M. suifunensis. The new data confirmed the previously expressed opinion that this species colonized the study territory from north to south and will form the basis for determining possible ways of its further expansion, which is important for predicting the emergence of new foci of metagonimosis.

Current Knowledge of Small Flukes (Digenea: Heterophyidae) from South America

Fish-borne heterophyid trematodes are known to have a zoonotic potential, since at least 30 species are able to infect humans worldwide, with a global infection of around 7 million people. In this paper, a ‘state-of-the-art’ review of the South American heterophyid species is provided, including classical and molecular taxonomy, parasite ecology, host-parasite interaction studies and a list of species and their hosts. There is still a lack of information on human infections in South America with undetected or unreported infections probably due to the information shortage and little attention by physicians to these small intestinal flukes. Molecular tools for specific diagnoses of South American heterophyid species are still to be defined. Additional new sequences of Pygidiopsis macrostomum, Ascocotyle pindoramensis and Ascocotyle longa from Brazil are also provided.

Molecular characterization and confocal laser scanning microscopic study of Pygidiopsis macrostomum (Trematoda: Heterophyidae) parasites of guppies Poecilia vivipara

Pygidiopsis macrostomum and Ascocotyle (Phagicola) pindoramensis (Digenea: Heterophyidae) parasitize guppies as intermediate hosts and, respectively, fish-eating mammals or birds as definitive hosts. Heterophyids have zoonotic potential, and molecular studies associated with morphological and ecological aspects have helped to clarify their taxonomy and phylogeny. Poecilia vivipara naturally parasitized by metacercariae of both species (100% prevalence) exhibit no external signs of parasitism. In this work, four new sequences of P. macrostomum (18S rDNA, 28S rDNA and ITS2 rDNA) and one new sequence of A. (P.) pindoramensis (mtDNA cox-1) are presented. Phylogeny reconstructions linked P. macrostomum to other heterophyids, but the separation of the Heterophyidae and Opisthorchiidae remains unclear. Additionally, we used indirect immunocytochemistry and the phalloidin-fluorescence techniques allied with confocal laser scanning microscopy to describe muscular and neuronal structures of P. macrostomum. A complex arrangement of muscular fibres is associated with the tegument, suckers, gut and reproductive system. Radial fibres around the ventral sucker are thick, branched and extend to the body wall. High-resolution confocal imaging revealed a typical digenean muscular arrangement and important heterophyid morphological traits. These data will support future control measures to reduce the parasitism in guppies reared in fish farming systems, especially for aquarium and experimental purposes.

Epidemiological and molecular data on heterophyid trematode metacercariae found in the muscle of grey mullets (Osteichthyes: Mugilidae) from Sardinia (western Mediterranean Sea)

This study is a contribution to the molecular taxonomy and epidemiology of heterophyid (Trematoda: Heterophyidae) metacercariae found in the muscle of Mugilidae (Osteichthyes) from Sardinia (western Mediterranean Sea). Sixty specimens of mugilids (13 Chelon labrosus, 18 Liza aurata, 6 Liza ramada, 8 Liza saliens, 15 Mugil cephalus) were examined and 17,899 metacercariae isolated in 95 % of the hosts. Four types of metacercariae were identified: Heterophyes sp. (n = 14,113), Heterophyes sp. -small (1225), Stictodora sp. (1606), and Ascocotyle (Phagicola) sp. (955). The experimental infection of a hamster with Heterophyes sp. metacercariae produced six adults identified as Heterophyes heterophyes and two as Heterophyes cf. nocens. The morphology of Heterophyes sp. -small metacercariae matched with that of Heterophyes dispar. The sequence analysis of the ITS2 and 28S portions of rDNA confirmed the morphological identification of metacercariae, showing four clusters. All adults grouped together with the Heterophyes sp. metacercariae, whereas adults of Heterophyes nocens from Korea clustered separately, showing that this species is distinguished from H. heterophyes, and suggesting caution in the exclusive use of the number of rodlets of the genital sucker to separate the two species. The presence of metacercariae was high in all hosts; the highest prevalence is of Heterophyes sp. (prevalence ≥78 %; mean intensity ≥135 metacercariae/100 g muscle), and the most heavily infected host is M. cephalus (prevalence = 100 %; mean intensity = 841 metacercariae/100 g muscle).

First molecular identification of Ascocotyle (Phagicola) longa in its first intermediate host the mud snail Heleobia australis

This is the first study that used species-specific DNA primers to confirm the presence of the heterophyid Ascocotyle (Phagicola) longa Ransom, 1920 in its first intermediate host. The larval stages (rediae and cercariae) of this parasite were morphologically and genetically identified in the gonad of the intertidal mud snail Heleobia australis (d'Orbigny, 1835) (Cochliopidae) in the Bahía Blanca estuary, Argentina. In addition, we asked whether the prevalence in H. australis varied between seasons. Mullets - the second intermediate host of this heterophyid - migrate in estuaries during the warmer seasons and it is expected that piscivorous birds and mammals - the definitive hosts - prey more intensively on this species at those times. Thus, the number of parasite eggs released into the tidal flat within their feces should be higher, thereby increasing the ingestion of the parasite by H. australis.We therefore expected a higher prevalence of A. (P.) longa in H. australis in the Bahía Blanca estuary during spring and summer than autumn and winter. We found that 16 out of 2,744 specimens of H. australis had been infected with A. (P.) longa (total prevalence of 0.58%). Nonetheless, the prevalence showed no significant variation between seasons. Hence, we discuss an alternative scenario where the lack of seasonal changes might be mostly related to the permanent residence of definitive hosts in the estuary and not to the seasonal recruitment of mullets. Finally, we highlight the need for more experimental and comparative approaches in order to understand the diagnosis and geographical distribution of this worldwide heterophyid.

Developmental and Phylogenetic Characteristics of Stellantchasmus falcatus (Trematoda: Heterophyidae) from Thailand

This study aimed to investigate the infection status, worm development, and phylogenetic characteristics of the intestinal trematode, Stellantchasmus falcatus. The metacercariae of S. falcatus were detected only in the half-beak (Dermogenus pusillus) out of the 4 fish species examined. Their prevalence was 90.0%, and the intensity of infection was 919 metacercariae on average. Worms were recovered from 33 (97.1%) of 34 chicks that were experimentally infected with 200 S. falcatus metacercariae each, and the average recovery rate was 43.0%. The body size and inner organs of S. falcatus quickly increased in the experimental chicks over days 1-2 post-infection (PI). In addition, ITS2 sequence data of this parasite were analyzed to examine the phylogenetic relationships with other trematodes using the UPGMA method. The results indicated that the ITS2 sequence data recorded from trematodes in the family Heterophyidae appeared to be monophyletic. This study concluded that D. pusillus serves as a compatible second intermediate host of S. falcatus in Thailand and that S. falcatus can develop rapidly in the experimental chicks. Data collected from this study can help to close the gap in knowledge regarding the epidemiology, biology, and phylogenetic characteristics of S. falcatus in Thailand.

Co-infection with Opisthorchis viverrini and Haplorchis taichui detected by human fecal examination in Chomtong district, Chiang Mai Province, Thailand

Diseases caused by the liver fluke, Opisthorchis viverrini and the minute intestinal fluke, Haplorchis taichui, are clinically important, especially in the Northeast and North regions of Thailand. It is often difficult to distinguish between these trematode species using morphological methods due to the similarity of their eggs and larval stages both in mixed and co-infections. A sensitive, accurate, and specific detection method of these flukes is required for an effective epidemiological control program. This study aimed to determine the prevalence of O. viverrini and H. taichui infections in human feces by using formalin-ether sedimentation and high annealing temperature random amplified polymorphic DNA (HAT-RAPD) PCR methods. Fecal specimens of people living along the Mae Ping River, Chomtong district were examined seasonally for trematode eggs using a compound microscope. Positive cases were analyzed in HAT-RAPD, DNA profiles were compared with adult stages to determine the actual species infected, and specific DNA markers of each fluke were also screened. Our results showed that out of 316 specimens, 62 were positive for fluke eggs which were pre-identified as O. viverrini and H. taichui. In addition, co-infection among these two fluke species was observed from only two specimens. The prevalence of H. taichui infections peaked in the hot-dry (19.62%), gradually decreased in the rainy (18.18%), and cool-dry seasons (14.54%), respectively. O. viverrini was found only in the hot-dry season (6.54%). For molecular studies, 5 arbitrary primers (Operon Technologies, USA) were individually performed in HAT-RAPD-PCR for the generation of polymorphic DNA profiles. The DNA profiles in all 62 positives cases were the same as those of the adult stage which confirmed our identifications. This study demonstrates the mixed infection of O. viverrini and H. taichui and confirms the extended distribution of O. viverrini in Northern Thailand.

Development of HAT-RAPD marker for detection of Stellantchasmus falcatus infection

The trematode, Stellantchasmus falcatus, is one of the members in the Family Heterophyidae, which is reported to be an endemic fluke in northern region of Thailand. A sensitive and specific detection of this parasite is required to determine the epidemiology at larval stages. Specific primers to determine the presence of S. falcatus were investigated using high annealing temperature random amplified polymorphic DNA (HAT-RAPD) PCR, with 10 arbitrary primers to generate different polymorphic DNA profiles. Eleven parasite species were used for comparison. A 380 bp HAT-RAPD S. falcatus-specific marker was found, and was cloned and sequenced, allowing a pair of primers (St-F 5'-GGCCAACG CAATCGTCATCC-3' and St-R 5'-GCGTCGGGTTTCAGACATGG- 3') to be designed to produce a 320 bp amplicon specific for S. falcatus. It revealed no cross-reaction with any of the other tested parasite species. The S. falcatus-specific primers can be used for epidemiological monitoring and for detection in snail intermediate hosts, which serve as usefulness tools in management and epidemiological control programs.

Copro-DNA diagnosis of Opisthorchis viverrini and Haplorchis taichui infection in an endemic area of Lao PDR

The utility of differential copro-DNA diagnosis using modified sample preparation steps of small liver and minute intestinal fluke infections was tested. Fecal samples containing parasite eggs were washed extensively with diluted detergent solution. Parasite eggs were concentrated by sedimentation and broken by microwaving before DNA extraction. PCR targeting ITS1 and ITS2 regions were performed using primer specific for Opisthorchis viverrini, Haplorchis taichui and other related species. Of 125 fecal samples, 94 were positive for small trematode eggs by a modified cellophane thick smear method. By ITS1-PCR, 52 samples were positive for O. viverrini, 12 H. taichui and 7 mixed infection. By ITS2-PCR, 63 were positive for O. viverini, 17 H. taichui, and 19 mixed infection. The ITS-PCR assay identified a higher number of opisthorchiasis cases than those with O. viverrini expelled after treatment, but for H. taichui, ITS-PCR identified less than half of the worm expelled cases. These results showed that copro-DNA diagnosis was useful for the differential diagnosis of O. viverrini and H. taichui infection, which could not be discriminated by microscopy.

Development of PCR-based diagnosis of minute intestinal fluke, Haplorchis taichui

Haplorchis taichui specific primers were designed using a high annealing temperature random amplified polymorphic DNA (HAT-RAPD) PCR method and 18 arbitrary primers (Operon Technologies) to generate polymorphic DNA profiles for 13 different parasites. The H. taichui specific fragment was screened. A 256 bp HAT-RAPD marker generated from OPP-11 primer specific for H. taichui was cloned and sequenced. From the sequence data, specific primers were designed that generated a 256 bp amplicon. The minimum DNA template needed for PCR detection was 10 fg. The successful development of the H. taichui specific DNA-based detection will be beneficial in management and epidemiological control programs.

Copro-diagnosis of Haplorchis taichui infection using sedimentation and PCR-based methods

Fifty-one human fecal specimens were collected from villagers inhabiting along Mae Kuang River, Ban Sob Tha, Pa Sang District, Lamphun Province, Thailand. By the formalin-ether sedimentation technique (FEST) under a light microscope, eggs of 3 helminth species, Haplorchis taichui, Ascaris lumbricoides and unidentified hookworm species were detected with prevalences of 22, 14 and 4%, respectively. PCR amplification with H. taichui specific primers showed that H. taichui specific amplicon 260 bp was generated in all FEST-positive specimens, and also in some FEST negative specimens. This H. taichui specific PCR method can be used to detect this parasite in all developmental stages and in both definitive and intermediate hosts, which should be useful in prevention and control programs.

A new PCR-based approach indicates the range of Clonorchis sinensis now extends to Central Thailand

Differentiation of the fish-borne trematodes belonging to the Opisthorchiidae, Heterophyidae and Lecithodendriidae is important from a clinical and epidemiological perspective, yet it is impossible to do using conventional coprological techniques, as the eggs are morphologically similar. Epidemiological investigation therefore currently relies on morphological examination of adult worms following expulsion chemotherapy. A PCR test capable of amplifying a segment of the internal transcribed spacer region of ribosomal DNA for the opisthorchiid and heterophyid flukes eggs taken directly from faeces was developed and evaluated in a rural community in central Thailand. The lowest quantity of DNA that could be amplified from individual adults of Opisthorchis viverrini, Clonorchis sinensis and Haplorchis taichui was estimated at 0.6 pg, 0.8 pg and 3 pg, respectively. The PCR was capable of detecting mixed infection with the aforementioned species of flukes under experimental conditions. A total of 11.6% of individuals in rural communities in Sanamchaikaet district, central Thailand, were positive for ‘Opisthorchis-like’ eggs in their faeces using conventional parasitological detection techniques. In comparison to microscopy, the PCR yielded a sensitivity and specificity of 71.0% and 76.7%, respectively. Analysis of the microscopy-positive PCR products revealed 64% and 23% of individuals to be infected with O. viverrini and C. sinensis, respectively. The remaining 13% (three individuals) were identified as eggs of Didymozoidae, presumably being passed mechanically in the faeces following the ingestion of infected fishes. An immediate finding of this study is the identification and first report of a C. sinensis–endemic community in central Thailand. This extends the known range of this liver fluke in Southeast Asia. The PCR developed herein provides an important tool for the specific identification of liver and intestinal fluke species for future epidemiological surveys.

It is estimated that approximately 17 million people are currently infected with fish-borne flukes worldwide. The fish-borne liver flukes Opisthrochis viverrini and Clonorchis sinensis cause hepatic and biliary disease in humans. The minute intestinal flukes are widely distributed in southeast Asia and are increasingly recognised as an emerging pathogen associated with diarrhoea and gastritis. The most significant finding of this study is the discovery and first report of a C. sinensis–endemic community in Thailand. This finding was aided by the development and application of a new PCR-based technique capable of specifically detecting and characterising O. viverrini, C. sinensis and the minute intestinal flukes, directly from eggs in faeces. Since the eggs are morphologically similar, the fish-borne flukes cannot be differentiated on basis of microscopic examination of stool. This publication also questions the presumption that the distribution of fish-borne liver fluke species in Asia closely parallels the distribution of the snail intermediate hosts. The PCR provides a useful diagnostic tool for further large-scale epidemiological surveys to be carried out in Southeast Asia, which will shed further light on the distribution of these liver flukes in human and snail intermediate hosts with the advantage that targets for more arduous anthelmintic flushing confirmations can be carried out.

Sequence comparisons of 28S ribosomal DNA and mitochondrial cytochrome c oxidase subunit I of Metagonimus yokogawai, M. takahashii and M. miyatai

We compared the DNA sequences of the genus Metagonimus: M. yokogawai, M. takahashii, and M. miyatai. We obtained 28S D1 ribosomal DNA (rDNA) and mitochondrial cytochrome c oxidase subunit I (mtCOI) fragments from the adult worms by PCR, that were cloned and sequenced. Phylogenetic relationships inferred from the nucleotide sequences of the 28S D1 rDNA and mtCOI gene. M. takahashii and M. yokogawai are placed in the same clade supported by DNA sequence and phylogenic tree analysis in 28S D1 rDNA and mtCOI gene region. The above findings tell us that M. takahashii is closer to M. yokogawai than to M. miyatai genetically. This phylogenetic data also support the nomination of M. miyatai as a separate species.

Use of rDNA polymorphism for identification of Heterophyidae infecting freshwater fishes

Infections by trematodes are among the most common fish-borne zoonoses. Metacercariae of the Family Heterophyidae in marine and freshwater fishes are nonfastidious in their choice of definitive hosts, and therefore, cause infections in human and domestic animals. In the present study, species-specific polymerase chain reaction (PCR) assays were developed for identifying and differentiating the various species examined. Sequencing and aligning the 18S (SSU) rDNA revealed interspecific variation for which species-specific DNA oligonucleotides were designed and used for the identification of 6 heterophyid species recovered from piscivorous birds. The oligonucleotides were further used to evaluate the various stages (cercariae recovered from snails, metacercariae recovered from fish and adult trematodes) of the digeneans. By applying this method we elucidated for the first time the life cycle of Pygidiopsis genata. The phylogenetic interrelationship among the newly sequenced species of Heterophyidae is outlined.

Molecular differentiation of three species of Metagonimus by simple sequence repeat anchored polymerase chain reaction (SSR-PCR) amplification

Genomic DNAs from 3 species of Metagonimus in the Republic of Korea, M. yokogawai, M. miyatai, and M. takahashii, were amplified by simple sequence repeat anchored polymerase chain reaction. Primers of 3' or 5' termini of the (CA)n repeats were used; 3 kinds of 3' anchored primers (CA)8RG, (CA)4RG, and (CA)8RY, and 2 kinds of 5' anchored primers BDB(CA)7C and DBDA(CA)7. The results showed distinguishable banding patterns among the 3 species of Metagonimus, suggesting that they have different genotypes.

A cytogenetic study on human intestinal trematodes of the genus Metagonimus (Digenea: Heterophyidae) in Korea

In order to analyze chromosome numbers and karyotypes of intestinal trematodes belonging to the genus, Metagonimus, the gonad tissues of M. takahashii, M. miyatai, and M. yokogawai were prepared and examined. The number of bivalents in the first meiotic division of M. takahashii was nine (n = 9). The diploid number of M. miyatai was observed to be eighteen (2n = 18) and their chromosomes consisted of one pair of metacentric, 7 pairs of submetacentric, and one pair of telocentric chromosomes. The diploid number of M. yokogawai was thirty-two (2n = 32) and the chromosome complements were composed of two pairs of metacentric, 11 pairs of submetacentric, and three pairs of subtelocentric chromosomes. These results could be a supporting evidence for the validity of the new species, M. miyatai, distinct from M. yokogawai.

PCR-RFLP pattern of three kinds of Metagonimus in Korea

We tried to compare the three kinds of Metagonimus species, M. yokogawai, Metagonimus Miyata type, and M. takahashii, which were known to be distributed in Korea with polymerase chain reaction based-restriction fragment length polymorphism (PCR-RFLP) patterns. We amplified the internal transcribed spacer 1 (ITS1) site of ribosomal RNA and mitochondrial cytochrome c oxidase I (mCOI) gene. The restriction patterns of ITS1 gene with Rsa I, Alu I and Msp I showed multiple fragmented bands of different sizes between three kinds of Metagonimus. In case of mCOI gene, Rsa I and Alu I enzymes produced differentially fragmented band patterns. According to the parsimony analysis of PCR-RFLP patterns, the estimated genetic divergence between M. yokogawai and Metagonimus Miyata type was 0.034880, between Metagonimus Miyata type and M. takahashii was 0.028098, between M. yokogawai and M. takahashii was 0.018179. It is suggested that Metagonimus Miyata type may be separate species and evolutionize at the older time than the other two species.

Different RAPD patterns between Metagonimus yokogawai and Metagonimus Miyata type

Genomic DNA from Metagonimus yokogawai and Metagonimus Miyata type was amplified by polymerase chain reaction based on the random amplification of polymorphic DNA (RAPD) technique. Eight random 10-mer oligonucleotide primers (OPA-02, 5-TGCCGAGCTG-3; OPA-09, 5-GGGTAACGCC-3; OPA-10, 5-GTGATCGCAG-3; OPA-11, 5-CAATCGCCGT-3; OPA-13, 5-CAGCACCCAC-3; OPA-17, 5-GACCGCTTGT-3; OPA-19, 5-CAAACGTCGG-3; OPA-20, 5-GTTGCGATCC-3) with a G + C content of 60-70% (Kit A, Operon Technologies Inc., California, USA) could produce distinguishable banding patterns between the two Metagonimus species. From the results of this study, it was suggested that Metagonimus Miyata type has a different DNA sequence from M. Yokogawai.