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

Wood mouse (Apodemus sylvaticus L.) as intermediate host for Mesocestoides canislagopodis (Rudolphi, 1810) (Krabbe 1865) in Iceland

Mesocestoides canislagopodis is a common parasite of the arctic fox (Vulpes lagopus) in Iceland. In the past, household dogs (Canis familiaris) and cats (Felis catus) were also reported in Iceland to be infected. Recently, scolices of a non-maturing Mesocestoides sp. were detected in the intestines of the gyrfalcon (Falco rusticolus), and tetrathyridia were isolated in the body cavity of rock ptarmigan (Lagopus muta) and subsequently described. All stages were confirmed, using both morphological and molecular methods, to belong to the same species, M. canislagopodis. In the present study, post-mortem examination of wood mice (Apodemus sylvaticus), sampled in autumn 2014 on a farm in Northeast Iceland, revealed the presence of tetrathyridia in the peritoneal cavity and in the liver. Most tetrathyridia in the peritoneal cavity were free, but some were encapsulated in a thin connective tissue stroma and loosely attached to the inner organs. They appear as whitish, heart-shaped, flattened, unsegmented bodies with a slightly pointed posterior end. In the liver, tetrathyridia were seen as pale-tanned nodules embedded in the parenchyma. Comparative molecular analysis, both at the generic level (D1 domain LSU ribosomal DNA), and at the specific level (cytochrome c oxidase subunit I (cox1) and 12S mitochondrial DNA), revealed that the tetrathyridia belonged to M. canislagopodis. A. sylvaticus represents a new second intermediate host record in Iceland, and the first description of a rodent as intermediate host for this species, thus participating in the life cycle of the parasite.

Ancient DNA of Metagonimus yokogawai Recovered from Joseon Period Human Remains Newly Discovered at Goryeong County in South Korea

PURPOSE

Metagonimiasis, commonly seen in East Asian countries, is a parasitic disorder caused by definitive hosts' ingestion of undercooked freshwater fishes. Recently, genetic analysis has proved 28S rRNA and cytochrome c oxidase subunit I (COI) mtDNA gene to be a successful marker differentiating species of the genus Metagonimus. In the present study, using specimens from the newly discovered Joseon Dynasty human remains of Goryeong, we obtained updated genetic data on genus Metagonimus, which was also prevalent during the Joseon period.

METHODS

The ancient DNA (aDNA) was retrieved from the coprolite sample of the seventeenth century, half-mummified individual discovered at Goryeong Country, South Korea. Cloning and sequencing were performed on PCR-amplified amplicons for M. yokogawai 28S rRNA and COI mtDNA gene. The consensus sequences were used for species identification and phylogenetic analysis using NCBI/BLAST and MEGA X software.

RESULTS

Based on the COI mtDNA gene region, the Goryeong sequence was confirmed as belonging to M. yokogawai, as it was shown to form a separate cluster with other M. yokogawai taxa that are distinct also from M. takahashii and M. miyatai.

CONCLUSION

In a series of our genetic analyses on genus Metagonimus using samples retrieved from Joseon-period cases, aDNA sequences of genus Metagonimus revealed in South Korea thus far are those of M. yokogawai, but not of M. miyatai or M. takahashii yet.

Morphological and molecular identification of Cryptocotyle lingua metacercariae isolated from Atlantic cod (Gadus morhua) from Danish seas and whiting (Merlangius merlangus) from the English Channel

Trematode larvae (metacercariae) causing black spot disease occur frequently in gills, fins, skin and the superficial muscle layers of marine fish. Species within the genus Cryptocotyle Lühe, 1899 are frequently associated with this disease. Descriptions of the metacercarial stage are relatively limited and none has hitherto been reported from fish from the English Channel. The present study reports the morphological and molecular identifications of encysted black spot-inducing parasites from whiting (Merlangius merlangus) and Atlantic cod (Gadus morhua) caught respectively from the north coast of France (English Channel) and from Danish sea waters. Metacercariae were characterised morphologically based on microscopic observations and molecularly using Sanger sequencing of fragments of the mitochondrial cox1 gene and rDNA ITS region. Morphological data were compared with available data in the literature. Phylogenetic trees including reference sequences were built to confirm morphological and molecular identifications. This survey constitutes the first description of C. lingua metacercariae in the English Channel ecosystems.

Metagonimus yokogawai Ancient DNA Recovered from 16th- to 17th-Century Korean Mummy Feces of the Joseon Dynasty

Metagonimiasis is foodborne intestinal parasitism occurring by the definitive hosts' ingestion of raw or undercooked fish, mostly commonly sweetfish. Most Metagonimus infection is caused by Metagonimus yokogawai but also rarely by Metagonimus takahashii as well as Metagonimus miyatai. Despite recent molecular work on Metagonimus spp., there are still insufficient data to reveal the genetic characteristics of ancient M. yokogawai in a wide geo-historical scope. In this study, we were successful in the analysis of M. yokogawai ancient DNA (aDNA) using coprolite samples retrieved from 16th- to 17th-century Korean mummies. In BLAST and phylogenetic analyses, M. yokogawai 28S rDNA of Korean mummies were clustered along with the 28S rDNA taxa of M. takahashii and M. miyatai in GenBank. Conversely, the cytochrome c oxidase subunit I (COI) of M. yokogawai aDNA from Korean mummies was distinctly clustered apart from M. takahashii and M. miyatai sequences. This study is the first report of its kind to identify M. yokogawai aDNA retrieved from the archaeological specimens and confirms the usefulness of COI in molecular diagnosis of M. yokogawai. Considering the rarity of reports on the genetics of genus Metagonimus spp., our study will be fundamental for the future study of M. yokogawai paleogenetics.

Characterization of the mitochondrial genome sequences of the liver fluke Amphimerus sp. (Trematoda: Opisthorchiidae) from Ecuador and phylogenetic implications

Amphimerus Barker, 1911 is a liver fluke infecting several animal species and humans. Being a digenetic trematode of the Opisthorchiidae family, Amphimerus is closely related to the genera Metorchis, Clonorchis and Opisthorchis. Recently, a high prevalence of Amphimerus infection in humans, cats, and dogs had been demonstrated in a tropical Pacific region of Ecuador. Hence, we determined and characterized the entire mt genome sequences of adult liver flukes, morphologically identified as Amphimerus, collected in the endemic region of Ecuador, and examined its phylogenetic relationships with flukes in the Opisthorchiidae family using Bayesian inference (BI) based on the concatenated amino acid sequences and partial cox1 sequences. The complete mt genome sequence (15, 151 bp in length) of the Amphimerus sp. contains 35 genes, including 12 protein-coding genes (PCGs, without atp8), two rRNAs (rrnL and rrnS) and 21 tRNAs, lacking trnG. The gene content and arrangement of the Ecuadorian Amphimerus mt genome was similar to those of other trematodes in the Opisthorchiidae family. All genes in the circular mt genome of Amphimerus sp. are transcribed from the same strand in one direction, with the A + T content of 60.77%. Genetic distances between Amphimerus sp. and other genera in Opisthorchiidae were rather high, ranging from 26.86% to 28.75% at nucleotide level and 29.37%-31.12% at amino acid level. Phylogenetic analysis placed the Ecuadorian Amphimerus within the branch of Opisthorchiidae, but very distinct from Opisthorchis. Our results indicate that the liver fluke Amphimerus from Ecuador does not belong to the genus Opisthorchis, and that it should be assigned under the genus Amphimerus. The determination of the mt genome of the Ecuadorian Amphimerus provides a new genetic resource for future studies on taxonomy and molecular epidemiology of Opisthorchiidae trematodes.

Fishborne zoonotic heterophyid infections: An update

Fishborne heterophyid trematodes infecting humans are at least 29 species worldwide and belong to 13 genera. Its global burden is much more than 7 million infected people. They include Metagonimus (M. yokogawai, M. takahashii, M. miyatai, M. minutus, and M. katsuradai), Heterophyes (H. heterophyes, H. nocens, H. dispar, and H. aequalis), Haplorchis (H. taichui, H. pumilio, H. yokogawai, and H. vanissimus), Pygidiopsis (P. summa and P. genata), Heterophyopsis (H. continua), Stellantchasmus (S. falcatus), Centrocestus (C. formosanus, C. armatus, C. cuspidatus, and C. kurokawai), Stictodora (S. fuscata and S. lari), Procerovum (P. varium and P. calderoni), Acanthotrema (A. felis), Apophallus (A. donicus), Ascocotyle (A. longa), and Cryptocotyle (C. lingua). Human infections are scattered around the world but the major endemic areas are located in Southeast Asia. The source of human infection is ingestion of raw or improperly cooked fish. The pathogenicity, host-parasite relationships, and clinical manifestations in each species infection are poorly understood; these should be elucidated particularly in immunocompromised hosts. Problems exist in the differential diagnosis of these parasitic infections because of close morphological similarity of eggs in feces and unavailability of alternative methods such as serology. Molecular diagnostic techniques are promising but they are still at an infant stage. Praziquantel has been proved to be highly effective against most of the patients infected with heterophyid flukes. Epidemiological surveys and detection of human infections are required for better understanding of the geographical distribution and global burden of each heterophyid species. In this review, the most updated knowledge on the morphology, biology, epidemiology, pathogenesis and pathology, immunology, clinical manifestations, diagnosis and treatment, and prevention and control of fishborne zoonotic heterophyid infections is provided.

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).

Occurrence of Mesocestoides canislagopodis (Rudolphi, 1810) (Krabbe, 1865) in mammals and birds in Iceland and its molecular discrimination within the Mesocestoides species complex

The life cycle of Mesocestoides tapeworms (Cestoda: Cyclophyllidea: Mesocestoididae) requires three hosts. The first intermediate host is unknown but believed to be an arthropod. The second intermediate host is a vertebrate. The primary definitive host is a carnivore mammal, or a bird of prey, that eats the tetrathyridium-infected second intermediate host. One representative of the genus, Mesocestoides canislagopodis, has been reported from Iceland. It is common in the arctic fox (Vulpes lagopus) and has also been detected in domestic dogs (Canis familiaris) and cats (Felis domestica). Recently, scolices of a non-maturing Mesocestoides sp. have also been detected in gyrfalcon (Falco rusticolus) intestines, and tetrathyridia in the body cavity of rock ptarmigan (Lagopus muta). We examined the taxonomic relationship of Mesocestoides from arctic fox, gyrfalcon, and rock ptarmigan using molecular methods, both at the generic level (D1 domain LSU ribosomal DNA) and at the specific level (cytochrome c oxidase subunit I (COI) and 12S mitochondrial DNA). All stages belonged to Mesocestoides canislagopodis. Phylogenetic analysis of the combined 12S-COI at the specific level confirmed that M. canislagopodis forms a distinct clade, well separated from three other recognized representatives of the genus, M. litteratus, M. lineatus, and M. corti/vogae. This is the first molecular description of this species. The rock ptarmigan is a new second intermediate host record, and the gyrfalcon a new primary definitive host record. However, the adult stage seemed not to be able to mature in the gyrfalcon, and successful development is probably restricted to mammalian hosts.

Molecular characterization of Stictodora tridactyla (Trematoda: Heterophyidae) from Kuwait Bay using rDNA ITS and mtCO1

Stictodora tridactyla is an intestinal fluke in the family Heterophyidae that parasitizes shorebirds and mammals, including humans. Its metacercarial cyst stage was reported in the Arabian killifish, Aphanius dispar, at Kuwait Bay. In the present study, Cerithidea cingulata was found to serve as the first intermediate host of S. tridactyla. In order to establish the snail-fish link in the life cycle of S. tridactyla, complete sequences of ribosomal DNA internal transcribed spacer region 1 and 2 (rDNA ITS1 and ITS2) and partial sequence of cytochrome oxidase subunit 1 were obtained for metacercarial cysts isolated from the fish A. dispar and rediae isolated from the snail C. cingulata. Sequence alignment demonstrated that these larval stages belong to the same heterophyid species, S. tridactyla. Phylogenetic analysis based on rDNA ITS1, ITS2, and mtCO1 confirmed the position of S. tridactyla within the Heterophyidae and found it to cluster with Haplorchis spp. The present study represents the first molecular study correlating the larval stages of S. tridactyla using rDNA ITS1, ITS2, and mtCO1 and examining the phylogenetic relationships of S. tridactyla with different heterophyid species.

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.

Molecular phylogeny of trematodes in Family Heterophyidae based on mitochondrial cytochrome c oxidase subunit I (mCOI)

OBJECTIVE

To analyze a phylogenetic tree for understanding the molecular systematic of trematode in Family Heterophyidae, which are highly distributed in Thailand.

METHODS

Based on thirteen sequences of mitochondrial cytochrome c oxidase subunit I (mCOI) gene from six genera of heterophyid trematodes, viz. Haplorchis, Stellantchasmus, Centrocestus, Metagonimus, Pygidopsis, and Haplorchoides were aligned automatically using the Clustal × 2.0 program. A phylogenetic tree was constructed by maximum likeinghood (ML) and neighbor-joining (NJ) methods, with 1 000 bootstrap using the 5.0 program.

RESULTS

The phylogenetic relationship from both methods was similar and separated into three groups consisting of Haplorchoides pumilio group, Haplorchoides taichui group and another heterophyid genera.

CONCLUSIONS

The sequence data of mtCOI can be used to investigate the phylogenetic relationships of trematodes at the genus level. Each clade of different genera of heterophyid trematodes can be separated into sister groups that correlated with the morphological characteristic, kind of secondary intermediate host and geographic distribution.

Development of a polymerase chain reaction applicable to rapid and sensitive detection of Clonorchis sinensis eggs in human stool samples

Microscopic examination of eggs of parasitic helminths in stool samples has been the most widely used classical diagnostic method for infections, but tiny and low numbers of eggs in stool samples often hamper diagnosis of helminthic infections with classical microscopic examination. Moreover, it is also difficult to differentiate parasite eggs by the classical method, if they have similar morphological characteristics. In this study, we developed a rapid and sensitive polymerase chain reaction (PCR)-based molecular diagnostic method for detection of Clonorchis sinensis eggs in stool samples. Nine primers were designed based on the long-terminal repeat (LTR) of C. sinensis retrotransposon1 (CsRn1) gene, and seven PCR primer sets were paired. Polymerase chain reaction with each primer pair produced specific amplicons for C. sinensis, but not for other trematodes including Metagonimus yokogawai and Paragonimus westermani. Particularly, three primer sets were able to detect 10 C. sinensis eggs and were applicable to amplify specific amplicons from DNA samples purified from stool of C. sinensis-infected patients. This PCR method could be useful for diagnosis of C. sinensis infections in human stool samples with a high level of specificity and sensitivity.

Life cycle of Renylaima capensis, a brachylaimid trematode of shrews and slugs in South Africa: two-host and three-host transmission modalities suggested by epizootiology and DNA sequencing

Background

The life cycle of the brachylaimid trematode species Renylaima capensis, infecting the urinary system of the shrew Myosorex varius (Mammalia: Soricidae: Crocidosoricinae) in the Hottentots Holland Nature Reserve, South Africa, has been elucidated by a study of its larval stages, epizootiological data in local snails and mammals during a 34-year period, and its verification with mtDNA sequencing.

Methods

Parasites obtained from dissected animals were mounted in microscope slides for the parasitological study and measured according to standardized methods. The mitochondrial DNA cox1 gene was sequenced by the dideoxy chain-termination method.

Results

The slugs Ariostralis nebulosa and Ariopelta capensis (Gastropoda: Arionidae) act as specific first and second intermediate hosts, respectively. Branched sporocysts massively develop in A. nebulosa. Intrasporocystic mature cercariae show differentiated gonads, male terminal duct, ventral genital pore, and usually no tail, opposite to Brachylaimidae in which mature cercariae show a germinal primordium and small tail. Unencysted metacercariae, usually brevicaudate, infect the kidney of A. capensis and differ from mature cercariae by only a slightly greater size. The final microhabitats are the kidneys and ureters of the shrews, kidney pelvis and calyces in light infections and also kidney medulla and cortex in heavy infections. Sporocysts, cercariae, metacercariae and adults proved to belong to R. capensis by analysis of a 437-bp-long cox1 fragment, which was identical except for three mutations in metacercariae, of which only one silent. Epizootiological studies showed usual sporocyst infection in A. nebulosa and very rare metacercarial infection in A. capensis, which does not agree with high prevalences and intensities in the shrews.

Conclusions

The presence of monotesticular adult forms and larval prevalences and intensities observed suggest that R. capensis may use two transmission strategies, a two-host life cycle by predation of A. nebulosa harbouring intrasporocystic cercariae may be the normal pattern, whereas a second mollusc host is just starting to be introduced. In shrews, a tissue-traversing, intraorganic migration followed by an interorganic migration to reach and penetrate the outer surface of either of both kidneys should occur. For first slug infection, the fluke takes advantage of the phenomenon that M. varius always urinate during defaecation. Consequently, in Brachylaimidae, the second intermediate mollusc host should evolutionarily be seen as a last addition to the cycle and their present adult stage microhabitat restricted to digestive tract and related organs as a loss of the tissue-traversing capacity of the metacercaria.

Foodborne intestinal flukes in Southeast Asia

In Southeast Asia, a total of 59 species of foodborne intestinal flukes have been known to occur in humans. The largest group is the family Heterophyidae, which constitutes 22 species belonging to 9 genera (Centrocestus, Haplorchis, Heterophyes, Heterophyopsis, Metagonimus, Procerovum, Pygidiopsis, Stellantchasmus, and Stictodora). The next is the family Echinostomatidae, which includes 20 species in 8 genera (Artyfechinostomum, Acanthoparyphium, Echinochasmus, Echinoparyphium, Echinostoma, Episthmium, Euparyphium, and Hypoderaeum). The family Plagiorchiidae follows the next containing 5 species in 1 genus (Plagiorchis). The family Lecithodendriidae includes 3 species in 2 genera (Phaneropsolus and Prosthodendrium). In 9 other families, 1 species in 1 genus each is involved; Cathaemaciidae (Cathaemacia), Fasciolidae (Fasciolopsis), Gastrodiscidae (Gastrodiscoides), Gymnophallidae (Gymnophalloides), Microphallidae (Spelotrema), Neodiplostomidae (Neodiplostomum), Paramphistomatidae (Fischoederius), Psilostomidae (Psilorchis), and Strigeidae (Cotylurus). Various types of foods are sources of human infections. They include freshwater fish, brackish water fish, fresh water snails, brackish water snails (including the oyster), amphibians, terrestrial snakes, aquatic insects, and aquatic plants. The reservoir hosts include various species of mammals or birds.The host-parasite relationships have been studied in Metagonimus yokogawai, Echinostoma hortense, Fasciolopsis buski, Neodiplostomum seoulense, and Gymnophalloides seoi; however, the pathogenicity of each parasite species and host mucosal defense mechanisms are yet poorly understood. Clinical aspects of each parasite infection need more clarification. Differential diagnosis by fecal examination is difficult because of morphological similarity of eggs. Praziquantel is effective for most intestinal fluke infections. Continued efforts to understand epidemiological significance of intestinal fluke infections, with detection of further human cases, are required.

Molecular phylogeny of parasitic Platyhelminthes based on sequences of partial 28S rDNA D1 and mitochondrial cytochrome c oxidase subunit I

The phylogenic relationships existing among 14 parasitic Platyhelminthes in the Republic of Korea were investigated via the use of the partial 28S ribosomal DNA (rDNA) D1 region and the partial mitochondrial cytochrome c oxidase subunit 1 (mCOI) DNA sequences. The nucleotide sequences were analyzed by length, G + C %, nucleotide differences and gaps in order to determine the analyzed phylogenic relationships. The phylogenic patterns of the 28S rDNA D1 and mCOI regions were closely related within the same class and order as analyzed by the PAUP 4.0 program, with the exception of a few species. These findings indicate that the 28S rDNA gene sequence is more highly conserved than are the mCOI gene sequences. The 28S rDNA gene may prove useful in studies of the systematics and population genetic structures of parasitic Platyhelminthes.

Development of Centrocestus armatus in different final hosts

In this study, Centrocestus armatus metacercariae were fed orally to hamsters, albino rats, mice, and chicks. Animals were sacrificed and dissected at 1, 3, 5, 7, and 14 days post-infection to determine the development and recovery rate of worms. Results indicated that the average worm recovery rate in hamsters was 25% on the first day post-infection and recovery continued until the 14th day with a gradual decrease in the percentage. Worms were also recovered from mice and albino rats from the first until the third day post-infection, but no worms were recovered thereafter. In chicks, worms were not observed on first day but recovery was positive at 12 h post-infection. Among the four animal hosts, feces from hamsters were the only ones positive for eggs; these were initially observed from the third day and recovery continued until 14 days post-infection. In our study, hamsters are the animal model most suitable for the study of C. armatus when compared to rats, mice, and chicks.

Fish-borne parasitic zoonoses: status and issues

The fish-borne parasitic zoonoses have been limited for the most part to populations living in low- and middle-income countries, but the geographical limits and populations at risk are expanding because of growing international markets, improved transportation systems, and demographic changes such as population movements. While many in developed countries will recognize meat-borne zoonoses such as trichinellosis and cysticercosis, far fewer are acquainted with the fish-borne parasitic zoonoses which are mostly helminthic diseases caused by trematodes, cestodes and nematodes. Yet these zoonoses are responsible for large numbers of human infections around the world. The list of potential fish-borne parasitic zoonoses is quite large. However, in this review, emphasis has been placed on liver fluke diseases such as clonorchiasis, opisthorchiasis and metorchiasis, as well as on intestinal trematodiasis (the heterophyids and echinostomes), anisakiasis (due to Anisakis simplex larvae), and diphyllobothriasis. The life cycles, distributions, epidemiology, clinical aspects, and, importantly, the research needed for improved risk assessments, clinical management and prevention and control of these important parasitic diseases are reviewed.