Sequences of Internal Transcribed Spacers and Two Mitochondrial Genes: Effective Genetic Markers for Metorchis orientalis

Digenean trematodes (Trematoda: Digenea) parasitizing the digestive system of the great cormorant (Phalacrocorax carbo) in Hungary

Great cormorants (Phalacrocorax carbo) are widespread piscivorous birds, which cause huge economic losses in the fish fauna worldwide. As a consequence of their predatory behaviour, they serve as definitive hosts for many digenean trematodes, and their digestive systems usually contain several parasite species. Between 2019 and 2022, 131 bird carcasses were collected from Biharugra (Hungary) as culling on the cormorant population. Their digestive systems were subjected to parasitological examination. The studied organs (131 intestines, 44 stomachs and 21 pharynxes) were opened, and their contents were settled in water, filtered, and sorted under microscope. For species identification, sequence analysis of the ITS region was performed. Of the 131 birds, 118 were infected by tapeworms or nematodes, 105 with trematodes, and 10 were parasite-free. The vast majority of obtained sequences (57 of the 105 trematodes) belonged to the genus Petasiger (43/57) and Hysteromorpha triloba (13/57). A single specimen of Metorchis sp. (1/57) as a zoonotic trematode was recorded during our survey. The results confirmed the high trematodes prevalence of the examined cormorants. However, most of them are not considered as human pathogens.

Morpho-Molecular Features and Phylogenetic Relationships of Metorchis butoridi Oschmarin, 1963 (Trematoda: Opisthorchiidae) from East Asia

Adult trematodes of the genus Metorchis were found in the gallbladders of ducklings that had been experimentally fed freshwater fishes of the genera Rhynchocypris and Rhodeus that were naturally infected by Metorchis metacercariae. Some of the trematodes were identified as Metorchis ussuriensis, whose morphology of developmental stages and molecular data had previously been described in detail. The other trematodes were confirmed as species Metorchis butoridi on the basis of morphological features: subterminal oral sucker, vitelline follicles with interrupted bands, and rosette-shaped testes. An analysis of phylogenetic relationships within Opisthorchiidae using nuclear and mitochondrial markers confirmed that the obtained trematodes were actually from the genus Metorchis. The morphological and molecular features indicated that a number of trematodes found in East Asia and described as Metorchis orientalis belong to M. butoridi. Also, the M. orientalis individuals from Europe are, in fact, representatives of another Metorchis species.

Prevalence of fish-borne zoonotic trematode infection in Jilin Province, China

Fish-borne zoonotic trematodes (FZTs) are the most serious food-borne parasites in Asia and have become a burden to public health and a new challenge in food safety. In Jilin Province, China, the prevalence of FZTs in intermediate and definitive hosts has not been extensively explored. In the present study, we investigated the prevalence of FZTs in Jilin Province, China. From July to November 2020, a total of 132 freshwater snails (the first intermediate host of FZTs), 4122 wild freshwater fishes (the second intermediate host of FZTs) and 143 fecal samples from canines, ducks and swine (the definitive host of FZTs) were collected from the Yitong River basin of Jilin Province. FZT species were identified by morphological observation combined with internal transcribed spacer (ITS) sequence analysis. The prevalence of FZTs was then calculated. The results showed that the prevailing species of FZTs in Jilin Province, China, were Clonorchis sinensis, Metorchis orientalis and Echinochasmus japonicus. The total prevalence of FZTs was 29.74% (1226/4122) in fish, the total infection rates were 2.27% (3/132) in snails, 75.00% (21/28) in canines and 37.18% (29/78) in ducks. The coinfection rates of the two trematodes were 13.39% (552/4122) in fish, 35.71% (10/28) in canines and 7.69% (6/78) in ducks. The coinfection rate of the three flukes was 2.60% (107/4122) in fish. Nine of the 12 fish species examined were infected with FZT metacercariae.

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sinensis, M. orientalis and E. japonicus were reported in Jilin province of China.

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The prevalence of FZTs in freshwater fish were 29.74% (1226/4122).

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Four fish species were identified as new second intermediate hosts of E. japonicus.

A review of molecular identification tools for the opisthorchioidea

The superfamily Opisthorchioidea encompasses the families Cryptogonimidae, Opisthorchiidae and Heterophyidae. These parasites depend on the aquatic environment and include marine and freshwater species. Some species, such as Clonorchis sinensis and Opisthorchis viverrini, have a high impact on public health with millions of infected people worldwide and have thus been the object of many studies and tool developments. However, for many species, tools for identification and detection are scarce. Although morphological descriptions have been used and are still important, they are often not efficient on the immature stages of these parasites. Thus, during the past few decades, molecular approaches for parasite identification have become commonplace. These approaches are efficient, quick and reliable. Nonetheless, for some parasites of the superfamily Opisthorchioidea, reference genomic data are limited. This study reviews available genetic data and molecular tools for the identification and/or the detection of this superfamily. Molecular data on this superfamily are mostly based on mitochondrial and ribosomal gene sequence analyses, especially on the cytochrome c oxidase subunit 1 gene and internal transcribed spacer regions respectively.

First case report of Metorchis orientalis from Black Swan

Metorchis orientalis belongs to the genus Metorchis of Opisthorchiidae, which mainly parasitizes in liver and bile ducts of waterfowl, causing liver dysfunction of the host. It has been reported that M. orientalis also infects humans. As a natural species in Australia and a popular ornamental animal, Black Swan (Cygnus atratus) has been imported into many countries. At present there has been no report of M. orientalis infection in Black Swan. In the present study M. orientalis infection in Black Swan was identified by a combination of different techniques, including morphological observation and molecular analysis. M. orientalis adults were found in the gallbladder and bile duct of a three-year-old female Black Swan, which was further confirmed by internal transcribed spacer (ITS) sequence analysis. In addition, the intermediate and definitive hosts of M. orientalis from the ‘Qing’ lake (a man-made lake in Changchun, China) that Black Swan lived were investigated and the infection route was preliminarily determined. Parafossarulus striatulus functioned as the first intermediate host which contained M. orientalis DNA, and fishes such as Pseudorasbora parva and Rhodeinae served as the second intermediate hosts with M. orientalis metacercariae in the fish flesh. M. orientalis eggs were found in the feces of three other Swans and six ducks that lived in the ‘Qing’ lake. This was the first reported case about M. orientalis infection of Black Swan. Our study described the course of the infection and provided new information about potential carriers and disseminators of M. orientalis.

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M. orientalis infection was firstly reported in Black Swan in China.

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P. striatulus served as the first intermediate host, P. parva and Rhodeinae as the second intermediate host. •Swans and ducks served as the definitive hosts.

Integrative taxonomy of European parasitic flatworms of the genus Metorchis Looss, 1899 (Trematoda: Opisthorchiidae)

Metorchis spp. are flukes (Platyhelminthes: Digenea) that infect vertebrates, including humans, dogs, cats, poultry and wild game, with cyprinid freshwater fish serving as typical second intermediate hosts. In their definitive hosts, the Metorchis spp. are difficult to identify to species. We provide and analyze sequences of two nuclear (18S rDNA and ITS2) and two mitochondrial (CO1 and ND1) DNA loci of four morphologically identified European species of the Metorchis, namely Metorchis albidus, Metorchis bilis, Metorchis crassiusculus and Metorchis xanthosomus, and of another opisthorchiid, Euamphimerus pancreaticus. DNA analysis suggests that the Metorchis specimens identified morphologically as M. albidus (from Lutra lutra), M. bilis (from Phalacrocorax carbo) and M. crassiusculus (from Aquila heliaca and Buteo rufinus) represent a single species. Thus, M. albidus (Braun, 1893) Loos, 1899 and M. crassiusculus (Rudolphi, 1809) Looss, 1899 are recognized as junior subjective synonyms of M. bilis (Braun, 1790) Odening, 1962. We also provide comparative measurements of the Central European Metorchis spp., and address their tissue specificity and prevalence based on the examination of extensive bird cohort from 1962 to 2015. M. bilis and M. xanthosomus can be morphologically diagnosed by measuring the extent of genitalia relative to body length and by the size ratio of their suckers. They also differ in their core definitive hosts, with ducks (Anas, Aythya) and coots (Fulica) hosting M. xanthosomus, and cormorants (Phalacrocorax), the birds of prey (Buteo, Aquila, etc.), piscivorous mammals (Lutra, Vulpes, Ursus, etc.) and humans hosting M. bilis. Previous reports on the Metorchis spp. contain numerous suspected misidentifications.

The complete mitochondrial genome of Metorchis orientalis (Trematoda: Opisthorchiidae): Comparison with other closely related species and phylogenetic implications

Metorchis orientalis (Trematoda: Opisthorchiidae) is an important trematode infecting many animals and humans, causing metorchiasis. In the present study, the complete mitochondrial (mt) genome of M. orientalis was sequenced. The complete mt genome of M. orientalis is 13,834 bp circular DNA molecule and contains 12 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes. The gene content and arrangement of M. orientalis is the same as those of Opisthorchiidae trematodes (Opisthorchis viverrini, Opisthorchis felineus and Clonorchis sinensis), but distinct from Schistosoma spp. Phylogenetic analyses using concatenated amino acid sequences of 12 protein-coding genes with three different computational algorithms (Bayesian inference, maximum likelihood and maximum parsimony) revealed that M. orientalis and O. viverrini represent sister taxa. The mt genome provides a novel genetic marker for further studies of the identification, classification and molecular epidemiology of Opisthorchiidae trematodes, and should have implications for the diagnosis, prevention and control of metorchiasis in animals and humans.