Fish-borne zoonoses are emerging worldwide, and although most human cases remain confined to tropical regions, particularly Southeast and East Asia, a few cases have been reported in Europe. This review summarizes published and new data on the life cycle of Metagonimus romanicus (misidentified as M. yokogawai, a human pathogen common in East Asia), a heterophyid trematode and one of the potentially fish-borne parasites in Europe. Metagonimus romanicus is distributed from the middle Danube in Central Europe (Slovakia) to eastern Ukraine (including the rivers of the Black Sea basin). Its distribution area coincides with that of its first intermediate hosts, the melanopsid snails Microcolpia daudebartii acicularis and Esperiana esperi. While M. romanicus most likely has a strict specificity for its first snail hosts, metacercariae are generalists and have been detected in over 50 freshwater fish species from 18 families, especially leuciscids. Despite its wide distribution and frequent occurrence in freshwater fish, the zoonotic potential of M. romanicus appears to be low. This is probably due to the exclusive localization of the metacercariae in the fish scales rather than musculature, as well as the rare consumption of raw or undercooked fish in Europe. However, some risk remains and a small number of undiagnosed human infections due to accidental ingestion of scales during the preparation and cleaning of fish cannot be ruled out.

• Keywords
• Cercariae, Europe, Fish, Freshwater, Metacercariae, Snails,
• Publication type
• Journal Article MeSH

Cercariae, the free-living larval stages of trematodes, have adopted an amazing variety of transmission strategies. One of them is prey-mimetism, i.e. cercariae mimicking prey to attract motile hosts to be eaten. In a period between 2002 and 2019, we examined small planorbid snails, Bathyomphalus contortus, Gyraulus parvus and Planorbis planorbis from lakes in Finland and Iceland and from the Curonian Lagoon in Lithuania. Cercariae with conspicuously enlarged tails and unusual swimming behaviour, likely mimicking invertebrate prey, were detected and studied by the use of morphological and molecular (cox1, ITS1-5.8S-ITS2 and 28S rDNA) methods. Cercariae of two species belonging to the genus Apatemon (Strigeidae) were recognised. We consider Apatemon sp. 5 ex P. planorbis from the Curonian Lagoon identical to Cercaria globocaudata U. Szidat, 1940. Cercariae ex G. parvus from Iceland and ex B. contortus from Finland were conspecific, and we named them Apatemon sp. 6; these cercariae could not be associated with any known species. For the first time, we verified that cercariae of the Bulbocauda group belong to the genus Apatemon. We provide a mini-review on records of furcocercariae of the family Strigeidae with enlarged tails reported in freshwaters of the northern hemisphere and reveal that it is not only Apatemon but also Australapatemon and most likely Strigea which belong to the Bulbocauda group, rendering it a purely ecological assemblage. Understanding which invertebrate swimming behaviour these cercariae are mimicking will enhance our knowledge of the processes behind trematode transmission and will help to assess evolutionary pathways of host-finding strategies in trematodes.

• Keywords
• Behaviour, Digenea, Europe, Freshwater, Nuclear and mitochondrial DNA, Trematoda,
• MeSH
• Cercaria genetics   MeSH
• Snails MeSH
• Lakes MeSH
• Trematoda * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH

The biodiversity of freshwater ecosystems globally still leaves much to be discovered, not least in the trematode parasite fauna they support. Echinostome trematode parasites have complex, multiple-host life-cycles, often involving migratory bird definitive hosts, thus leading to widespread distributions. Here, we examined the echinostome diversity in freshwater ecosystems at high latitude locations in Iceland, Finland, Ireland and Alaska (USA). We report 14 echinostome species identified morphologically and molecularly from analyses of nad1 and 28S rDNA sequence data. We found echinostomes parasitising snails of 11 species from the families Lymnaeidae, Planorbidae, Physidae and Valvatidae. The number of echinostome species in different hosts did not vary greatly and ranged from one to three species. Of these 14 trematode species, we discovered four species (Echinoparyphium sp. 1, Echinoparyphium sp. 2, Neopetasiger sp. 5, and Echinostomatidae gen. sp.) as novel in Europe; we provide descriptions for the newly recorded species and those not previously associated with DNA sequences. Two species from Iceland (Neopetasiger islandicus and Echinoparyphium sp. 2) were recorded in both Iceland and North America. All species found in Ireland are new records for this country. Via an integrative taxonomic approach taken, both morphological and molecular data are provided for comparison with future studies to elucidate many of the unknown parasite life cycles and transmission routes. Our reports of species distributions spanning Europe and North America highlight the need for parasite biodiversity assessments across large geographical areas.

TITLE: Diversité des Échinostomes (Digenea, Echinostomatidae) chez leurs hôtes mollusques aux latitudes élevées. ABSTRACT: La biodiversité des écosystèmes d’eau douce à l’échelle mondiale laisse encore beaucoup à découvrir, notamment dans la faune parasitaire des trématodes qu’ils abritent. Les parasites trématodes Échinostomes ont des cycles de vie complexes à hôtes multiples impliquant souvent des oiseaux migrateurs comme hôtes définitifs, conduisant ainsi à des distributions étendues. Ici, nous avons examiné la diversité des échinostomes dans les écosystèmes d’eau douce à des latitudes élevées en Islande, Finlande, Irlande et en Alaska (États-Unis). Nous rapportons de séquences de nad1 et d’ADNr 28S morphologiquement et moléculairement à partir d’analyses de données de séquence d’ADNr nad1 et 28S. Nous avons trouvé des échinostomes parasitant les mollusques de 11 espèces des familles Lymnaeidae, Planorbidae, Physidae et Valvatidae. Le nombre d’espèces d’échinostomes dans différents hôtes ne variait pas beaucoup et allait d’une à trois espèces. Sur ces 14 espèces de trématodes, nous avons découvert quatre espèces (Echinoparyphium sp. 1, Echinoparyphium sp. 2, Neopetasiger sp. 5, Echinostomatidae gen. sp.) comme nouvelles pour l’Europe; nous fournissons des descriptions pour les espèces nouvellement signalées et celles qui n’étaient pas précédemment associées à des séquences d’ADN. Deux espèces d’Islande (Neopetasiger islandicus et Echinoparyphium sp. 2) ont été signalées en Islande et en Amérique du Nord. Toutes les espèces trouvées en Irlande sont de nouveaux signalements pour ce pays. Grâce à une approche taxonomique intégrative, des données morphologiques et moléculaires sont fournies à des fins de comparaison avec des études futures afin d’élucider les nombreux cycles de vie et voies de transmission des parasites, qui sont inconnus. Nos données sur la répartition des espèces en Europe et en Amérique du Nord soulignent la nécessité d’évaluer la biodiversité des parasites dans de vastes zones géographiques.

• Keywords
• Europe, Mitochondrial and nuclear DNA, Mollusca, Morphology, North America, Trematoda,
• MeSH
• Echinostomatidae * genetics   MeSH
• Ecosystem MeSH
• Snails MeSH
• Humans MeSH
• Trematoda * MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Europe MeSH
• North America MeSH

Human cercarial dermatitis is a parasitic disease that causes an allergic reaction in the skin (swimmer's itch) as a consequence of contact with cercariae of bird schistosomes present in water, mainly of the genus Trichobilharzia Skrjabin et Zakarow, 1920. The main objective of the study was to confirm the presence of the zoonotic disease agent following reports of human infections in recreational water in Slovakia. We identified two species of freshwater snails at Košice Lake, Radix auricularia (Linnaeus, 1758) and Physa acuta (Draparnaud, 1805). Trematode infections were observed only in R. auricularia. Of the 62 snails collected, 11 (17.7%) were infected with 5 different species of larval stages of trematodes. The blood fluke Trichobilharzia franki was found in 2 (3.2%) of the examined snails. The present record provides the first evidence that T. franki from the pulmonate snail R. auricularia represents a source of human cercarial dermatitis in recreational water in Slovakia. Our finding complements the easternmost records of both swimmer's itch and the confirmed occurrence of a bird schistosome in a waterbody in Europe. The present work suggests that the health risks associated with trichobilharziasis need to be further studied by detailed monitoring of the occurrence of the major causative agent of human cercarial dermatitis, T. franki.

• Keywords
• Bird schistosomes, Cercariae, Cercarial dermatitis, Trematodes, Trichobilharzia, Zoonosis,
• MeSH
• Dermatitis epidemiology   parasitology   MeSH
• Disease Outbreaks MeSH
• Snails parasitology   MeSH
• Trematode Infections epidemiology   parasitology   transmission   MeSH
• Lakes parasitology   MeSH
• Humans MeSH
• Skin Diseases, Parasitic parasitology   transmission   MeSH
• Schistosomatidae classification   genetics   isolation & purification   MeSH
• Schistosomiasis epidemiology   parasitology   transmission   MeSH
• Zoonoses epidemiology   parasitology   transmission   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Slovakia epidemiology   MeSH

Parasites comprise a huge part of the biodiversity on earth. However, on a local scale, not much is known about their diversity and community structure. Here, we assess the diversity of larval trematode communities in an interconnected freshwater system of the River Ruhr in Germany and analyse how the parasites are spatially and temporally distributed in the ecosystem. A total of 5347 snail hosts belonging to six species revealed a highly diverse parasite fauna with 36 trematode species. More abundant snail species harboured more species-rich trematode faunas and communities, with the two dominant snail species, Radix auricularia and Gyraulus albus, accounting for almost 90% of the trematode diversity and harbouring spatially and temporally stable parasite communities. The results highlight the important role of stable keystone host populations for trematode transmission, structure and diversity. This local trematode diversity reveals information on definitive host occurrence and trophic interactions within ecosystems.

• MeSH
• Biodiversity * MeSH
• Ecosystem * MeSH
• Snails parasitology   MeSH
• Host-Parasite Interactions genetics   MeSH
• Larva parasitology   MeSH
• Humans MeSH
• Population Dynamics MeSH
• Rivers MeSH
• Fresh Water parasitology   MeSH
• Trematoda classification   pathogenicity   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Germany MeSH

In freshwater ecosystems, snails can significantly influence the competition between primary producers through grazing of periphyton. This activity can potentially be modified by trematodes, a large group of parasites which mostly use molluscs as the first intermediate host. Available studies, however, show contradictory effects of trematodes on snail periphyton grazing. Here, we used four different freshwater snail-trematode systems to test whether a general pattern can be detected for the impact of trematode infections on snail periphyton grazing. In our experimental systems, mass-specific periphyton grazing rates of infected snails were higher, lower, or similar to rates of non-infected conspecifics, suggesting that no general pattern exists. The variation across studied snail-trematode systems may result from differences on how the parasite uses the resources of the snail and thus affects their energy budget. Trematode infections can significantly alter the grazing rate of snails, where, depending on the system, the mass-specific grazing rate can double or halve. This underlines both, the high ecological relevance of trematodes and the need for comprehensive studies at the species level to allow an integration of these parasite-host interactions into aquatic food web concepts.

• Keywords
• Freshwater snails, Grazing rates, Host–parasite interaction, Periphyton, Trematodes,
• MeSH
• Ecology MeSH
• Ecosystem MeSH
• Snails parasitology   MeSH
• Trematode Infections parasitology   MeSH
• Host-Parasite Interactions physiology   MeSH
• Periphyton * MeSH
• Food Chain MeSH
• Eating physiology   MeSH
• Fresh Water parasitology   MeSH
• Trematoda isolation & purification   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH

In contrast to the well-studied trematode fauna of lymnaeid snails, only little is known about the role of small planorbid snails as first intermediate hosts for trematodes in temperate freshwater systems. This study aims at closing this gap by assessing the diversity and composition of larval trematode communities in Gyraulus albus and Segmentina nitida in a Central European reservoir system, and by providing an updated comprehensive review of the published trematode records of these snail hosts. A total of 3691 planorbid snails (3270 G. albus; 421 S. nitida) was collected in three consecutive years from four reservoirs of the River Ruhr catchment area in Germany. Gyraulus albus showed a higher overall trematode prevalence (11.7%) and more diverse trematode fauna (12 species) compared to S. nitida, which harboured three species and showed a lower trematode prevalence (1.7%). Altogether, 13 trematode species belonging to four families were identified in both hosts. Seven trematode species encountered in this study represent novel records for these hosts, and/or constitute first records of these larval stages from Germany. Trematode component communities in G. albus were stable across seasons and years, indicating excellent conditions for trematodes in this snail host and the continuous presence of the final hosts of the most dominant trematode species. Overall, this study reveals the importance of small planorbid snails, in particular G. albus, as first intermediate hosts for a species-rich trematode fauna in European freshwater systems, and highlights the parasites' contribution to the ecosystem's biodiversity.

• Keywords
• Community composition, Digenea, Europe, Parasite diversity, Planorbidae, Reservoir,
• MeSH
• Biodiversity * MeSH
• Ecosystem MeSH
• Snails parasitology   MeSH
• Trematode Infections parasitology   veterinary   MeSH
• Larva MeSH
• Rivers MeSH
• Seasons MeSH
• Fresh Water MeSH
• Trematoda physiology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Germany epidemiology   MeSH

We report digeneans (Diplostomidae, Crassiphialinae) in the endangered freshwater fishes Valencia letourneuxi and Valencia robertae, endemics of Western Greece. Digenean metacercariae occurred in two forms in the abdominal cavity, excysted and encysted, the latter attached to the gonads, liver and alimentary tract. Parasites were, using morphological and molecular techniques, identified as two representatives of Crassiphialinae, specifically part of the Posthodiplostomum-Ornithodiplostomum clade. The spatial, seasonal, and age class variation in parasite prevalence was examined. Autumn parasite prevalence varied between the six populations sampled (18.2 to 100%). Seasonal prevalence at the two sites sampled quadannually peaked in autumn and reached its lowest value in spring; prevalence increased with size to 100% in young adult fish. We did not find a correlation between prevalence and host sex. Overall parasites' weight averaged 0.64% of the host's, while parasite weight increased with host weight. A comparison of relative condition and hepatosomatic and gonadosomatic indices of infected and metacercariae-free specimens showed that infection did not have a significant effect on host body condition and reproduction. Regarding the parasite's life cycle, planorbid gastropods are proposed as potential first intermediate hosts in view of the host's diet and occurrence data of molluscs in the ecosystem. This is the first record of a diplostomid digenean in valenciid fishes and of representatives of the Posthodiplostomum-Ornithodiplostomum clade in a native Greek freshwater fish. Our findings are discussed in conjunction to fish conservation interventions, since parasites may contribute to the decline of endangered species.

• Keywords
• Digenea, Host body condition, Parasite prevalence, Planorbidae, Platyhelminthes, Valenciidae,
• MeSH
• Killifishes parasitology   MeSH
• Ecosystem MeSH
• Trematode Infections parasitology   veterinary   MeSH
• Mollusca parasitology   MeSH
• Metacercariae * MeSH
• Fish Diseases parasitology   MeSH
• Endangered Species MeSH
• Fresh Water MeSH
• Life Cycle Stages MeSH
• Trematoda classification   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Greece MeSH

We analysed two novel databases containing 2,380 and 8,202 host-parasite-locality records for trematode parasites of molluscs and fishes, respectively, to assess the biodiversity of trematodes in their intermediate mollusc and fish hosts in the freshwater environment in Europe. The "mollusc" dataset covers large numbers of pulmonate (29 spp.), "prosobranch" (15 spp.) and bivalve (11 spp.) molluscs acting as first intermediate hosts for 171 trematode species of 89 genera and 35 families. Of these, 23 and 40 species utilise freshwater fishes as definitive and second intermediate hosts, respectively. The most frequently recorded families are the Echinostomatidae Looss, 1899, Diplostomidae Poirier, 1886 and Schistosomatidae Stilles & Hassal, 1898, and the most frequently recorded species are Diplostomum spathaceum (Rudolphi, 1819), D. pseudospathaceum Niewiadomska, 1984 and Echinoparyphium recurvatum (von Linstow, 1873). Four snail species harbour extremely rich trematode faunas: Lymnaea stagnalis (L.) (41 spp.); Planorbis planorbis (L.) (39 spp.); Radix peregra (O.F. Müller) (33 spp.); and R. ovata (Draparnaud) (31 spp.). The "fish" dataset covers 99 fish species of 63 genera and 19 families acting as second intermediate hosts for 66 species of 33 genera and nine families. The most frequently recorded families are the Diplostomidae Poirier, 1886, Strigeidae Railliet, 1919 and Bucephalidae Poche, 1907, and the most frequently recorded species are Diplostomum spathaceum (Rudolphi, 1819), Tylodelphys clavata (von Nordmann, 1832) and Posthodiplostomum cuticola (von Nordmann, 1832). Four cyprinid fishes exhibit the highest species richness of larval trematodes: Rutilus rutilus (L.) (41 spp.); Abramis brama (L.) (34 spp.); Blicca bjoerkna (L.) (33 spp.); and Scardinius erythrophthalmus (L.) (33 spp.). Larval stages of 50 species reported in fish are also reported in freshwater molluscs, thus indicating a relatively good knowledge of the life-cycles of fish trematodes in Europe. We provide host-parasite lists for 55 species of molluscs with a European distribution comprising 413 host-parasite associations.

• MeSH
• Biodiversity * MeSH
• Ecosystem * MeSH
• Larva MeSH
• Mollusca parasitology   MeSH
• Fishes parasitology   MeSH
• Trematoda classification   physiology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Geographicals
• Europe MeSH

Species of Echinostoma Rudolphi, 1809 (Digenea: Echinostomatidae) belonging to the 'revolutum' species complex were re-examined based on material gathered in an extensive sampling programme in eight countries in Europe. The morphology of the life-cycle stages was studied in naturally and experimentally infected snail and bird hosts. A review, with an updated synonymy, is presented for six European species, including one new to science, i.e. Echinostoma revolutum (Frölich, 1802) (sensu stricto) (type-species), E. bolschewense (Kotova, 1939), E. miyagawai Ishii, 1932, E. nasincovae n. sp., E. paraulum Dietz, 1909 and Echinostoma sp. IG), and keys to the identification of their cercariae and adults are provided.

• MeSH
• Biodiversity * MeSH
• Species Specificity MeSH
• Echinostoma classification   cytology   physiology   MeSH
• Snails parasitology   MeSH
• Host-Parasite Interactions MeSH
• Birds parasitology   MeSH
• Life Cycle Stages MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Europe MeSH