Cercariae are motile infectious larval stages of digenetic trematodes that emerge from their molluscan first intermediate host to seek the next host in their life cycle. A crucial transmission strategy of trematodes involves releasing the maximum number of cercariae at times that coincide with the presence and activity of the next hosts, thereby increasing the likelihood of successful infection and continuation of the parasite's life cycle. We investigated the cercarial emergence of two furcocercous (with forked tail) trematodes Tylodelphys clavata (von Nordmann, 1832) and unidentified species of Sanguinicola Plehn, 1905 from naturally infected Ampullaceana balthica (Linnaeus) and Radix auricularia (Linnaeus) snails under natural light and constant temperature conditions. Both trematodes, which are important fish pathogens, showed distinct daily emergence rhythms influenced by light intensity, with emergence peaking at sunset and night for T. clavata and at night for Sanguinicola sp. The daily emergence rhythms of T. clavata cercariae were consistent in both summer and autumn, indicating adaptability to natural changes in seasonal photoperiods. The interspecific differences in emergence patterns are likely related to the behavioural patterns of upstream, i.e., next in the life cycle, fish hosts. Cercarial output also varied between trematode species and seasons, likely due to combined effects of snail size, intensity of trematode infection in snails and size of cercariae rather than seasonal temperatures. The trematodes were molecularly characterised using mitochondrial (cox1) and nuclear (28S rDNA and ITS1-5.8S-ITS2) regions to confirm their identity and facilitate future studies. This study highlights the importance of light-regulated and host-synchronised cercarial emergence rhythms for increased trematode transmission success and reveals significant variation in cercarial output influenced by environmental and biological factors, contributing to a deeper understanding of trematode ecology and disease management.

• Keywords
• DNA, Sanguinicola sp., Tylodelphys clavata, cercariae, snails, transmission,
• MeSH
• Cercaria physiology   MeSH
• Snails * parasitology   MeSH
• Host-Parasite Interactions MeSH
• Seasons MeSH
• Light MeSH
• Trematoda * physiology   genetics   classification   growth & development   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 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

Digenean trematodes are common and abundant in aquatic habitats and their free-living larvae, the cercariae, have recently been recognized as important components of ecosystems in terms of comprising a significant proportion of biomass and in having a potentially strong influence on food web dynamics. One strategy to enhance their transmission success is to produce high numbers of cercariae which are available during the activity peak of the next host. In laboratory experiments with 13 Lymnaea stagnalis snails infected with Trichobilharzia szidati the average daily emergence rate per snail was determined as 2,621 cercariae, with a maximum of 29,560. During a snail's lifetime this summed up to a mass equivalent of or even exceeding the snail's own body mass. Extrapolated for the eutrophic pond where the snails were collected, annual T. szidati biomass may reach 4.65 tons, a value equivalent to a large Asian elephant. Emission peaks were observed after the onset of illumination, indicating emission synchronizing with the high morning activities of the definitive hosts, ducks. However, high cercarial emission is possible throughout the day under favorable lightning conditions. Therefore, although bird schistosomes, such as T. szidati constitute only a fraction of the diverse trematode communities in the studied aquatic ecosystem, their cercariae can still pose a considerable risk for humans of getting cercarial dermatitis (swimmer's itch) due to the high number of cercariae emitted from infected snails.

• MeSH
• Biomass MeSH
• Cercaria growth & development   MeSH
• Chronobiology Phenomena MeSH
• Ecosystem MeSH
• Lymnaea parasitology   physiology   MeSH
• Statistics, Nonparametric MeSH
• Swimming MeSH
• Schistosomatidae growth & development   MeSH
• Life Cycle Stages MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Cercarial dermatitis (swimmer's itch) is a condition caused by infective larvae (cercariae) of a species-rich group of mammalian and avian schistosomes. Over the last decade, it has been reported in areas that previously had few or no cases of dermatitis and is thus considered an emerging disease. It is obvious that avian schistosomes are responsible for the majority of reported dermatitis outbreaks around the world, and thus they are the primary focus of this review. Although they infect humans, they do not mature and usually die in the skin. Experimental infections of avian schistosomes in mice show that in previously exposed hosts, there is a strong skin immune reaction that kills the schistosome. However, penetration of larvae into naive mice can result in temporary migration from the skin. This is of particular interest because the worms are able to migrate to different organs, for example, the lungs in the case of visceral schistosomes and the central nervous system in the case of nasal schistosomes. The risk of such migration and accompanying disorders needs to be clarified for humans and animals of interest (e.g., dogs). Herein we compiled the most comprehensive review of the diversity, immunology, and epidemiology of avian schistosomes causing cercarial dermatitis.

• MeSH
• Biodiversity MeSH
• Disease Outbreaks MeSH
• Host Specificity MeSH
• Humans MeSH
• Bird Diseases parasitology   transmission   MeSH
• Skin Diseases, Parasitic epidemiology   immunology   parasitology   prevention & control   MeSH
• Birds MeSH
• Schistosomiasis epidemiology   immunology   parasitology   prevention & control   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Larval stages of Plagiorchis spp. are both ubiquitous and ecologically important parasites in snail populations of freshwater ecosystems in Europe. However, difficulties in distinguishing the morphologically similar cercariae used for species identification, may lead to underestimation of species diversity. In this study, 38 isolates of Plagiorchis spp. infecting two lymnaeid snails, Lymnaea stagnalis (L.) and Radix auricularia (L.), in five central European freshwater ecosystems were subjected to morphological and molecular assessment. Five morphologically homogeneous and genetically distinct lineages of Plagiorchis spp. were identified via matching molecular data for the mitochondrial cytochrome c oxidase subunit I (cox1) gene with detailed morphological and morphometric data of the cercariae. Comparative sequence analysis using partial 28S rDNA and ITS1-5.8S-ITS2 sequences revealed that three distinct cox1 lineages are conspecific with Plagiorchis elegans (Rudolphi, 1802), P. maculosus (Rudolphi, 1802) and P. koreanus Ogata, 1938, respectively, whereas the lineage identified based on cercarial morphology as P. neomidis Brendow, 1970 plus a single isolate that could not be assigned to a described species, did not match any of the available sequences for Plagiorchis spp. A key to the cercariae of Plagiorchis spp. parasitising lymnaeid populations in central Europe is provided to facilitate identification.

• MeSH
• Biodiversity * MeSH
• Cercaria cytology   MeSH
• Species Specificity MeSH
• Phylogeny * MeSH
• Snails parasitology   MeSH
• DNA, Ribosomal Spacer genetics   MeSH
• Molecular Sequence Data MeSH
• Electron Transport Complex IV genetics   MeSH
• RNA, Ribosomal, 28S genetics   MeSH
• RNA, Ribosomal, 5.8S genetics   MeSH
• Sequence Homology, Nucleic Acid MeSH
• Fresh Water * MeSH
• Trematoda * anatomy & histology   classification   genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Europe MeSH
• Names of Substances
• DNA, Ribosomal Spacer MeSH
• Electron Transport Complex IV MeSH
• RNA, Ribosomal, 28S MeSH
• RNA, Ribosomal, 5.8S MeSH