Anurans are bioindicators and key components of ecosystem functions. Although South America harbors more than 4,000 identified anuran species, fewer than 10% have been analyzed regarding their trematode fauna. When tadpoles are considered, the paucity of studies becomes even more evident. Considering the ability of digeneans to serve as indicators of ecosystem health, it is evident that there is a gap in the knowledge of trematodes occurring in anuran biodiversity hotspots. Herein, we provide an ecological and morphological analysis of the trematode component community recovered in tadpoles and adult anurans. During a long-term herpetological and helminthological study conducted in a Cerrado fragment in Brazil, 569 anurans from 17 species were necropsied. Eleven species were common to both adults and tadpoles, and six species occurred only in adults. The total prevalence was 61% (352/569), in separate analyses, 65% (192/296) for adult anurans, and 58% (160/273) for tadpoles. A total of 12,397 trematodes belonging to 16 taxa were recovered. The component community was composed mostly of metacercariae. We provided a brief morphological description for each trematode taxa recovered. Additionally, statistical analysis was performed to elucidate the differences between tadpoles and adult anurans trematode communities. The trematode community analyzed in our study revealed 24 new host records and was the first to include tadpoles in such an analysis, highlighting the importance of faunistic inventories for a better understanding of parasitism in their hosts, as well as providing a foundation for further research.

Nematode records and specimens from the South Australian Museum, Australian Museum, CSIRO Wildlife Collection, Queensland Museum, Western Australian Museum, and Natural History Museum, London, of 1107 individuals of Rattus fuscipes were examined. The nematode community comprised 19 families, 36 genera, and 44 identified species. Mastophorus muris and unidentified heligmonellids were recovered from 4 individuals of R. f. fuscipes. Rattus f. assimilis was infected with 40 identified species of nematode from 955 individuals; R. f. coracius 18 species from 107 individuals; and R. f. greyii 8 species from 28 individuals. Rattus fuscipes harboured 18 species in Northern Queensland, 27 species in Southern Queensland, 27 species in New South Wales, 19 species in Victoria, and 8 species in South Australia. A bootstrap analysis of the R. f. greyii nematode community indicated that 91.3% of species had been found. No core species were revealed. The Trichostrongylidae dominated with Nippostrongylus magnus, and Odilia emanuelae occurring in all the populations. Nippostrongylus magnus, 43% prevalence, in Victoria and Physaloptera troughtoni, 42% prevalence, in South Australia were secondary species. Sorensen’s indices indicated that R. f. assimilis and R. f. coracius had the most similar nematode communities, 54.8%. Overall, the Northern and Southern Queensland populations were most similar (77.3%) and the New South Wales and South Australian populations least similar (22.9%). The identifications of Heterakis spumosa, Physaloptera troughtoni, Rictularia mackerrasae, and Pterygodermatites pearsoni were confirmed. The species composition of the nematode community of R. fuscipes suggested a scenario of coevolution, host switching, recently acquired and occasional infections in a community of cosmopolitan, regional, and indigenous species. Species throughout the component communities of R. fuscipes indicated that climate and habitat were also determinants of species composition.

It is assumed that the biology and ecology of commercial fish species are relatively well-known, given that many of these parameters are key for stock assessment in fisheries management. Surprisingly (or not), several new parasite species are described annually from fish that are of commercial and cultural importance. Haddock (Melanogrammus aeglefinus) is an important commercial fish species in the North Atlantic with more than 50 parasite species having been reported from it. Despite its commercial importance in Icelandic waters, only 11 parasite species have been reported from Icelandic haddock. In February and March 2023, 26 haddock were sampled, including 16 and 10 from the north and south of Iceland, respectively. Fish were examined for parasites, with a focus on macroparasites (large, usually visible to the eye). Parasites were identified morphologically with identifications of helminths confirmed using DNA barcoding (Sanger sequencing). Overall, 19 different parasite species were recovered with 17 being shared between haddock sampled from the north and south of Iceland. Of these, eight represent new geographical records for parasites of haddock in Icelandic waters. Our study indicates that monitoring for parasites remains important, regardless of how well a species has been studied. Furthermore, reporting parasites per organ and per region, especially when areas are known to be influenced by different abiotic and physical features, is important in the context of parasites as biological tags for stock identification. Despite a small sample size, our study suggests that some parasites might act as potential biological tags for stock identification of haddock in Icelandic waters.

Notocotylidae is a family of digeneans with some aberrant morphological features (absence of ventral sucker), which as sexual adults parasitise herbivorous and molluscivorous birds and mammals. The phylogenetics and taxonomy of this family have many unresolved problems concerning the relatedness of genera and species and the reliability of identification of specimens for which molecular data are available. The aim of this study is morphological and molecular characterisation of the type species of Notocotylus Diesing, 1839 (Notocotylus triserialis Diesing, 1839) and its two congeners, Notocotylus pacifera (Noble, 1933) and Notocotylus sp., and verification of the monophyly of the genus Notocotylus within the taxonomic boundaries established in the recent revision. Notocotylus triserialis was collected from a Greater White-fronted Goose Anser albifrons (Scopoli, 1769) taken down in the Russian Karelia, and the other two digenean species were derived from European Coots Fulica atra Linnaeus, 1758, from different locations in Eurasia (Eastern Europe and the Far East). We provide detailed morphological descriptions of the examined digeneans, supplemented with original line drawings. Notocotylus sp. is morphologically similar to N. pacifera but differs in cirrus sac length. Phylogenetic inference based on the 28S rRNA gene dataset places N. triserialis within a well-supported clade comprising several congeners, whereas N. pacifera is recovered outside this assemblage, forming a closer phylogenetic association with Pseudocatatropis dvoryadkini Izrailskaia, Besprozvannykh, Tatonova, Nguyen and Ngo, 2019. Thus, our data do not support the monophyly of the genus Notocotylus.

Trichinella spiralis (T. spiralis) is a zoonotic parasitic worm that has a significant impact on both public health and the livestock industry. It is widely used in experimental studies because of several unique features of its life cycle that can be completed in a single host, including distinct intestinal and muscular phases of infection, and it can be easily maintained in laboratory animals. These characteristics make T. spiralis a valuable model for evaluating the efficacy of new drugs and vaccines against parasitic infections. The current work aims to evaluate the procedures used for Trichinella larval counting in experimental studies by comparing the magnetic stirring digestion method (MSDM) with individual muscle digestion and compression techniques under standardised, controlled conditions to assess their effectiveness and applicability. Fifteen male Swiss albino mice were orally infected with T. spiralis and sacrificed on day 35 post-infection. They were divided into three groups: group 1—MSDM for total larval count; group 2—individual digestion of masseter, diaphragm, gastrocnemius, and tongue muscles; and group 3—slide compression method of the same muscles. MSDM yielded the highest larval counts, with individual muscle digestion and compression methods generally producing significantly lower results, except tongue digestion, while correlation and concordance analyses identified gastrocnemius compression as an alternative despite overall poor agreement with the reference method. Therefore, MSDM is the most accurate method for larval counting in experimental studies, compared to individual muscle digestion or compression methods.

Schwartzitrema Vigueras, 1941, is a small, rarely reported genus of diplostomoideans that parasitize avian definitive hosts, predominantly anhingas, on several continents. No DNA sequences were previously available for any Schwartzitrema spp. In the present study, we describe adults of 2 new Schwartzitrema spp. from anhingas in Brazil. We also provide description of metacercaria of one of the new species from Argentina. Schwartzitrema macrotesticulata n. sp. lacks a clear separation between its testes, appearing almost as a contiguous, irregularly shaped, lobular mass. A highly characteristic feature of Schwartzitrema macroholdfastus n. sp. is a strongly enlarged lobe of the holdfast organ. These features, along with distribution of vitellarium and nature of the preputial folds surrounding the genital cones, separate the new species from their congeners. We generated partial sequences of the large ribosomal subunit (28S) rDNA and cytochrome c oxidase subunit I (cox1) mtDNA genes from adult forms of both species and cox1 of metacercarial stages. The 28S sequences were used for phylogenetic inference. The pairwise sequence divergence between the 2 species is 4.0–4.6% in cox1 gene. Intraspecific variability in the same cox1 region did not exceed 0.8% despite the long geographic distance between collecting sites in Brazil and Argentina.

Species of the genus Rauschiella are trematodes of frogs and snakes in the Americas. The taxonomy of the group is complex, and most of the 18 currently valid species are known only from the original description. Moreover, genetic data are available only for two North American species (Rauschiella tineri and Rauschiella poncedeleoni). In this context, integrative taxonomy studies are necessary for Rauschiella spp. found in South America. Herein, during a long-term herpetological and helminthological study conducted in Selvíria, Mato Grosso do Sul, Brazil, between 2016 and 2019, 296 anurans from 17 species were necropsied. A plagiorchioid trematode found in the intestine of 7/12 Leptodactylus macrosternum, 10/106 Leptodactylus podicipinus, and 13/20 Pseudis platensis was subject to morphological and molecular characterisation. Samples of the trematodes were studied by optical and scanning electron microscopies and identified as Rauschiella proxima (Freitas, 1941), here reported in new anuran hosts and geographical area. Sequences of the nuclear gene 28S rDNA (1148 bp) were generated and subjected to phylogenetic analysis. Our isolates of R. proxima from Brazil grouped in a well-supported clade with R. poncedeleoni and R. tineri, and genetic divergences to these species were low (0.45% and 0.54%, respectively), supporting the congeneric status among them. However, the addition of a South American representative of Rauschiella and the construction of more comprehensive phylogenetic analyses, including 78 plagiorchioid species from 15 families, did not result in advances concerning the familial level of classification of this genus, which remains as incertae sedis in the superfamily Plagiorchoidea.

The genus Aphelenchoides Fischer, 1894, encompasses nearly 200 species with significant ecological and economic importance, yet its taxonomy remains complex due to morphological similarities among species and limited molecular data. In this study, we describe a new species, Aphelenchoides vinhphucensis sp. n., collected from the rhizosphere of rice (Oryza sativa L.) in Vinh Phuc Province, Vietnam. The new species is distinguished by its morphological characteristics, including a slender stylet (9.6–12.7 μm), distinct lateral fields with four lines, a conical tail with a pointed mucro, and a well-developed post-uterine sac. Males feature three pairs of caudal papillae and arcuate spicules. Scanning electron microscopy provided detailed insights into surface features, complementing light microscopy observations. Molecular analyses of the D2-D3 regions of 28S rRNA and 18S rRNA supported the distinct phylogenetic placement of Aphelenchoides vinhphucensis sp. n., differentiating it from closely related species. Bayesian phylogenetic analysis confirmed its divergence, contributing to our understanding of biodiversity of the genus Aphelenchoides. This integrative approach highlights the importance of combining classical morphological methods with modern molecular tools for accurate species identification. The discovery of Aphelenchoides vinhphucensis sp. n. underscores the nematode diversity in Vietnam, especially those associated with rice cultivation.

This study presents data on helminth communities from 93 Hooded Crows (Corvus cornix). The dataset includes historical and contemporary records from three localities in Ukraine with different levels of urbanisation: Kyiv, the Middle Dnipro River, and Polissya. Thirty-two helminth species were identified, including 14 trematodes, six cestodes, 11 nematodes, and one acanthocephalan. The nematodes Eufilariella delicata and Hadjelia truncata are documented in Hooded Crows for the first time. During the statistical analysis, it was revealed that the used dataset is insufficient for robust inference regarding the impact of urbanisation on helminth communities due to its temporal and spatial biases. Despite the limitation, the data offer information for future research on the influence of urbanisation on helminth biodiversity in avian hosts.

We report the first identification of nematode parasitism in a nemertean host (Arctostemma arcticum), representing a novel host-parasite interaction in marine ecosystems. Larvae of the anisakid nematode were discovered within the rhynchocoel of A. arcticum collected from the White Sea, suggesting transmission via ingestion of infected crustaceans – a previously undocumented pathway. The nematode was identified as Phocanema bulbosum through both morphological and molecular analyses.

The presence of nematode in nemertean A. arcticum implies trophic transmission through nemertean predation on infected amphipods, supported by hoplonemertean feeding strategy. While some fish occasionally consume nemerteans, their low predation frequency suggests A. arcticum could act as a dead-end host.

This study expands the known host range of Anisakidae, though it remains uncertain whether nemerteans serve as competent hosts in the P. bulbosum life cycle. Nevertheless, the findings highlight the need to assess nemerteans’ potential influence on parasite dynamics in fisheries and aquaculture, particularly where they coexist with intermediate and definitive hosts.

Garra gotyla is a benthopelagic freshwater cyprinid fish native to Asia, valued for both food and ornamental purposes; nevertheless, its parasitic diseases are poorly understood. The present study investigated the presence and ecological indices (prevalence and intensity) of monogenean parasites infecting G. gotyla in Mizoram, northeast India. Additionally, the study aimed to assess the phylogenetic relationships among three closely related dactylogyrid genera: Dactylogyrus, Dogielius, and Dactylogyroides. Monogeneans were initially identified based on the comparative morphology of their sclerotised haptoral and reproductive structures, followed by BLASTn comparisons of their partial 28S rRNA gene sequences. Two dactylogyrid species, Dactylogyrus labro sp. n. and Dogielius salpinx sp. n., were recovered and are described herein as new to science. Dactylogyrus labro was found to infect all examined fish, whereas D. salpinx had a slightly lower prevalence, ranging from 76.5% to 83.3% across different sampling sites. The phylogenetic insights from these species presented in this study highlight the complex evolutionary relationships within these three genera. Further, this study provides the first confirmed molecular data for a Dogielius species, allowing for much-needed phylogenetic studies on the genus and filling a gap in sequencing data for Indian monogeneans. Since all monogeneans are potentially hazardous parasites, more studies are needed to map their diversity and effects on host fishes in this region.

Environmental DNA (eDNA) metabarcoding has lagged in parasite biodiversity assessments. We implemented this method to examine parasite diversity in sediment and water from 4 physically connected aquatic habitats in coastal South Carolina, USA, as part of a ParasiteBlitz in April 2023. Sediment was collected using a syringe corer, and water was sampled using active filtration and passive collection. Five amplicon libraries, using primers targeting portions of the mitochondrial COI of platyhelminths and 18S ribosomal RNA genes of nematodes, myxozoans, microsporidians, and protists, successfully yielded parasite sequences. Out of >5.8 million sequences, we identified >1,000 parasite amplicon sequence variants (ASVs) corresponding to ~600 parasite operational taxonomic units, from 6 parasite groups. Most diversity was observed among the microsporidians, whose assay demonstrated the highest fidelity. Actively-filtered water samples captured ASVs of all 6 groups, whereas sediment captured only 4, despite yielding 3× as many ASVs. Low DNA yields from passive water samples resulted in fewer, but some unique, ASVs representing 3 parasite groups. The most efficient sampling method varied with respect to parasite group across habitats, and the parasite communities from each habitat were distinct regardless of sampling method. We detected ASVs of 9 named species, 4 of which may represent introductions to the US. The abundance of our results demonstrates the effectiveness and efficiency of eDNA metabarcoding for assessing parasite diversity during short, intensive surveys, and highlights the critical need for more comprehensive sequence databases and the development of primers for those parasite taxa that elude detection using eDNA methods.

The yellowfin, Thunnus albacares (Bonaterre), is one of the most important resources for commercial fisheries along the Mexican Pacific coast. The parasite fauna of this important marine resource has been documented in different regions across its global distributional range. However, few studies have been conducted on parasites of tuna populations in the Cortezian Marine Ecoregion (CME) in northwestern Mexico, despite the development of the fresh and frozen sushi/sashimi-grade tuna market in recent decades. Our study aimed at identifying the metazoan parasite fauna of T. albacares in the CME. Between 2023 and 2024, 17 individuals were studied for parasites before being processed. Parasites were collected and identified using morphological and molecular data. One hundred twenty-five metazoan parasites were collected, representing 10 species, including the monogeneans Hexostoma thynni (Delaroche, 1811) Rafinesque, 1815, Neobenedenia girellae (Hargis, 1955) Yamaguti, 1963, and Capsala sp., the digenean Hirudinella ahi (Pallas, 1774) Baird, 1853, the larval cestode Heterosphyriocephalus tergestinus (Pintner, 1913) Dallarés, Carrassón and Schaeffner, 2016, larval forms of the nematode Anisakis typica (Diesing, 1860) Baylis, 1920, the acanthocephalan Rhadinorhynchus laterospinosus Amin, Heckmann, and Ha, 2011, and three species of copepods, Euryphorus brachypterus (Gerstaecker, 1853), Pseudocycnus appendiculatus Heller, 1865 and Brachiella thynni Cuvier, 1830. Anisakis typica reached the highest prevalence of infection in our samples, and along with R. laterospinosus, it reached the highest mean intensity values. This study reports a species that represents a zoonotic risk (A. typica) and contributes to the understanding of the parasite diversity of commercially important fish in the CME.

Based on morphological and molecular studies, including analysis of variation of four molecular markers, there are two orientocreadiid species, Orientocreadium cf. pseudobagri and O. cf. elegans, in the south of the Russian Far East. Trematodes of these two species possess morphological and molecular variation that is most possibly related to population formation processes for these species in the investigated territory. Our molecular data show that the trematode assemblages studied were subdivided for 28S rDNA markers into two large groups related to basins in different water bodies. Nucleotide sequences of these groups are closely related to each other. Within each group there are specific nucleotide substitutions that are unique for several geographical local samples of trematodes. This variation reflects local processes of divergence of these worms. Results of the median-joining network analysis based on concatenated mitochondrial cox1 and nd1 gene sequences support this inference, showing the existence of four groups of haplotypes of Orientocreadium trematodes that are associated with geographical locations.

This study investigates the endohelminth parasites of three-spined stickleback, Gasterosteus aculeatus, across marine, anadromous, and freshwater populations in the White Sea (Russia). A total of 241 sticklebacks were collected in Velikaya Salma Strait during 2022–2024. Thirteen helminth species were identified using morphological and molecular methods. Genetic analysis confirmed the presence of Anisakis simplex sensu stricto, Hysterothylacium aduncum, Phyllodistomum folium, Brachyphallus crenatus, and Alloopistholecithum cf. salmonis. We identified variability in parasite communities between 2022+2023 and 2024 both within and between marine, anadromous and freshwater host populations. The most striking temporal changes were observed in the parasite communities of the anadromous stickleback population, which is probably due to the different periods of time spent by the fish in fresh water in the years studied. This study highlights differences in infection of marine, anadromous, and freshwater populations of three-spined stickleback, providing insights into host-parasite dynamics across different aquatic environments in the White Sea basin.

Schistosoma mansoni is a parasitic helminth that is vectored through freshwater snails. While the anti-schistosome defense of the South American snail, Biomphalaria glabrata, is well studied, little is known about the immune response of the African snail, Biomphalaria sudanica. We measured expression of five candidate immune genes in B. sudanica 8, 24, and 72 hours post-exposure to S. mansoni using reverse transcription quantitative PCR. Expression patterns of incompatible snails were compared to compatible snails and those sham exposed. We also assessed how diet (lettuce vs. pellet) affected expression of three genes, given prior findings that pellet-fed snails were more susceptible to S. mansoni. Results indicated that incompatible snails constitutively expressed higher levels of superoxide dismutase 1 (SOD1) than compatible snails at multiple time points, and of toll-like receptor (TLR) and granulin (GRN) at a single time point. Parasite-induced expression occurred at 8 hours in SOD1, biomphalysin 2, thioester protein 1 (TEP1), and granulin (GRN); however, for biomphalysin 2 and TEP1, induced expression was only detected for susceptible snails. At 24 hours, biomphalysin 2 expression increased in exposed resistant snails, and at 72 hours, all exposed snails decreased biomphalysin 2 expression compared to controls. Parasite-induced expression of SOD1, biomphalysin 2, TEP1, and GRN supports the hypothesis that these genes play a role in B. sudanica anti-schistosome defense; however, increased expression does not necessarily yield clearance of S. mansoni. SOD1 expression was higher in lettuce-fed snails at 8 and 24 hours, consistent with their greater resistance. Together, these results demonstrate the conserved and unique aspects of the B. sudanica anti-schistosome response.

Bone Morphogenetic Proteins (BMPs) are a highly conserved family of proteins involved in a variety of biological processes and developmental pathways critical for proper growth and the maintenance of normal physiological functions in animals. However, the specific BMP-like ligand in Fasciola gigantica, a zoonotic liver fluke of major veterinary and public health importance, has not yet been clearly identified and fully characterized. In this report, we describe the molecular structure, key characteristics, evolutionary relationships, and expression patterns of F. gigantica Decapentaplegic (FgDpp), a putative member of the BMP family. The complete cDNA sequence of FgDpp was 3,765 bp in length and included a 2,811 bp coding sequence (CDS), which encodes a 936-amino-acid precursor protein. This precursor is predicted to undergo proteolytic processing to yield a 185-amino-acid mature peptide. Sequence analysis revealed two conserved domains characteristic of BMP family members: a TGF-β pro-peptide domain and a TGF-β domain containing seven conserved cysteine residues. Expression profiling across developmental stages showed that FgDpp is highly expressed in embryonated eggs and metacercariae, with minimal expression in unembryonated eggs, newly excysted juveniles (NEJs), and adult flukes. These findings contribute to the molecular characterization of FgDpp and suggest its potential involvement in early developmental regulation, offering a foundation for future functional studies and potential targets for parasite control strategies.