Schistocephalus spp. are widely distributed Holarctic cestodes that comprise key model species for host-parasite studies. S. solidus and S. pungitii, the most extensively studied species, exhibit narrow host specificity. Another species, S. cotti, is known from the European bullhead (Cottus gobio); however, information on its host range, geographical distribution, and molecular data remain poorly characterized. In Siberia, plerocercoids of Schistocephalus found in sculpins were previously recorded from endemic cottid fishes of Lake Baikal and were identified as S. solidus, which is inconsistent with the known host specificity of this species. The present study aims to clarify the species identity of Schistocephalus from Siberian cottid fishes using morphological and molecular data, and to test the hypothesis of conspecificity of Schistocephalus plerocercoids from sculpin hosts across Eurasia and North America. Morphologically, Siberian plerocercoids correspond to the description of S. cotti, supporting their assignment to this species. The phylogenetic analysis confirmed the identity of the plerocercoids as S. cotti and demonstrated the existence of two distinct Schistocephalus lineages in North America and Siberia. These findings indicate that at least two different Schistocephalus species infect sculpins in the Old and New Worlds.

Specimens of the Nile puffer, Tetraodon lineatus Linnaeus (Tetraodontiformes: Tetraodontidae), were collected from the Nile River, Qena Governorate, Egypt (26°08′N, 32°42′E), and examined for monogenoidean parasites. A single species, initially identified as Heterobothrium lineatum Morsy, Saady, Abdel-Gaffar, Bashtar, Melhorn, Al Quraishy & Adel, 2012 (Monogenoidea: Diclidophoridae), was recovered from the gill lamellae of six out of seven examined hosts (prevalence = 86%). The taxonomic and phylogenetic status of this helminth was reassessed using an integrative approach combining morphological and molecular data. Comparative morphological analysis revealed that H. lineatum represented a junior subjective synonym of H. fluviatile Euzet & Birgi, 1975. Molecular analysis based on the 28S rDNA gene, representing the first inclusion of H. fluviatile as an ingroup taxon, placed this species within a well-supported clade of Heterobothrium species infecting tetraodontid fishes. Heterobothrium indicum Verma, 2022, a parasite of the goldband goatfish, Upeneus moluccensis (Bleeker) (Mulliformes: Mullidae), is herein transferred to Upenicola Unnithan, 1966 as Upenicola indicus (Verma, 2022) n. comb. The study highlighted the need for further investigation into the taxonomic status of Diclidophora indica Tripathi, 1959, and Neodiclidophora simhai Gupta & Krishna, 1980, as probable members of Heterobothrium. Moreover, Heterobothrium lamothei of Morsy et al. (nec Vidal Martinez & Mendoza-Franco) is regarded as a species inquirenda.

We recorded Gyrodactylus teuchis Lautraite, Blanc, Thiery, Daniel & Vigneulle, 1999 on one-year-old farmed rainbow trout Oncorhynchus mykiss (Salmoniformes, Salmonidae) from Lake Kalmozero (White Sea drainage system, Republic of Karelia, Russia) in May and October 2023. Morphological identification of these specimens was confirmed by molecular data on the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene and the ribosomal internal transcribed spacer 2 (ITS2). Analyses of the newly obtained cox1 gene sequences show they are identical to fragments of sequences of this gene for G. teuchis individuals collected from wild S. trutta in Slovenia and from farmed S. trutta in Russia. Sequencing of the ITS2 region revealed ribotype D found previously in wild S. trutta and S. fontinalis in Austria, and in farmed S. trutta and O. mykiss in Poland. The infection prevalences in the caged rainbow trout were 100% and 75%, and the mean abundances were 20.8 and 18.1 ind., in May and October, respectively. There were no significant differences between the parasite abundance distributions in these two months, likely indicating similar levels of resistance to the infection. This is the first report on G. teuchis from the White Sea drainage basin as well as in farmed rainbow trout in Russia. This new finding is a signal for veterinary authorities to strengthen parasitological monitoring of transported stocking material.

In this report, morphological and molecular characteristics are provided for two members of the subfamily Microphalloidea distributed in the south of the Russian Far East. Some of trematode specimens found in larvae of mayflies, stoneflies, and caddisflies and then experimentally reared to the adult stage in hamsters, according to their morphological features, belong to the species Acanthatrium ovatum previously recorded from Japanese bats. Molecular data has confirmed their membership in the family Lecithodendriidae and similarity to trematodes identified as Lecithodendriidae sp. F from Japan. The other specimens, experimentally reared in chickens, according to their morphological characteristics, meet the diagnostic criteria of the genus Parabascus. However, this species is not clustered with representatives of this taxon in the phylogenetic reconstruction based on 28S rRNA gene data. A molecular analysis has shown that it forms a single cluster with Pachypsolus irroratus and is a member of the family Pachypsolidae. It is here placed in the new genus Pseudoparabascus n. g. under the name Pseudoparabascus khotenovskii comb. n. The phylogenetic reconstructions based on two other markers, the cox1 mtDNA gene and the ITS2 rDNA region, have confirmed the assignment of these specimens obtained in both experiments to the above-considered taxonomic groups.

Hosts function as ecological islands for endoparasites, offering structured habitats that support parasite survival, growth, and reproduction. Larger and older hosts are often expected to harbour more diverse and abundant parasitic assemblages due to increased structural complexity and longer exposure times. In this study, we investigated how host body size and phylogenetic relatedness influence endoparasite mean richness and mean intensity of infection in lizards from the Atlantic Rainforest of northeastern Brazil. We analysed 121 parasitised specimens representing 15 species, recording body size metrics (SVL and mass) and calculating parasitological indices. Significant phylogenetic signal was detected for host body size (SVL and mass) and mean intensity of infection, whereas no phylogenetic signal was found for mean parasite richness. Contrary to the island theory predictions, PGLS models revealed a significant negative relationship between mean SVL/mass and mean intensity of infection. Furthermore, no significant relationship was found between host body size (SVL or mass) and mean parasite richness, regardless of the evolutionary model used. The pPCA identified a predominance of global structure (phylogenetic relatedness), explaining 42.15% of the variation, while local structures, reflecting niche differentiation, accounted for 18.61%. Our results demonstrate that lizard–parasite interactions are shaped by a complex synergy between conserved evolutionary templates and opportunistic ecological responses, highlighting the necessity of integrated phylogenetic approaches in parasitological studies.

Posthodiplostomum minimum (MacCallum, 1921) Dubois, 1936 (Digenea, Diplostomidae) was described from adult worms from a great blue heron (Ardea herodias; Ardeidae) in New York. Metacercariae have been widely reported from diverse freshwater fishes, despite early experimental work and recent molecular data indicating exclusive infection of minnows (Leuciscidae) in North America. We compared the type specimens of P. minimum to adults taken from domestic chicks (Gallus gallus domesticus) fed metacercariae from fathead minnow (Pimephales promelas; Leuciscidae), as well as adults in naturally infected ardeid hosts. Sequences of cytochrome c oxidase I (CO1) showed these specimens were conspecific with worms from leuciscids and ardeids sampled across North America. However, adult morphology of the species with metacercariae in North American leuciscids differed markedly from the type specimens of P. minimum. Consequently, we resurrect and transfer to Posthodiplostomum Dubois, 1936, the earliest name for the lineage infecting leuciscids in North America: Posthodiplostomum vancleavei (Agersborg, 1926) n. comb. In North America, the four most likely junior synonyms of P. minimum are Posthodiplostomum aztlanensis González-García, López-Jiménez, Ortega-Olivares, Sereno-Uribe, Pérez-Ponce de León et García-Varela, 2024, Posthodiplostomum dawnsherryae Achatz, Von Holten, Pritchard et Keel, 2025, Posthodiplostomum nanum Dubois, 1937, and Posthodiplostomum seminolense Achatz, Von Holten, Pritchard et Keel, 2025. Sequences of CO1 indicate P. vancleavei n. comb. has been introduced in Japan and we discuss the high likelihood of its establishment in Europe. The complete rDNA operon and near-complete mitochondrial genome sequence of P. vancleavei show expected phylogenetic affiliation with Posthodiplostomum centrarchi Hoffman, 1958.

Between 2019 and 2025, metacercariae of the trematode genus Lecithocladium (Hemiuridae) were found in gelatinous zooplankters occurring in Japanese coastal waters. To identify these metacercariae and elucidate their life cycles, fish hosts were simultaneously examined for adult trematodes. Molecular analyses of the nuclear 28S ribosomal RNA (rRNA) and mitochondrial cytochrome c oxidase subunit 1 (COI) regions, comparing them with adult Lecithocladium species from fish hosts, confirmed the metacercariae as those of L. magnacetabulum and L. cf. excisiforme. Metacercariae of L. magnacetabulum were detected in the comb jelly Beroe cucumis and the jellyfish Aequorea coerulescens; adults of this species had previously been recorded in the Japanese butterfish Psenopsis anomala and the red seabream Pagrus major. For L. cf. excisiforme, metacercariae were detected in the arrow worm Aidanosagitta crassa and an adult in the whitetongue jack Uraspis helvola. These predatory gelatinous zooplankters are presumed to be the third (or higher) intermediate or paratenic hosts, given that their prey, planktonic copepods, are typically reported as the second intermediate hosts for hemiurid species. Furthermore, adults of two additional hemiurid species, L. excisum and Ectenurus trachuri, were also isolated from the fish hosts. Cumulatively, this work and previous research suggest that gelatinous zooplankters represent crucial transmission routes for hemiurid trematodes.

Percutaneous treatments (PTs) are established minimally invasive options for the management of hepatic cystic echinococcosis (HCE). Conventional techniques include puncture, aspiration, injection, and re-aspiration (PAIR), which relies on scolicidal agents, and puncture, aspiration, injection, and drainage (PAID), which uses prolonged catheter drainage to evacuate cyst contents. In this study, we describe our experience with a modified PAIR technique for the treatment of hepatic cystic echinococcosis. Eight patients with 19 cysts were initially included, and outcomes were analyzed in 6 patients with 9 cysts who had complete follow-up imaging.

Under CT guidance, a transhepatic puncture of the cyst was performed. Partial aspiration was followed by injection of hypertonic saline. After cystography, an 8-French catheter was introduced to replace the 18-gauge needle, allowing controlled aspiration. The injection and aspiration sequence was repeated three to four times. The catheter was removed early after complete cyst content evacuation. In cysts larger than 10 cm, 95% ethanol was used as the scolicidal agent.

Follow-up imaging showed a significant reduction in cyst volume. Outcomes achieved with this modified PAIR technique were compared with previously reported percutaneous HCE treatment series in the literature and appeared to fall within the range of outcomes reported in prior percutaneous series. Notably, this technique enabled successful treatment of a complicated cyst associated with a gastric fistula in a single patient.

Percutaneous management of HCE continues to evolve, and modified techniques allow tailored treatment based on cyst characteristics. Our modified PAIR approach proved effective for both simple and multivesicular cysts and demonstrated technical feasibility in a single complicated case with gastric fistula.

Proterodiplostominae Dubois, 1936 is a small but evolutionarily significant lineage of diplostomid trematodes that primarily parasitize crocodilians, with fishes acting as second intermediate or paratenic hosts. In Peru, knowledge of this group has been limited to the record of adult specimens of Proterodiplostomum longum (Brandes, 1888) recovered from Caiman crocodilus Linnaeus, 1758 (Sauropsida: Alligatoridae) in the Loreto region, and molecular evidence linking larval and adult stages has been absent. The present study provides the first integrative morphological and molecular characterization of Proterodiplostominae metacercariae infecting siluriform fishes in the Peruvian Amazon Basin. Metacercariae were collected from Hoplosternum littorale (Hancock, 1828) (Callichthyidae) and Pterygoplichthys pardalis (Castelnau, 1855) (Loricariidae) and examined using light and scanning electron microscopy, together with partial 28S rDNA and mitochondrial cox1 sequences. Phylogenetic analyses of 28S rDNA demonstrated that three isolates clustered within a strongly supported clade containing reference sequences of P. longum from crocodilian hosts, with minimal genetic divergence (≤0.536%), confirming their conspecificity. This study therefore provides the first molecularly supported record of P. longum metacercariae in Peruvian fishes and clarifies a previously undocumented component of its life cycle. In addition, phylogenetic analyses revealed two distinct evolutionary lineages (designated herein as Proterodiplostominae gen. sp. 4 and gen. sp. 5) exhibiting 9.882% mitochondrial divergence, suggesting previously unrecognized diversity within the subfamily. These findings expand the known host range of P. longum, provide new genetic data for larval stages of Proterodiplostominae in the Neotropics, and highlight the importance of integrative approaches for resolving life-cycle stages and species boundaries in Diplostomidae.

Here we report microfossil helminth analysis of 18 soil/sediment samples from the Letchworth site, Florida, dating c. 400 BC–AD 800 in the Woodland Period. The discovery of helminth eggs of Toxocara canis, Dipylidium caninum, a species of taeniid cestode, and Hymenolepis sp. provides probable evidence of domesticated dogs, and possibly also commensal rodents that could have been hunted or attracted to settlement. The parasites could have affected the health of people and their dogs. Helminths provide crucial faunal evidence at the site, as there is a lack of macro-remains due to poor preservation. The relatively high frequency of T. canis eggs at Letchworth (11 samples) is consistent with that at the Cloudman site in Michigan (another North American site where T. canis helminths have been identified), where all samples analysed (12) contained these eggs, while the other helminth types were recorded in fewer samples. This consistency could reflect extensive, intensive human-dog associations for long periods in North America, in conjunction with direct faunal evidence for dogs and other parasitological evidence indicating T. canis. The Letchworth results offer a new line of probable evidence of domesticated dogs in the American Southeast, particularly along the Gulf Coast where bone material is often poorly preserved.

During a helminthological survey conducted in the Peruvian Amazon, nematodes representing an undescribed species of Denticamallanus Moravec and Thatcher, 1997 (Camallanidae: Procamallaninae) were recovered from the intestine of Centromochlus heckelii (De Filippi, 1853) (Siluriformes: Auchenipteridae). The new species, Denticamallanus peruensis n. sp., is described herein based on an integrative taxonomic approach combining detailed morphological analysis using light and scanning electron microscopy with molecular characterization of the partial 18S rDNA gene. Denticamallanus peruensis n. sp. is distinguished from its congeners by the morphology of the male caudal extremity, which forms broad lateral lobes giving a spade-like appearance, the arrangement of caudal papillae (one pair of preanal and four pairs of postanal papillae), and spicule length (50–100 μm). Phylogenetic analyses based on Bayesian inference methods recovered the new species within a well-supported clade of Spirocamallanus spp., whereas other species currently assigned to Denticamallanus formed a separate lineage, indicating possible non-monophyly of the genus. This study represents the first description of a Denticamallanus species from C. heckelii in the Peruvian Amazon and increases the number of recognized species within the genus. In addition, these findings challenge the expanded generic diagnosis recently proposed for Denticamallanus and reinforce growing evidence that buccal capsule morphology alone may not reliably reflect evolutionary relationships within Camallanidae.

Elephants harbour intestinal nematode infections, particularly cyathostomine nematodes (Cyathostomini: Strongylidae). Monitoring helminths in rare and endemic species is crucial, as infections can contribute to population declines. The Sumatran elephant (Elephas maximus sumatranus), a subspecies of the Asian elephant, is native exclusively to the island of Sumatra, Indonesia. The studies on nematodes of Sumatran elephants remain limited. In this study, three cyathostomine nematodes not previously reported from Indonesia – Quilonia renniei, Murshidia (Murshidia) falcifera, and M. (M.) murshida – were redescribed using light microscopy and scanning electron microscopy. This approach enabled the observation of previously unreported morphological features of taxonomic significance and corrected existing errors. Our SEM observations showed for the first time the detailed morphology of the cephalic extremity and the bursa of Murshidia (M.) falcifera, and M. (M.) murshida. Additionally, we provide the first molecular data on the nuclear DNA region (ITS1, 5.8S, and ITS2) of Q. renniei, the first mitochondrial partial cytochrome c oxidase I (COI) sequences for M. (M.) murshida and M. (M.) falcifera, and newly generated COI data for Q. renniei. These sequences were used to construct a phylogenetic tree of the elephant nematodes belonging to the Tribe Cyathostomini. The ITS phylogeny supported the monophyly of Murshidia and Quilonia and placed Khalilia sameera as a basal lineage, whereas the COI dataset failed to resolve relationships at the generic level. The ITS tree also confirmed the identity of Q. renniei, which appeared as sister to Q. africana.

A new species of Calicotyle (Monogenea: Monocotylidae) is described from three deepwater catshark species (Elasmobranchii: Pentanchidae) collected off Iceland. Calicotyle carmenae n. sp. is diagnosed as a species of Calicotyle possessing a haptor with one central and seven peripheral loculi, two hamuli, and several hooklets. It is distinguished from all congeners by the absence of eye spots, having a once-looped male copulatory organ, two U-shaped vaginae, and intercaecal vaginal pores. A molecular phylogenetic analysis based on 28S ribosomal DNA sequences placed Calicotyle carmenae n. sp. within a clade of other Calicotyle species infecting selachians and holocephalans, while revealing clear genetic divergence from these congeners (8.2–11.1%; 74–99 bp). In addition, the morphology and host specificity of C. carmenae and its congeners are discussed. Some inconsistencies and insufficiently described anatomical features in other species of the subfamily Calicotylinae are highlighted, which evidence a need for a revision of this taxon. The study also provides the first record of a species of Calicotyle from pentanchid sharks, highlighting the potential for further discoveries as research expands into different hosts and deeper, underexplored marine ecosystems.

Migratory hosts are key vectors of long-distance parasite dispersal. In the North Atlantic, migratory connectivity of avian hosts suggests that diplostomid trematodes with broad host specificity could potentially exhibit widespread distributions. However, host migration does not necessarily result in successful parasite dispersal. We investigated the diversity and distribution of Diplostomum spp. infecting freshwater salmonids in Greenland and the Faroe Islands using a metabarcoding approach. In Greenland, infection prevalence in Arctic char and Atlantic salmon ranged from 0% to 100% across locations. Molecular analysis revealed four lineages, including the first records of Diplostomum sp. 6, 7, and 9 (Locke et al. 2010a; 2010b), and a novel lineage/species showing 92.6–94.2% sequence identity to its closest relatives. In contrast, no evidence of diplostomid infection was found in brown trout and Atlantic salmon collected from sixteen streams in the Faroe Islands. The presence of a novel, locally abundant (28.9% prevalence) parasite lineage/species in Greenland, the affinity of these parasite assemblages with those in North America, the lack of overlap with Icelandic and Norwegian communities, and the absence of diplostomids in Faroese salmonids indicate limited bird-mediated dispersal of diplostomids across the North Atlantic. We propose that a ‘short transmission window’ at high latitudes during the breeding season, combined with specific avian migration routes, may limit long-distance dispersal and promote regional isolation between Nearctic and Palearctic diplostomid communities across the North Atlantic.

Pelagic gastropods, including holoplanktonic and neustonic species, have been considered potential sources of trematodes that parasitize marine fishes. However, the taxonomy and life cycles of metacercariae detected in pelagic gastropods remain poorly understood. This study examined metacercaria infections in 10 species of pelagic gastropods (N = 415) collected from Japanese coastal waters between 2016 and 2025. Metacercariae were detected in four pelagic gastropod species and were identified as seven trematode species based on molecular analyses of the 28S ribosomal RNA and cytochrome c oxidase subunit 1 regions. In holoplanktonic gastropods, six species within the family Lepocreadiidae were molecularly identified as Cephalolepidapedon saba, Prodistomum orientale, Prodistomum sp., Opechona sp., Preptetos sp., and Lepocreadiidae gen. sp., all of which represent new host-parasite records. A metacercaria molecularly identified as Dinurus tornatus (Hemiuridae) was detected in the neustonic gastropod Glaucus atlanticus. These results confirm that pelagic gastropods can act as the second intermediate or paratenic hosts and suggest predator–prey relationships with marine fishes. In addition, rediae obtained from benthic gastropods (cowries) were examined molecularly and identified as Prodistomum sp., thereby clarifying aspects of its life cycle.

A new species of thrips-parasitic nematode, Thripinema usitatum n. sp. (Tylenchomorpha: Allantonematinae), is described from thrips collected from flowers in Hainan Province, China. The species is identified using an integrative approach combining detailed morphology, molecular phylogenetic analyses, and biological observations. Thripinema usitatum n. sp. exhibits pronounced sexual dimorphism and a complex life cycle, including obese parasitic females, vermiform infective females, and free-living males with degenerate feeding structures within the body of thrips. The new species is distinguished from its congeners by the absence of a stylet in free-living males, a distinctive two-part bursa extending nearly to the tail terminus, and characteristic shapes of parasitic females and male tails. Molecular characterization was performed using three markers (18S rRNA, 28S D2–D3 rRNA, and mitochondrial cytochrome c oxidase subunit I, mtCOI). Phylogenetic analyses based on 28S D2–D3 rRNA and mtCOI partial sequences consistently recovered T. usitatum n. sp. as a well-supported, monophyletic lineage clearly separated from other entomophilic nematodes. Among the markers examined, mtCOI provided the highest discriminatory power. Biological observations revealed that T. usitatum n. sp. infects thrips at all developmental stages, with a strong prevalence in adult females. Multiple nematode life stages frequently co-occurred within individual hosts, and infection intensities ranged from 1 to 433 nematodes per thrips. These results expand the known diversity of Thripinema and provide a robust framework for future systematic and ecological studies of thrips-parasitic nematodes.