The viruses associated with bats have generated significant concern; however, there is limited knowledge regarding the endoparasites that affect these mammals. This study involved the collection of seven nematode specimens (three males and four females) from the intestines of Hipposideros armiger in Shaoguan City, Guangdong, China. Next-generation sequencing was employed to obtain the mitochondrial DNA (mtDNA) genome, which was determined to be 14,130 base pairs in length. The mitochondrial genome comprised 12 protein-coding genes, 21 tRNA genes, 2 rRNA genes, and an AT-rich non-coding region. Phylogenetic analyses based on mtDNA sequences indicated that the nematode forms a sister clade to Nematodirus, exhibiting only 74% nucleotide identity. In contrast, the nuclear ITS1 gene demonstrated a high degree of nucleotide identity (98.6%–98.8%) with Durettenema guangdongense. Consequently, the parasitic nematode identified from H. armiger is likely to belong to the genus Durettenema and has been designated as Durettenema sp. 888. Furthermore, an epidemiological investigation revealed the presence of the parasitic nematode infections in H. armiger collected from Guangdong, Guangxi, and Guizhou Provinces. Given the widespread distribution of H. armiger and their tendency to inhabit areas in close proximity to human dwellings, the influence of parasite prevalence on bat population numbers and potential for human and domestic animal transmission of this pathogen warrants further investigation.

Stephanofilaria is a genus of nematodes that cause ulcerative dermal lesions in large mammals. However, there is a dearth of knowledge on the molecular genetics of Stephanofilaria species infecting critically endangered rhinoceros. This study employed genetic barcoding genes to identify Stephanofilaria species and to determine its genetic diversity and evolution. Phylogenetic analyses on partial genes of the second internal transcribed spacer Ribosomal DNA (ITS-2) and cytochrome c oxidase subunit 1 (Cox-1), revealed a 77% and 93% bootstrap support at the Cox-1 and ITS-2 loci respectively to a clade containing previously identified Stephanofilaria species. Morphological examination also confirmed features diagnostic of Stephanofilaria dinniki previously known to infect rhinoceros. Gene diversity of Cox-1 was 0.931 ± 0.030 and 0.579 ± 0.104 for the ITS-2, whereas nucleotide diversity was 0.008 ± 0.002 and 0.00197 ± 0.0016 for the Cox-1 and ITS-2 genes respectively. Neutrality tests (Fu and Li’s D* and Fu and Li’s F*) were significantly negative (p<0.05) at all loci, whereas Tajima D and Fu’s FS were each statistically significant (p<0.05) at the Cox-1 and ITS-2 loci respectively. The high gene diversity, low nucleotide diversity and negative neutrality tests are consistent with positive selection at the Cox-1 gene. Stephanofilaria infection among rhinoceros is currently restricted to highland sanctuaries compared to a widespread distribution in both lowlands and highlands in the 1960s suggesting an adaptation to vectors thriving in cooler highland temperatures. This is the first genetic identification of S. dinniki, in rhinoceros and will aid in diagnosis, treatment, studies, and rhinoceros conservation.

In this study, we investigated the diversity and survival of aestivating snails in dry-season rice paddies, focusing on their role as intermediate hosts for trematodes. A total of 1,159 snails from various families were collected and analysed, revealing nine species, primarily from the Bithyniidae family, with Bithynia siamensis siamensis being the most abundant. Of the nine species collected, the most common species, B. s. siamensis, exhibited a relatively high survival rate of 81.5% throughout the three-month dry period post-harvest, whereas the remaining eight species had survival rates below 24.0% (0–23.1%). Four snail species, B. s. siamensis, Filopaludina martensi martensi, F. sumatrensis polygramma, and F. doliaris, were found infected with larval trematodes, with an overall prevalence of 8.46% (57/674). The larval trematodes identified were categorized into four types: echinostome metacercaria, Thapariella anastomusa metacercaria, unidentified metacercaria, and unidentified rediae. These findings demonstrate that trematode infections can persist in aestivating snails despite the challenging conditions during the dry season, emphasizing the potential of aestivating snails to act as vectors for trematode transmission in agricultural settings. This underscores the need for effective management strategies to mitigate the risks associated with trematode transmission.

The techniques employed to collect and store trematodes vary between research groups, and although these differences are sometimes necessitated by distinctions in the hosts examined, they are more commonly an artefact of instruction. As a general rule, we tend to follow what we were taught rather than explore new techniques. A major reason for this is that there are few technique papers in the published literature. Inspired by a collaborative workshop at the Trematodes 2024 symposium, we outline our techniques and processes for collecting adult trematodes from fishes and discuss the improvements we have made over 40 years of dissections of 20,000+ individual marine fishes. We present these techniques for two reasons: first, to encourage unified methods across the globe, with an aim to produce optimally comparable specimens across temporal periods, across geographic localities, and between research groups; and second, as a resource for inexperienced researchers. We stress the importance of understanding differences in host biology and the expected trematode fauna, which ultimately enables organised and productive dissections. We outline our dissection method for each key organ separately, discuss handling, fixation, and storage methods to generate the most uniform and comparable samples, and explore ethical considerations, issues of accurate host identification, and the importance and potential of clear record keeping.

Steringotrema microacetabularis Suriano & Martorelli, 1983 (Fellodistomidae) was described from the flounder Paralichthys orbignyanus. Later, it was redescribed, based on new material from the same host and type locality, and reconsidered as Bacciger microacetabularis (Baccigeridae). The main difference noted in the redescription was the presence of spines on the body. However, the lack of DNA data made confirming the true affiliation of this digenean challenging. New specimens sampled from P. orbignyanus allowed us to sequence the 28S, ITS, and COI genes. Fresh specimens were stained to compare their morphology with the holotype and voucher specimens. The digeneans found correspond with those reported from Mar Chiquita, described as B. microacetabularis (=S. microacetabularis). Genetic analyses clustered the newly sequenced individuals within the Cryptogonimidae, showing relationships with Oligogonotylus manteri, Tabascotrema verai, and Caecincola parvulus (28S); T. verai, Lobosorchis spp., Euryakaina manilensis, and Metadena marina (ITS); and Siphoderina spp. (COI). After comparing the species with cryptogonimids lacking spines in the oral sucker, a new genus, Surianotrema n. gen., is described. This genus increases the number of cryptogonimid genera known in South America to seven – three in freshwater and four in marine environments – with Surianotrema n. gen. being the first to be sequenced. New sequences from other South American cryptogonimids are necessary to better understand the phylogenetic relationships between genera within this family, particularly in South America.

Gyrodactylidae Cobbold, 1864 is a monophyletic family of hyperviviparous species, with 36 genera and approximately 700 species. Here, we focused on one of these genera – namely Scleroductus Jara & Cone, 1989 – characterizing its morphological variation systematically and testing its phylogenetic position in relation to other genera in the family. We collected and describe two new species of monogenean parasites of Scleroductus infecting Neotropical freshwater catfishes in Mexico. Scleroductus veracruzano n. sp. infects Guatemalan chulín, Rhamdia guatemalensis in Veracruz, while Scleroductus oaxaqueno n. sp. infects filespine chulín, Rhamdia laticauda in Oaxaca, Mexico. Sequences of the internal transcribed spacer (ITS rDNA) and 18S rDNA were generated for both species. Phylogenetic hypotheses based on maximum likelihood and Bayesian inference analyses of 18S rDNA indicate that the two new Mexican taxa are closely related to each other, and both appear as sister species to an undescribed but molecularly characterized Scleroductus sp. infecting South American catfish, Rhamdia quelen in Brazil. Our analyses confirm the placement of Scleroductus spp. within the monophyletic family Gyrodactylidae, whose sister clade is the Oogyrodactylidae. Within Gyrodactylidae, Scleroductus spp. form a clade sister to a well-supported clade composed by members of the genera Ieredactylus, Gyrodactyloides and Laminiscus.

This report provides an overview of available data on the ultrathin structure and the mechanisms of formation of cysts around acanthocephalans of the classes Palaeacanthocephala and Archiacanthocephala in intermediate hosts. In most of the described cases, the cyst is bi-layered, consisting of an outer layer that is relatively thick and vesicular, and an underlying layer that is thin and amorphous. In acanthellae of some species, a lamellar layer is observed on the cyst surface, which degrades presumably at the cystacanth stage. Three probable mechanisms of cyst formation in acanthellae of different species have been identified. The first and second mechanisms involve the border of microvilli that develops on the tegument surface. In acanthellae of the first group, the cyst’s vesicular layer is formed by detachment of fragments or small vesicles from microvilli, a process resembling the micro-apocrine secretion, while the amorphous layer is composed of electron-dense material released from invaginates of the tegument’s outer membrane and the remaining microvilli. In acanthellae of the second group, the cyst is single-layered and formed presumably of whole microvilli separated from the tegument. Since acanthellae of the third group lack microvilli on the tegument surface, the vesicular layer of the cyst is formed of a few small vesicles and amorphous material synthesized deep in the tegument and in large vesicles transported to the parasite’s surface. The amorphous, electron-dense layer of the cyst is formed in the same manner as in the first group, but without microvilli.

The East Asian region has seen the first discovery of trematodes of the genus Psilotrema in the muskrat Ondatra zibethicus. When studying the morphology of the trematodes, two morphotypes were identified among individuals of Psilotrema spp., the differences between which at the morphological level are equivalent to those between species. The affiliation of one of these morphotypes with the bird parasite Psilotrema limosum was established based on partial sequences of genes coding for 28S ribosomal RNA, nad1, and cox1 mitochondrial DNA. Based on the analysis of these three markers, we classified individuals with this morphotype as P. limosum, despite some morphological features of worms infecting birds. At the same time, the worms with second morphotype had no interspecies differences based on the first two markers, while the cox1 gene confirmed the separation of these samples on a species level. These trematodes were described as a new species, Psilotrema elegans n. sp., based on both morphological and molecular data.

For many trematode species, individual reproductive parthenitae in first intermediate host colonies senesce, die, and are replaced by newly born parthenitae. The times involved in these processes are poorly understood. Here, we present an approach to estimate parthenita death rates and lifespans that uses readily obtainable data on senescent parthenita frequencies, brood sizes, and offspring (cercaria) release rates. The onset of parthenita senescence is often marked by the degeneration and disappearance of the germinal mass, its source of new offspring. Following germinal mass loss, the remaining viable offspring in a senescent parthenita finish development and are birthed before parthenita death. Therefore, a senescing parthenita’s remaining lifespan is the time it takes for all its viable offspring to mature and exit. We can estimate this time by measuring whole-colony (infected snail) cercaria shed rates, dissecting colonies to count reproductives, and then apply the per redia cercaria production rate to the observed brood sizes of senescent parthenitae. The per-capita parthenita death rate is then calculated as the proportion of parthenitae that are senescent divided by their average remaining lifespan. Reproductive parthenita lifespan is the inverse of this death rate. We demonstrate the approach using philophthalmid trematodes, first providing documentation of a free-floating germinal mass in 4 philophthalmids, and then, for 3 of those species, estimating parthenita senescence rates, death rates, and lifespans. This method should be broadly applicable among trematode species and help inform our understanding of trematode colony dynamics, social structure, and the evolution of parthenita senescence.

While most higher taxa in the Hemiuroidea exhibit remarkable diversity and thrive worldwide in marine ecosystems, a few groups have successfully radiated into freshwater environments. Among them, species of Thometrema are well known from freshwater and brackish fishes in the New World. In this study, specimens of Thometrema from a single specimen of the endangered pimelodid catfish Steindachneridion scriptum in the Upper Paraná River basin, State of São Paulo, Brazil, were subjected to morphological, ultrastructural (first scanning electron microscopy data for the genus) and molecular analyses. Newly obtained sequences of the partial large subunit nuclear ribosomal RNA (28S rDNA) and partial mitochondrial cytochrome c oxidase subunit I (COI mtDNA) provided strong evidence supporting the identification of the specimens as T. patagonicum, a trematode previously known only from endemic percichthyid fishes (Percichthyidae) in the Argentinian Patagonia. This unexpected finding, along with critical morphological evaluation of new and deposited material, led us to propose T. overstreeti and T. bonariense as junior synonyms of T. patagonicum. Moreover, we reassessed certain morphological features, revealed new potential distinguishing characters (papillae) and raised doubts about the taxonomic value of commonly used features for species differentiation (e.g., vitellarium masses). To overcome taxonomic problems in Thometrema due to the paucity of morphological features to clearly set species boundaries, new descriptions could leverage integrative approaches, as employed here, to establish robust species hypotheses and ultimately unravel the actual species composition in the Americas.

Trichinellosis is a global zoonotic disease affecting humans and nearly all animal species. The intestinal (enteric) phase of trichinellosis is critical, as it determines the course and prognosis of the disease. The medications used in the management of trichinellosis demonstrate inadequate bioavailability, along with a significant level of resistance. Therefore, there is a need for the development of novel agents that enhance the bioavailability of administered medications. Nanobiotechnology has emerged as a significant strategy in treating parasitic diseases. This study examined the use of solid lipid nanoparticles (SLNs) to improve the efficacy of oral ivermectin (IVM) in treating the enteric phase of trichinellosis. Thirty-five Swiss albino mice were divided into seven equal groups as follows: negative control, positive control, albendazole, ivermectin, SLNs, ivermectin loaded on solid lipid nanoparticles (IVM-SLNs), and a combination of IVM-SLNs and albendazole. Mice were sacrificed on the seventh day post-infection. The drugs’ effects were assessed using parasitological, biochemical, histological, histochemical and immunohistochemical analyses. The co-administration of albendazole and IVM-SLNs resulted in a significant decrease in adult burden, inflammatory cell infiltration, and apoptosis. Furthermore, a significant reduction in Cyclooxygenase-2 (COX-2) expression was observed compared to the infected untreated control group, along with improved liver and kidney function indices. In conclusion, the potent trichinocidal effect of a single oral dose of IVM-SLNs against Trichinella adults makes them a promising alternative or adjunct to existing nematicidal agents.

The description and delineation of trematode species is a major ongoing task. Across the field there has been, and currently still is, great variation in the standard of this work and in the sophistication of the proposal of taxonomic hypotheses. Although most species are relatively unambiguously distinct from their congeners, many are either morphologically very similar, including the major and rapidly growing component of cryptic species, or are highly variable morphologically despite little to no molecular variation for standard DNA markers. Here we review challenges in species delineation in the context provided to us by the historical literature, and the use of morphological, geographical, host, and molecular data. We observe that there are potential challenges associated with all these information sources. As a result, we encourage careful proposal of taxonomic hypotheses with consideration for underlying species concepts and frank acknowledgement of weaknesses or conflict in the data. It seems clear that there is no single source of data that provides a wholly reliable answer to our taxonomic challenges but that nuanced consideration of information from multiple sources (the ‘integrated approach’) provides the best possibility of developing hypotheses that will stand the test of time.

Benzimidazoles are the most frequently prescribed therapeutic options for treating trichinellosis in clinical settings; however, they have a lot of disadvantages. Therefore, researchers are focusing on the hunt for substitute chemicals. The goal of the current study was to compare the effectiveness of albendazole and the anti-diabetic medication metformin loaded on chitosan nanoparticles in treating mice infected with various stages of T. spiralis infection. 160 mice were included in the present study and divided into 8 groups: 6 experimentally treated groups, and positive and negative control groups. For studying the intestinal and parenteral phase, each group was broken into two more subgroups (a and b) according to the time of drug administration. The effects of albendazole, albendazole-loaded NPs, metformin, metformin-loaded NPs, combined albendazole and metformin, and metformin and albendazole-loaded NPs were assessed using parasitological studies, histopathological examination, and ultrastructural examination using SEM.

Statistically significant differences were detected in all studied subgroups compared to the control infected subgroup both in the intestinal and muscular phases. The greatest decrease in recovered adult worm and muscle larvae numbers was achieved by ABZ & MET/ Cs NPs. These findings were confirmed by histopathological examination. SEM examination of the tegument of T. spirals adult worms and muscle larvae showed destruction with multiple degenerative changes.

Our results suggested that metformin and its combination with albendazole especially when loaded on chitosan nanoparticles could be potential therapeutic alternative drugs against trichinellosis.

Parasite biodiversity is underestimated or unknown in many regions, yet information on parasites is critical to understanding ecosystem structure and how this will change into the future. Understanding the diversity and role of parasites is especially important in regions exposed to anthropogenic pressures, such as aquatic ecosystems, as their interactions with other stressors can either exacerbate or mediate negative impacts. Water scarcity in the Brazilian semi-arid has led to a proliferation of reservoirs for human use. These artificial waterbodies host a diversity of taxa, including a large number of fish species; however, fish parasite diversity remains undocumented. This study investigated the parasitological diversity of fishes from reservoirs in the Paraíba and Mamanguape River basins in the Caatinga domain, Brazil – one of the most populated semi-arid regions worldwide. Eight reservoirs were studied, with fish sampled across the two phases of the hydrological cycle (dry and rainy seasons) using gillnets, cast nets, and trawl nets. Endo- and ecto-parasites were identified and enumerated, and parasitological indices (prevalence, intensity, and abundance) were calculated. In total, 1,170 individuals of 21 fish species were examined. Of these individuals, 42% were parasitized with at least one of 54 parasite taxa. We recorded 32 new geographical occurrences of parasites and 23 new fish-parasite interactions, expanding our understanding of ichthyoparasite diversity in the Brazilian semi-arid. Moving forward, it is important to develop knowledge around how anthropogenic changes (e.g., biological invasions, climate, and land use change) influence host-parasite structure and dynamics and ecosystem functioning in these ecosystems.

Ochetosoma heterocoelium (Travassos, 1921) was collected from the mouth and oesophagus of a pit viper, Bothrops moojeni Hoge, 1966 in São Sebastião do Paraíso Farm (21°51’48.26" S, 48°26’56.78" W), municipality of Boa Esperança do Sul, São Paulo State, Brazil. In this study, we provide the first molecular characterisation of this digenean using 28S rDNA and COI sequences, and its phylogenetic position within the Plagiorchiida is assessed. Furthermore, new morphological features are added to the diagnosis of the species, and scanning electron microscopy photomicrographs are presented. Sequences of the 28S rRNA gene of O. heterocoelium were successfully obtained and aligned with 35 digenean species belonging to Plagiorchiida. Only three congeners – O. aniarum (Leidy, 1890), O elongatum (Seo et al. 2024), and O. kansense (Crow, 1913) – have been sequenced for this molecular marker. The newly sequenced individuals of O. heterocoelium are 98.7% and 99.4% similar to O. aniarum and O. kansensis, respectively, and Ochetosoma is not recovered as a monophyletic group. Dasymetra nicolli Holl and Allison, 1935 and Lechriorchis tygarti Talbot, 1933 are nested with Ochetosoma.

Two poorly known parasitic Platyhelminthes were collected from the gills of the European barracuda Sphyraena sphyraena in the western Mediterranean. Specimens of Chauhanea mediterranea Euzet & Trilles, 1960 and Rhinecotyle crepitacula Euzet & Trilles, 1960 (Polyopisthocotyla) are redescribed based on newly collected material. A careful examination of Ch. mediterranea revealed inaccuracies in previous interpretations of the female openings. The midventral opening, previously referred to as the ‘vaginal opening’ in Pseudochauhanea Yamaguti, 1965 and used to distinguish this genus from Chauhanea Ramalingam, 1953, is demonstrated to be the uterus, as confirmed by the presence of eggs in the thin-walled duct associated with this opening. The lateral position of the cirrus and vagina is also confirmed. Consequently, Pseudochauhanea is synonymized with Chauhanea, resulting in the following new combinations: Ch. elegans Fuentes-Zambrano, 1997 n. comb.; Ch. elongata Kritsky, Bilqees & Leiby, 1972 n. comb.; Ch. macrorchis Lin, Liu & Zhang in Zhang, Yang & Liu, 2001 n. comb.; Ch. mexicana Lamothe, 1967 n. comb.; Ch. sphyraenae Yamaguti, 1965 n. comb. A detailed investigation of the clamp sclerites of Ch. mediterranea indicates that both Chauhanea and Cotyloatlantica Bravo-Hollis, 1984 share the subdivision of the basal oblique sclerite, which is a continuation of the marginal sclerite in the anterior jaw, a key feature used to distinguish these genera. As a result, Cotyloatlantica is also synonymized with Chauhanea, and its species are transferred as follows: Ch. pretiosa (Bravo-Hollis, 1984) n. comb. The reinstatement of Ch. mediterranea Euzet & Trilles, 1960 as a valid name is supported, and an amended diagnosis of Chauhanea is provided. Additionally, R. crepitacula is accurately redescribed, with a new geographical locality record and an assessment of morphometrical and anatomical variations between Mediterranean and oceanic specimens.

In Japan, three trematode species of the genus Azygia have been recorded: A. gotoi, A. perryii, and A. rhinogobii. Here, we report the first detection of A. hwangtsiyui in Japan, identified from the introduced snakehead Channa argus. This trematode was previously known only from the snakeheads in mainland China. Between 2015 and 2024, we sampled snakeheads and snails in Japan, collecting adult trematodes and rediae. Adult trematodes were identified morphologically as A. hwangtsiyui, a determination corroborated by molecular analyses of the COI and 28S rDNA regions. Rediae extracted from the snail Sinotaia quadrata histrica were also identified molecularly as A. hwangtsiyui, indicating the snail acts as an intermediate host. Juvenile trematodes from the short-spined Japanese trident goby Tridentiger brevispinis were also morphologically identified as A. hwangtsiyui, indicating that this goby acts as a paratenic host. Given the snakehead’s introduction to Japan between 1923 and 1924, the absence of records of later introductions, and the presence of both intermediate and paratenic hosts in Japan at that time, A. hwangtsiyui was likely introduced concurrently with the snakehead. As the detection of three COI haplotypes suggests multiple introductions, subsequent introductions via the aquarium trade or other pathways involving the transport of freshwater fish and mollusks from Asia to Japan are also plausible.

The Neotropical region is considered a biodiversity hotspot for reptiles, with eight families of terrestrial and freshwater chelonians. Parasites are of great importance to aquatic ecosystems and are essential to host communities. They help understand the patterns and phylogenetic relationships of their hosts and act to control populations. A literature survey on helminth parasites of chelonians in the Neotropical region was conducted, examining the most commonly found groups of helminths, the most parasitized hosts, compiling their biogeographical and political distribution and recording the parasite fauna of Phrynops geoffroanus in the state of Paraíba, northeastern Brazil. Considering the literature from 1850 to 2024, 202 helminth taxa were recorded. The Mesoamerican dominion had the highest number of helminth taxa, and Brazil was the political unit that recorded the most helminth taxa, followed by Mexico. Nematoda was the group with the highest number of taxa and occurred in all biogeographical units, with the species Spiroxys contortus being the most commonly found, followed by Trematoda, represented by the most commonly found species, Nematophila grandis. Hosts from the Chelidae family had the highest number of helminth taxa, followed by the Kinosternidae family. The most parasitized host species were Chelonoidis denticulatus and Phrynops hilarii. For the host Phrynops geoffroanus, the first occurrence of the nematode helminth Spiroxys contortus was recorded. This is the first study to include all parasitic helminths of terrestrial and freshwater chelonians in the Neotropical region, including a new occurrence in a chelonian host in the hinterland of Paraíba, Brazil.

Accacoeliid digeneans associated with fish of the family Molidae exhibit enigmatically high taxonomic diversity. However, the phylogenetic relationships between species within this digenean taxon are poorly understood. In the present study, the first nuclear 28S rRNA gene, ITS2 region of nuclear DNA, and mitochondrial cox1 gene sequence datasets were obtained for two members of the Accacoeliidae, a type and only species of the genus Odhnerium Yamaguti 1934 and an unidentified Accacladocoelium sp. collected from Mola mola (Linnaeus, 1758) off Iturup Island. Analyses of molecular differentiation and phylogenetic relationships indicate that Accacladocoelium sp. is a sister species to Accacladocoelium nigroflavum (Rudolphi, 1819). The genus Odhnerium is closely related to Tetrochetus Looss, 1912, on the 28S rRNA gene-based phylogenetic tree. Results of phylogenetic analysis based on both the mitochondrial cox1 gene and the concatenated ribosomal ITS2 region and cox1 gene of mtDNA show that the genus Odhnerium is close to the A. nigroflavum + Accacladocoelium sp. clade. In turn, the genus Accacladocoelium does not have monophyletic status in the trees reconstructed from these data.