Five species of monorchiids are known from fishes of the family Gerreidae, of which one is from Australian waters. Here, we report it and two new monorchiids from three species of Gerres Quoy & Gaimard, 1824 from off Lizard Island, northern Great Barrier Reef, and Moreton Bay in south-eastern Queensland: Gerres oyena (Forsskål), Gerres oblongus Cuvier and Gerres subfasciatus Cuvier. One of the new species, found only in G. oblongus at Lizard Island, conforms most closely to the concept of Proctotrema Odhner, 1911. However, it differs from species of Proctotrema in oral sucker shape and location of intestinal bifurcation and termination. It is phylogenetically distinct from two sequenced species of Proctotrema; thus, we propose Obscuromonorchis ranae n. g., n. sp. The second new species infects all three gerreids, occurs at both Lizard Island and Moreton Bay, and is morphologically most similar to the concept of Monorchicestrahelmins Yamaguti, 1971. However, the combination of the length of the caeca, size of the testis and post-testicular region, and the form of spination in the genital atrium presents a clear genus-level distinction that warrants proposal of a new genus. There are no molecular data for the three recognised species of Monorchicestrahelmins. We propose Argenticola shuyinae n. g., n. sp. for this species. New specimens of Gerricola queenslandensis Wee, Cutmore & Cribb, 2021 were collected from off Lizard Island and Moreton Bay. The three species form a well-supported clade but with internal branch lengths and topology consistent with genus-level differentiation.

A new species of Loimos MacCallum, 1917 is described more than half a century after the last species was described in 1972. The new species was collected from the gills of Rhizoprionodon taylori (Ogilby, 1915) off the Central Queensland coast, Australia, and is the first Loimos species and the first representative of the Loimoinae Price, 1936 known from Oceania. A detailed morphological description and 28S rDNA molecular sequences are provided for the new species. In the molecular phylogeny based on available 28S rDNA sequences for relevant Monocotylidae, the new species grouped together with the only other Loimos sequence available in GenBank, that of the nonugen Loimos sp. from China (OM060238), sister to Loimosina wilsoni Manter, 1944. The estimated genetic divergence between the new species and the nonugen Loimos sp. sequence is low, between 0.0452 and 0.0737, suggesting that the nonugen sequence may represent the new species, or a very closely related congener. Host identity was confirmed by comparing COI sequences with those of known sharks in GenBank. We also provide the first 12S and 16S molecular sequences for this shark species.

Data on the infection of Middendorffʼs eelpout, Hadropareia middendorffii, by metacercariae of the trematodes Cryptocotyle lingua Creplin, 1825 and Liliatrema skrjabini Gubanov, 1953, which are causative agents of black spot disease, is provided here for the first time for Taui Bay, Sea of Okhotsk. The prevalence of infection of fish by larvae of C. lingua reached 79%, while the intensity of infection varied from one to 278 individuals (with an average of 53). The prevalence of infection by L. skrjabini was lower (40%), with an intensity from one to 22 larvae (on average, eight). Metacercariae of both trematode species were surrounded by two envelopes: an outer, connective tissue capsule formed by the host’s cells, and an inner cyst formed by the parasite. The examined metacercariae were found in all regions of the fish’s body (head, trunk, and fins), with approximately equal numbers of individuals of both species found in tissues of the head and trunk regions. Metacercariae of C. lingua were localised in the fishes’ muscles, not only immediately under the skin but also in deeper layers. The capsules formed around metacercariae of both trematode species were dominated by fibroblasts and collagen fibres and did not show pronounced signs of inflammation. Studying the distribution of black spot disease and its effects on fish is crucial for understanding disease patterns in relation to fish population dynamics. It may also inform the development of effective anthelmintic treatments for use in aquaculture farms.

Trichinellosis is a parasitic zoonosis caused by a nematode parasite of the Trichinella (T.) genus. It poses significant public health issues due to limited effective and safe treatment options, especially for the muscle-encysted larval stage. Citrus paradisi (C. paradisi), with its high content of flavonoids and polyphenols, has been recorded to possess anti-parasitic properties and numerous therapeutic applications. The present work aimed to assess the efficacy of C. paradisi extract peel extract as a therapeutic agent, either alone or combined with albendazole (ABZ), against T. spiralis in experimentally infected mice. Sixty-six lab-bred Swiss albino mice were divided into control and treatment groups, then received either ABZ, C. paradisi extract, or a combination of both during the enteral, migratory, and encapsulation phases of infection. Parasitological, histopathological, and immunohistochemical examinations were performed to evaluate the efficacy of the treatments. All treated groups displayed a highly significant difference (p < 0.001) in larval counts compared to the positive control group, with the combination therapy group having the highest efficacy and the lowest mean count value during different treatment regimens. In addition, treated groups showed improved muscle integrity compared to the positive control group. Moreover, the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) showed the highest expression reduction in the combination therapy group. These findings highlight the potential of C. paradisi as a complementary therapy to albendazole for treating trichinellosis through muscle larva reduction and mitigation of inflammation.

Cystic echinococcosis is a zoonosis caused by Echinococcus granulosus sensu lato, which leads to serious public health problems. Considerable phenotypic variation has been described between parasites depending on the intermediate host and genotype. Knowledge of species/genotypes present in an endemic region is clue for control programs. Although DNA sequencing is the most accurate tool for this purpose, its high cost makes it less affordable. A multivariate study of the morphometric parameters of rostellar hooks of E. granulosus sensu lato of human origin from Neuquén was carried out using Principal Components Analysis and classification trees. A valid classification criterion to differentiate E. granulosus species using morphometry of rostellar hooks in human hydatid cysts was determined. Seventy-six human fertile hydatid cysts (48 E. granulosus sensu stricto G1 and G3, and 28 E. canadensis G6) were included. Overall, 2,280 hooks were measured. The rostellar hooks belonging to E. granulosus sensu stricto were significantly smaller than those of E. canadensis. The Large Total Length (LTL) was sufficient to classify a new isolate into the 2 species: if LTL < 25.3 μm, then it corresponds to E. granulosus sensu stricto, and if LTL ≥ 25.3 μm to E. canadensis. This is the first multivariate study that establishes a morphometric cut-off value to discriminate between 2 species of E. granulosus sensu lato from human patients, using a significant number of cysts of both species identified by sequencing of mitochondrial genes. It constitutes a useful predictive tool in endemic areas where both human infective species overlap.

Genetic evidence indicates that Progamotaenia macropodis Beveridge, 1976 (Cestoda: Anoplocephalidae), found in various macropodid host species, is a complex of cryptic species. However, the genetic data are incomplete, and no morphological re-appraisal of the species has been undertaken since its original description. Here, additional mitochondrial cytochrome c oxidase I sequence data have been added from the type host, Macropus giganteus, as well as other host species, and a morphological study of all available material undertaken. A new species, Progamotaenia mollicula sp. nov., is erected for specimens from the tammar wallaby, Notamacropus eugenii, which are smaller, and the testes in pre-mature and mature proglottids occur invariably in two lateral groups. Specimens from the remaining host species, Macropus fuliginosus, Notamacropus parryi, N. rufogriseus, Osphranter robustus, and Wallabia bicolor are highly variable with obvious differences in length and proglottid shape, but with no reliable internal morphological characters for separating the various genotypes. The study was limited by incomplete molecular data (N. rufogriseus) and the poor quality of some of the preserved material.

Haemonchosis is a fatal disease of livestock caused by Haemonchus contortus (HC) – a blood-sucking parasite of the abomasum. This parasite is quite prevalent in sheep, causing mortality and production losses. The suppressor of cytokine signalling-2 (SOCS2) gene plays a vital role in sheep’s immune response against gastrointestinal parasites. This study aimed to estimate the parasitic load of HC in three sheep breeds (Balkhi, Ghalji, and Michni) through faecal egg count and to identify SNPs in the SOCS2 gene associated with the susceptibility of sheep against HC. The results showed that the mean number of HC eggs per gram (EPG) was higher in the faecal samples of Ghalji (4022 ± 1162 EPG), followed by Michni (1988 ± 367 EPG), while the HC EPG was the lowest in Balkhi sheep (1535 ± 552 eggs/gm). Sequencing results showed polymorphisms in the SOCS2 gene between the low-infection and high-infection categories of the three sheep breeds. A total number of six genic variants were observed, of which three were SNPs, one was insertion, and two were deletions. Polymorphisms were observed in the intronic and 3′ UTR regions of the SOCS2 gene. A deletion (c.1083delGCA) in intron 1 and an insertion (c.3304insT) in intron 2 showed positive correlations (0.833 and 0.889, respectively) with the HC infection, while one SNP in the 3′ UTR region showed negative correlation (–0.654). This study provides a basis for selecting resistant sheep against HC infection based on the SOCS2 gene molecular markers.

The cestode Gerbillitaenia psammomi (Cyclophyllidea: Catenotaeniidae: Skrjabinotaeniinae) was found parasitizing fat sand rats (Psammomys obesus) in the south of Tunisia. The species was found previously in P. obesus from Egypt and in Meriones shawi from Morocco. The present finding constitutes the first record of the species in Tunisia. In the present study, G. psammomi was morphologically characterized using light microscopy and compared to previous records of the species. The main differentiating morphological features of G. psammomi with respect to other skrjabinotaenines of North African Gerbillinae murids are, in particular, the shape of strobila, size of suckers, number of testes, absence of an antero-poral ovarian lobe, length of the central uterine stem, and number of primary uterine branches. Negative density-dependent growth (crowding effect) has also been reported. Molecular analysis based on 28S rDNA was performed for G. psammomi and for Skrjabinotaenia oranensis. Thus, both species are grouped in a clade with other species of the subfamily Skrjabinotaeniinae and are clearly separated from the clade that includes species of the subfamily Catenotaeniinae. The molecular study confirmed the previously postulated synonymy of Meggittina numida with S. oranensis.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.