Search Results (36)

Renicolid digeneans parasitise aquatic birds. In molecular trees, they are divided into three clades, one of which, the ‘duck clade’, parasitises anatids. Renicola mollissima, a member of this clade, parasitises sea ducks, mainly eiders. Its life cycle remains unknown. We verified the diagnosis of R. mollissima using integrated morphological and molecular data and provided the first information on its life cycle in northern Palaearctic. We proved that intramolluscan stages of R. mollissima, previously known as Cercaria pacifica 2, develop in intertidal snails Littorina squalida and L. saxatilis. We provided a detailed morphological description of cercariae and adults of R. mollissima and a discriminative analysis with closely related species. Molecular data demonstrated an amphiboreal distribution of R. mollissima and the existence of a single population in Europe and the North Pacific. Using molecular methods, we also found metacercariae of an unknown renicolid species from the ‘duck clade’, designated as Cercaria cf. nordica I, in subtidal mussels of the Barents Sea. All individuals of C. cf. nordica I examined in our study were represented by the same haplotype. We discuss possible ways of formation of this phylogeographic structure, the composition of the ‘duck clade’ and the evolutionary pathways of the family Renicolidae. Full article

Bivalves serve as the first intermediate hosts in the life cycles of some digeneans, but little is known about their larval stages along the southwestern Atlantic coast. These larvae may provide valuable insights into the ecological role of mollusks in parasite life cycles and marine food webs. This study offers a morphological, histological, and molecular (ITS2, 28S rDNA) description of the larval stages of three digenean species parasitizing the bivalve Jukesena foveolata in the Beagle Channel, Tierra del Fuego Province, Argentina. Sporocysts containing cercariae of a monorchiid species were found infecting the gonads and digestive glands (p = 2%), while metacercariae were encysted in the foot (p = 7%). Additionally, metacercariae of Renicola sp. (Renicolidae) were located between the tubules of the digestive gland (p = 2%), and metacercariae of Bartolius sp. (Gymnophallidae) were found in the extrapallial space (between the mantle and the valve, p = 13.5%), where they elicited a histopathological reaction with the secretion of a calcareous, igloo-shaped coating. The monorchiid larvae are described here for the first time in this bivalve, with fish as their definitive hosts. Metacercariae of Renicola sp. and Bartolius sp., both of which use coastal birds as definitive hosts, have been previously recorded in other mollusks from the Argentine coast. This study contributes to our understanding of the life cycles of digeneans from the southwestern Atlantic coast and the role of bivalve hosts in marine food webs. Full article

This study investigates the parasitic biodiversity of the fish species Astyanax bimaculatus and Psalidodon fasciatus in a stream located in the Chapada do Araripe Environmental Protection Area (APA), state of Ceará, Brazil, contributing to the understanding of parasitic fauna diversity of freshwater fish in neotropics. In total, 292 fish specimens were collected and analyzed, identifying 13 parasite taxa in A. bimaculatus and 11 in P. fasciatus. Several parasite groups were identified, including myxozoans, monogeneans, digeneans, and nematodes. The host A. bimaculatus exhibited a higher number of parasite taxa and abundance compared to P. fasciatus. The lower sample size for P. fasciatus reflects its naturally lower abundance in the wild, but the analyses accounted for sampling bias, ensuring comparisons of the parasite communities of these two fish species. The parasite communities of both species showed high similarity, indicating potential host-switching or co-evolutionary patterns. Positive correlations were observed between parasite diversity, species richness, abundance, and host weight/length. The study expands the knowledge of parasite–host associations and the geographical distribution of parasite species in Northeastern Brazil, a region where such data remain underreported. Full article

Leeches play a critical role in the transmission of digenean trematodes, yet their parasitic infections remain understudied in the Baltic region. This study investigates the diversity, prevalence, and molecular identification of trematode infections in freshwater leeches from central Lithuania. A total of five leech species (Alboglossiphonia heteroclita, Glossiphonia complanata, Glossiphonia verrucata, Helobdella stagnalis, and Erpobdella octoculata) were examined using compression and dissection techniques to detect trematode cysts, which were predominantly found in the soft tissues rather than the intestinal tract. Molecular sequencing of 18S rRNA, COI, and ITS markers, combined with phylogenetic analyses, confirmed the presence of three trematode genera: Cotylurus, Australapatemon, and Posthodiplostomum. The overall infection rate among leeches was 40.8%, with the highest prevalence observed in G. complanata (53.3%). Cotylurus spp. were the most frequently detected parasites, with genetic analyses revealing close affinities to Cotylurus syrius and Cotylurus spp. from Poland. Australapatemon species were also identified, though species-level classification remained inconclusive. Notably, this study provides the first molecular evidence of Posthodiplostomum cuticola utilizing leeches as intermediate hosts, extending the known range of hosts for this trematode. Phylogenetic analyses demonstrated the broad geographic distribution of these parasites, with close genetic matches to isolates from Poland, Russia, Canada, and Japan. The findings highlight the ecological significance of leeches in parasite transmission networks and contribute to the understanding of trematode diversity and host interactions in the Baltic region. Further molecular and ecological studies are needed to clarify species diversity and the role of leeches in the life cycles of aquatic parasites. Full article

Freshwater ecosystems in Lithuania are threatened by the introduction of invasive fish species including Neogobius fluviatilis, N. melanostomus, Perccottus glenii, and Pseudorasbora parva. Data on helminth parasites of these fishes have not been comprehensively studied, with only two reports on parasites of N. melanostomus from the Curonian Lagoon and Baltic Sea, Lithuania. We examined 278 fish individuals representing 4 invasive species from 13 waterbodies. Using morphological and molecular analyses, we identified 29 helminth taxa representing 15 digenean trematodes, 6 nematodes, 4 cestodes, 2 acanthocephalans, and 2 monogeneans. With 18 species, N. fluviatilis had the highest helminth diversity, followed by N. melanostomus (11 species) and Ps. parva (8 species). Perccottus glenii was found to be free from helminth infection. The availability of historical information on the native fish parasites in Lithuania allowed us to conclude that out of the 29 recorded species, invasive fish serve as hosts for 22 local fish helminth species, while 7 helminth species have been reported exclusively in invasive fish. Based on newly obtained and previously published data, a total of 34 helminth species parasitise invasive fish in Lithuania, of which 30 use these fish as intermediate or paratenic hosts. Full article

The study of sperm characteristics has proven useful for elucidating interrelationships in several groups of Platyhelminthes, such as digeneans. Thus, in the present work, the ultrastructural organization of the mature spermatozoon of the digenean Artyfechinostomum malayanum (Echinostomatidae), a parasite of Rattus norvegicus (Rodentia: Muridae) from Dong Thap Province, Vietnam, was investigated for the first time using transmission electron microscopy. The male gamete of A. malayanum exhibits two axonemes of different lengths, showing the 9 + ‘1’ pattern of the Trepaxonemata, a nucleus, two mitochondria, two lateral expansions, two bundles of parallel cortical microtubules, external ornamentation, spine-like bodies, and granules of glycogen. Thus, the mature spermatozoon follows a Type V sperm model proposed for digeneans. We also highlight some noteworthy characteristics in Echinostomatidae with possible phylogenetic implications, such as two lateral expansions in the anterior region of the spermatozoon and two mitochondria. Full article

The taxonomic status of many species of the family Cyclocoelidae is still unclear. Two species of cyclocoelids, Harrahium obscurum and Morishitium dollfusi, were collected from the air sacs of birds (Turdus merula and Tringa ochropus) inhabiting the Middle Volga region (European Russia). Here, we provide the first detailed morphological description of these cyclocoelids and combine it with the first molecular phylogenetic analysis of Cyclocoelidae from birds in Russia based on partial sequences of their 28s rDNA and coI mtDNA genes. Specimens of both flatworm species from different host individuals differ slightly in body shape and size, which probably reflects host-induced intraspecific variability. For the first time, we have shown that a stable morphological character such as the length of the vitelline fields in the studied digeneans is variable at the species level and cannot be used in their morphological diagnosis. Full article

Renicolids are parasites of aquatic birds. Their species identification based on morphological characters is problematic. Here, we revised the composition of Renicola spp. parasitising anatids in nearshore areas of northern seas using integrated morphological and molecular data. We redescribed Renicola somateria and verified the diagnosis of R. mediovitellata. We established that the first intermediate host (FIH) of R. somateria is the mollusc Buccinum undatum, while the FIHs of R. mediovitellata are Nucella spp. molluscs. We described the intramolluscan stages of both species. Renicola somateria and R. mediovitellata formed a separate clade in the molecular trees of the Renicolidae. This finding confirms the existence of three main phylogenetic branches of renicolids, differing in the structure of adults, type of cercariae, and host range. Molecular data demonstrated an amphiboreal distribution of both R. somateria and R. mediovitellata. The former is represented by a single population in Europe and the North Pacific, while the latter forms separate populations in these regions. This may be because R. somateria actually uses not only B. undatum but also some other buccinid species with similar circum-Arctic ranges as the FIH. We discuss the roles played in the formation of digenean ranges by the vagility of the definitive host, the lifespan of the adults, and the distribution of the FIH. Full article

The prevalence of endoparasites associated with chaetognath abundance in the coastal waters of the Mexican Central Pacific was studied fortnightly from November 2010 to December 2011. A total of 35 (0.21%) out of 16,407 chaetognaths were found to be parasitized. Five out of twelve chaetognath species (Flaccisagitta enflata, F. hexaptera, Parasagitta euneritica, Serratosagitta pacifica, Zonosagitta bedoti) were found to be parasitized by nine endoparasitic taxa: Protists (two morphotypes), digenean metacercariae [Didymozoidae, Hemiuridae, Parahemiurus sp., Lepocreadiidae, Prosorhynchus sp. (Bucephalidae)], and cestodes (metacestodes) [Tetraphyllidea (two morphotypes)]. Parasagitta. euneritica and Z. bedoti were the most abundant chaetognath species, and Protist sp. 2 and Tetraphyllidea sp. 1 were the most abundant parasites. The highest prevalence for most of the endoparasite species occurred in June, and the values varied according to three hydroclimatic periods: stratified (S), semi-mixed (SM), and mixed (M). Eight non-infected chaetognath species, two parasitized chaetognaths (F. enflata and S. pacifica), and two parasites (Protist sp. 1 and Tetraphyllidea sp. 2) were associated with warm temperatures (S and SM periods); in contrast, P. euneritica, Z. bedoti, parasitized F. hexaptera, and the parasite Tetraphyllidea sp. 1 showed a strong local preference for cooler temperatures, high productivity, and high biomass conditions (M periods). We discovered the occurrence of the digenean Prosorhynchus sp. (Bucephalidae) parasitizing the chaetognath P. euneritica, and this is the first report of Prosorhynchus parasitizing chaetognaths worldwide. We also confirmed the presence of Lepocrediidae (metacercariae larval stage) infecting F. hexaptera, a parasite that had only been recorded infecting other chaetognaths of the Atlantic Ocean. The parasite diversity affecting the chaetognath populations of the Central Mexican Pacific coast likely differs between the offshore, outer slope areas, and the surveyed coastal system. Full article

This study presents the first record of T. lindbergi from the southwestern Atlantic Ocean, based on specimens collected from the smalleye croaker Nebris microps Cuvier (Sciaenidae), off the coast of Maranhão Island, State of Maranhão, Brazil. Our approach included a morphological analysis complemented by DNA sequencing (28S, ITS2 rDNA, and cox1 mtDNA). Our phylogenetic analysis revealed the affinity of T. lindbergi to its congener T. laticaudi Parukhin, 1969, a digenean parasite commonly found in hydrophiine snakes inhabiting the Pacific Ocean. The interspecific divergence between T. lindbergi and T. laticaudi measures 3.80% for 28S, 7.49–7.64% for ITS2, and 16.29–16.70% for cox1. Our findings expand the documented geographic range of T. lindbergi into the southwestern Atlantic Ocean, report a novel host record, and increase the number of hemiurids known from Brazil to 30 species. Additionally, this study represents the initial documentation of a marine digenean fish within the North Brazil Shelf. Full article

Multiple factors can facilitate invasion success, with the absence of natural enemies, such as predators and parasites, recognised as conferring a significant advantage on invasive over native species. Pumpkinseed Lepomis gibbosus (Centrarchidae) represents one of the most successful freshwater fish invaders in Europe. Previous research has highlighted genetic differences between pumpkinseed populations in Türkiye and those in other European regions, attributed to rapid adaptation to new environmental conditions. This study aimed to investigate whether these highly adapted pumpkinseed populations in Türkiye benefit from a potential release from parasites, as proposed by the enemy-release hypothesis. Genetic characterisation of pumpkinseed populations from both European and Asian parts of Türkiye revealed that they share the same cytochrome c oxidase I haplotype as European populations. Microsatellite analysis indicated low genetic diversity, with STRUCTURE analysis confirming the clustering of all Turkish populations, suggesting a common source. Consistent with the low genetic diversity indicative of a small founding population, we observed a limited number of co-introduced parasite species, including the myxozoan Myxobolus dechtiari, the monogenean Onchocleidus dispar, and the digenean Posthodiplostomum centrarchi. Parasite infection by local parasites acquired in Türkiye was rare. Parasite diversity, species richness, and equitability were low, with only nine parasite taxa identified in all four pumpkinseed populations. The most diverse parasite community was found in Değirmenköy Reservoir, located in the European part of Türkiye, where seven parasite taxa were identified. While our study did not uncover genetically distinct pumpkinseed populations in Türkiye, the fish demonstrated resilience against most local parasite species, potentially providing them with an advantage over native species, aligning with the enemy-release hypothesis. Full article

Pomacea canaliculata is one of the most dangerous invasive species. Morphological and molecular analyses have revealed that a digenean species belonging to the family Echinostomatidae parasitizes this snail at two sites in Buenos Aires Province, Argentina, South America. Molecular results confirmed that the species belongs to a genus closely related to Patagifer. Analysis of the 28S rDNA showed that the sequences of the rediae and metacercariae are identical, indicating that the apple snail acts as the first and second intermediate host. The cercariae may encyst as metacercaria inside the redia and also emerge and re-infect the same snail or another snail. The prevalence of digeneans was higher in one of the sampling locations (15.1% vs. 0.72%), probably because the bird species that acts as the definitive host is more abundant in that area. Histopathological examination showed that the parasite quickly invades multiple host organs (gills, intestines, albumen gland, lung, kidney, and mantle border) besides the gonad and digestive gland, as is usual in digeneans. In addition, the partial or total castration of snails was observed in cases of moderate and high infection intensity. In males, there was loss of integrity in testicular tubules, while in females, the replacement of ovarian tissue by rediae was found. Full article

Schistosomiasis, acquired by skin-penetrating cercariae of dioecious digenean schistosomes during freshwater contact, afflicts nearly 260 and 440 million people with active infections and residual morbidity, respectively. About 10 million women at reproductive age contract schistosomiasis during gestation every year. Acute schistosomiasis is characterized by pre-patent pro-inflammatory CD4+ T-helper 1 or CD4+ Th1/T-helper 17 reactivity against immature schistosomulae. Chronic schistosomiasis is dominated by post-patent anti-inflammatory CD4+ T-helper 2 reactivity against ova epitopes. Flukes co-exist in immunocompetent definitive hosts as they are capable of evading their defense mechanisms. Preventive measures should be complemented by vaccination, inducing long-term protection against transmission, infection, and disease recurrence, given the latest advancements in schistosomal vaccines. Vaccines become pivotal when considering constraints of chemotherapy, i.e., lack of protection against re-infection, and evolving resistance or reduced sensitivity. Transmission models for human non-zoonotic schistosomiasis incorporating vaccination available in PubMed, Embase and Web of Science up to 31 December 2023 are presented. Besides conceptual model differences, predictions meant to guide decision- and policymaking reveal continued worm harboring that facilitates transmission besides residual infections. In addition, increased susceptibility to re-infection and rebound morbidity, both shifted to later life stages following the intervention, are forecasted. Consequently, a vaccination schedule is pivotal that considers the optimal age for initial immunization, i.e., pre-schoolchildren or schoolchildren in a cohort-based or population-based manner, while incorporating potential non-adherers promoting ongoing transmission. Longevity over magnitude of vaccine protection to antigenic schistosomal moieties is crucial. Accounting for pre-acquired immunity from natural exposure, in utero priming in addition to herd immunity, and induced by chemotherapy is crucial. Combining, as a multi-component approach, long-term effects of vaccination with short-term effects of chemotherapy as regular repeated vaccine-linked therapy seems most promising to achieve WHO’s endpoints of transmission elimination and morbidity control. Full article

Opecoeloides Odhner, 1928, is represented by 19 valid species found in marine fish, of which five have been reported in Brazil. Specimens of Opecoeloides pedicathedrae Travassos, Freitas & Bührnheim, 1966, were collected from the intestine of smooth weakfish Cynoscion leiarchus, a new host record, from off the coast of Rio de Janeiro, Brazil. They were examined using light and confocal laser microscopy. New partial sequences of 18S and 28S rDNA genes of O. pedicathedrae were obtained. Bayesian inference analysis on the partial 28S rDNA dataset resulted in a phylogram in which O. pedicathedrae formed a well-supported clade with Opecoeloides fimbriatus and Opecoeloides furcatus. The K2p distance between O. pedicathedrae and O. fimbriatus was 0.34%, with 3 divergent nucleotides; and between O. pedicathedrae and O. furcatus was 4.18%, with 38 divergent nucleotides. A Bayesian-inference phylogenetic tree based on the 18S rDNA recovered two main clades with five subfamilies. A clade of Opecoelinae showed that O. pedicathedrae was closer to Pseudopecoeloides tenuis; the K2p distance between these species was 2.14%, with 28 divergent nucleotides. The new nucleotide sequences presented inclusion of a phylogenetic analysis that can help to clarify the understanding of this complex taxon. Full article

Eurytrema coelomaticum, a pancreatic fluke, is recognized as a causative agent of substantial economic losses in ruminants. This infection, commonly referred to as eurytrematosis, is a significant concern due to its detrimental impact on livestock production. However, there is a paucity of knowledge regarding the mitochondrial genome of E. coelomaticum. In this study, we performed the initial sequencing of the complete mitochondrial genome of E. coelomaticum. Our findings unveiled that the mitochondrial genome of E. coelomaticum spans a length of 15,831 bp and consists of 12 protein-coding genes, 22 tRNA genes, two rRNA genes, and two noncoding regions. The A+T content constituted 62.49% of the genome. Moreover, all 12 protein-coding genes of E. coelomaticum exhibit the same arrangement as those of E. pancreaticum and other published species belonging to the family Dicrocoeliidae. The presence of a short string of additional amino acids (approximately 20~23 aa) at the N-terminal of the cox1 protein in both E. coelomaticum and E. pancreaticum mitochondrial genomes has contributed to the elongation of the cox1 gene in genus Eurytrema, surpassing that of all previously sequenced Dicrocoeliidae. The phylogenetic analysis displayed a close relationship between E. coelomaticum and E. pancreaticum, along with a genus-level association between Eurytrema and Lyperosomum. These findings underscore the importance of mitochondrial genomic data for comparative studies of Dicrocoeliidae and even Digenea, offering valuable DNA markers for future investigations in the systematic, epidemiological, and population genetic studies of this parasite and other digenean trematodes. Full article