Thermal tolerance and survival are modulated by a natural gradient of infection in differentially acclimated hosts.

Wild ectotherms are exposed to multiple stressors, including parasites, that can affect their responses to environmental change. Simultaneously, unprecedented warm temperatures are being recorded worldwide, increasing both the average and maximum temperatures experienced in nature. Understanding how ectotherms, such as fishes, will react to the combined stress of parasites and higher average temperatures can help predict the impact of extreme events such as heat waves on populations. The critical thermal method (CTM), which assesses upper (CTmax) and lower (CTmin) thermal tolerance, is often used in acclimated ectotherms to help predict their tolerance to various temperature scenarios. Despite the widespread use of the CTM across taxa, few studies have characterized the response of naturally infected fish to extreme temperature events or how acute thermal stress affects subsequent survival. We acclimated naturally infected pumpkinseed sunfish (Lepomis gibbosus) to four ecologically relevant temperatures (10, 15, 20 and 25°C) and one future warming scenario (30°C) for 3 weeks before measuring CTmax and CTmin. We also assessed individual survival the week following CTmax. Parasites were counted and identified following trials to relate infection intensity to thermal tolerance and survival. Interestingly, trematode parasites causing black spot disease were negatively related to CTmax, suggesting that heavily infected fish are less tolerant to acute warming. Moreover, fish infected with yellow grub parasites showed decreased survival in the days following CTmax implying that the infection load has negative survival consequences on sunfish during extreme warming events. Our findings indicate that, when combined, parasite infection and high prolonged average temperatures can affect fish thermal tolerance and survival, emphasizing the need to better understand the concomitant effects of stressors on health outcomes in wild populations. This is especially true given that some parasite species are expected to thrive in warming waters making host fish species especially at risk.

Large-scale spatial drivers of avian schistosomes in Northern Michigan inland lakes.

Avian schistosomes are snail-borne trematode parasites (Trichobilharzia spp.) that can cause a nasty skin rash in humans when their cercariae mistake us for their normal bird hosts. We sought to investigate drivers of the spatial distribution of Trichobilharzia cercaria abundance throughout Northern Michigan lakes. For 38 sites on 16 lakes, we assessed several dozen potential environmental predictors that we hypothesized might have direct or indirect effects on overall cercaria abundance, based on known relationships between abiotic and biotic factors in wetland ecosystems. We included variables quantifying local densities of intermediate hosts, temperature, periphyton growth rates, human land use and hydrology. We also measured daily abundance of schistosome cercariae in the water over a 5-week period, supported by community scientists who collected and preserved filtered water samples for qPCR. The strongest predictor of cercaria abundance was Lymnaea host snail density. Lymnaea density was higher in deeper lakes and at sites with more deciduous tree cover, consistent with their association with cool temperature habitats. Contrary to past studies of human schistosomes, we also found a significant negative relationship between cercaria abundance and submerged aquatic vegetation, possibly due to vegetation blocking cercaria movement from offshore snail beds. If future work shows that these effects are indeed causal, then these results suggest possible new approaches to managing swimmer's itch risk in northern MI lakes, such as modifying tree cover and shallow-water vegetation at local sites.

Integrative taxonomy of metazoan parasites of the bluntnose sixgill shark Hexanchus griseus (Bonnaterre, 1788) in the Mediterranean Sea, with the resurrection of Grillotia acanthoscolex Rees, 1944 (Cestoda: Trypanorhyncha).

Appropriate diagnoses of parasites of apex marine predators are crucial to understand their biodiversity, host specificity, biogeography, and life cycles. Such diagnoses are also informative of ecological and biological characteristics of both host and environment in which the hosts and their parasites live. We here (i) investigate the parasite fauna of a bluntnose sixgill shark Hexanchus griseus (Bonnaterre, 1788) obtained from the Gulf of Naples (Tyrrhenian Sea), (ii) characterize molecularly all its metazoan parasites, and (iii) resurrect and report the main morphological features and phylogenetic position of Grillotia acanthoscolex, a cestode species previously synonymized with Grillotia adenoplusia. A rich parasite fauna represented by eight different taxa was found, including two monogeneans (Protocotyle grisea and Protocotyle taschenbergi), one digenean (Otodistomum veliporum), four cestodes (Crossobothrium dohrnii, Clistobothrium sp., G. acanthoscolex, and G. adenoplusia), and one copepod (Protodactylina pamelae). Sequencing of these samples accounts for an important molecular baseline to widen the knowledge on the parasitic fauna of bluntnose sixgill sharks worldwide and to reconstruct their correct food chains. The bluntnose sixgill shark was found to be a definitive host for all endoparasites found here, confirming that it occupies an apex trophic level in the Mediterranean Sea. The taxa composition of the trophic parasite fauna confirms that the bluntnose sixgill shark mostly feeds on teleost fish species. However, the occurrence of two phillobothrid cestodes (C. dohrnii and Clistobothrium sp.) suggests that it also feeds on squids. Finally, we emphasize the importance of using integrative taxonomic approaches in the study of parasites from definitive and intermediate hosts to elucidate biology and ecology of taxa generally understudied in the Mediterranean Sea.

Idiopyrgus souleyetianus (Gastropoda: Tomichiidae) as an intermediate host of the liver fluke Amphimerus sp. (Trematoda: Opisthorchiidae) in Brazil.

Despite the importance of fish-borne trematodes of the family Opisthorchiidae as causative agents of human liver fluke disease, studies on these parasites outside Asia are relativally scarce. In South America, human focus of amphimerosis is known in Ecuador since the mid-20th century, and Amphimerus spp. have also been reported in wild and domestic mammals. Nevertheless, the knowledge on the snails that act as the first intermediate host of these potentially zoonotic parasites are scarce. Herein, a new cercaria of the pleurolophocercous morphotype found in the freshwater snail Idiopyrgus souleyetianus from Brazil was subjected to morphological and molecular studies. Multigene phylogenetic analyses based on 28S, 5.8S-ITS-2 and Cox-1 sequences enabled the identification of Amphimerus sp., a species distinct from that reported in humans from Ecuador. This cercariae was morphologically compared with other opisthorchiid cercariae known. The possible occurrence of human amphimerosis in Brazil is discussed.

Effectiveness of health education in improving knowledge, attitude and practice related to foodborne zoonotic trematodes in Vietnam, with a particular focus on Clonorchis sinensis.

OBJECTIVE: Foodborne zoonotic trematodes (FZT), which infect the liver, lungs and intestines of humans, are an emerging public health concern in tropical countries including Vietnam. In northern Vietnam, Clonorchis sinensis is recognised as the most important species of the FZT. Up to now, small-scale studies conducted in the country have indicated that health education could improve participants' knowledge and practices related to clonorchiasis, however strong evidence is still lacking. We conducted an intervention trial between 2020 and 2021 in four communes in Yen Bai and Thanh Hoa province, aiming to evaluate the impact of an extended educational package on knowledge, attitude and practices related to clonorchiasis, as well as on knowledge on the large liver fluke and minute intestinal flukes. METHODS: To this end, baseline and post-intervention questionnaires were conducted. Generalised estimating equations models were run to analyse the impact of the intervention on knowledge, attitudes and practices over time in the intervention versus control group. Finally, 172 people in the intervention group and 162 in the control group were included for analysis. RESULTS: Results demonstrated that the intervention significantly improved clonorchiasis knowledge, attitudes and practices, with higher odds for a correct knowledge response (odds ratio (OR) = 2.80, 95% confidence interval (CI) = 1.84-4.27, p-value < 0.001), increased average mean attitude score (mean = 0.363, 95%CI = 0.182-0.544, p-value < 0.001), and a reduced odds of consuming raw fish (OR = 0.15, 95%CI = 0.06-0.40, p = 0.002) in the intervention group compared to the control group post-intervention versus baseline. Additionally, participants in the intervention group exhibited enhanced basic knowledge of the large liver fluke and minute intestinal flukes post-intervention. CONCLUSIONS: These findings demonstrate the potential of health education programs in preventing clonorchiasis in endemic areas, emphasising the importance of continued health education as a critical component of integrated control programs for clonorchiasis.

Phylogenetic relationship of Prohemistomum vivax to other trematodes based on the internal transcribed spacer region and mitochondrial genes.

Prohemistomum vivax is a zoonotic small cyathocotylid trematode that inhabits the intestines of fish-eating birds and mammals. Here, we amplified the internal transcribed spacer (ITS) sequence and six mitochondrial protein-coding genes (PCGs) from P. vivax. The ITS region was 1389 base pairs long and had a partial 18S ribosomal RNA gene, a full ITS1, 5.8S rRNA, and ITS2 sequence, and a partial 28S rRNA gene. The ITS region of P. vivax showed a minimum pairwise distance (0.3-0.6%) from the ITS sequences of Cyathocotylidae sp. 1 and 2 metacercariae from Clarias gariepinus. This result suggests that these metacercariae belong to P. vivax metacercariae. We first amplified mitochondrial genes from P. vivax, including cytochrome c oxidase subunit III (cox3) partial sequence; tRNA-His, cytochrome b (cytb), and NADH dehydrogenase subunit 4L (nad4L) complete sequences; and NADH dehydrogenase subunit 4 (nad4), cytochrome c oxidase I (cox1), and NADH dehydrogenase subunit 5 (nad5) partial sequences. P. vivax was most closely related to Cyathocotyle prussica (NC_039780) and Holostephanus sp. (OP082179), with cox1, cox3, and cytb genes conserved among the three trematodes. The ML phylogenetic tree of ITS sequences supports the order Diplostomida, divided into two main clades (the superfamily Diplostomoidea and Schistosomatoidea). The phylogeny of concatenated amino acid sequences of P. vivax six PCGs revealed that diplostomoids and Clinostomum sp. evolved in a clade with Plagiorchiida members, away from Schistosoma species. These results may yield ribosomal and mitochondrial genetic markers for molecular epidemiological investigations of cyathocotylid intestinal flukes.

Detection of echinostomatid trematode eggs at the forest-oil palm interface in Sabah, Malaysia.

In this study, we report the occurrence of echinostomatid eggs in feces of wildlife, domestic animals and humans frequenting the forest­oil palm plantation interface in the Kinabatangan (Sabah, Malaysia), and discuss potential implications for public health. Using microscopy, we detected echinostomatid eggs in six host species, including Asian palm civets (Paradoxurus hermaphroditus [13/18]), leopard cats (Prionailurus bengalensis [3/4]), long-tailed macaques (Macaca fascicularis [1/10]), domestic dogs [3/5] and cats [1/1], and humans [7/9]. Molecular analysis revealed a close genetic proximity of civet echinostomatids to Artyfechinostomum malayanum, a zoonotic parasite of public health relevance. The intermediate hosts for A. malayanum have been reported in at least 3 districts in Sabah, suggesting that all the necessary elements required for the completion of the parasite's life cycle are present. Our findings point at the presence of zoonotic trematodes in an area with high human­wildlife interaction and highlight the potential public and animal health concern of zoonotic trematode infection in the context of Southeast Asia's rapidly changing ecosystems.

Trace elements assessment in Cerastoderma glaucum from port areas in the Tunisian Mediterranean coast: The influence of parasites on bioaccumulation.

In the present study, the seasonal concentration of seven trace elements was investigated in sediment and the cockle Cerastoderma glaucum tissues from two port areas in the North-East and South of Tunisia comparing cockles non-parasitized (NP) and parasitized (P) with digenean parasites. Elements concentration in sediments analyzed in both sites revealed that Zinc (Zn), Chromium (Cr), and Lead (Pb) were the most abundant ones, while Cadmium (Cd) and Mercury (Hg) were less abundant. The bioaccumulation of trace metals and Arsenic (As) in the tissues of cockles seems to be modulated by both the infection state and the parasite species. The relationship between bioaccumulation of metals and As, trematode species and abiotic parameters showed that the availability of certain metals for uptake by P cockles of both sites was influenced by the salinity and temperature of the water. Our results corroborate the possibility of using digenean infecting bivalves in biomonitoring aquatic ecosystems.

Disturbance and disease: host-parasite interactions in freshwater streams remain stable following wildfire.

Increases in the intensity and frequency of wildfires highlight the need to understand how fire disturbance affects ecological interactions. Though the effects of wildfire on free-living aquatic communities are relatively well-studied, how host-parasite interactions respond to fire disturbance is largely unexplored. Using a Before-After-Control-Impact design, we surveyed 10 stream sites (5 burned and 5 unburned) in the Willamette River Basin, Oregon and quantified snail host infection status and trematode parasite community structure 1 year before and two years after historic wildfires. Despite the severity of the wildfires, snail host populations did not show significant shifts in density or size distributions. We detected nine taxa of trematode parasites and overall probability of infection remained consistent over the three-year study period. However, at the taxon-specific level, we found evidence that infection probability by one trematode decreased and another increased after fire. In a larger dataset focusing on the first year after fire (9 burned, 8 unburned sites), we found evidence for subtle differences in trematode community structure, including higher Shannon diversity and evenness at the burned sites. Taken together, host-parasite interactions were remarkably stable for most taxa; for trematodes that did show responses, changes in abundance or behavior of definitive hosts may underlie observed patterns. These results have implications for using parasites as bioindicators of environmental change and suggest that aquatic snail-trematode interactions may be relatively resistant to wildfire disturbance in some ecosystems.

Trematode parasites as indicators of an animal component in the diet of the Water Vole Arvicola amphibius.

The intestinal trematode fauna of the Water Vole Arvicola amphibius, (previously A. terrestris), was investigated to determine whether it might provide evidence of an animal component in the diet of this aquatic herbivorous small mammal. Interrogation of the electronic Host-Parasite Database of the Natural History Museum London revealed the presence of fourteen species of intestinal trematode in water voles, infection with each of which would require the ingestion of tissue from an animal intermediate host. The results obtained using these parasite indicators provide convincing evidence of animal components in the diet of A. amphibius and support anecdotal reports of water voles feeding on animal material in the field.

Prevalence of Foodborne Trematodes in Small Indigenous Fish Species in Local Markets of Phnom Penh, Cambodia.

Background: This study aimed to determine the prevalence and mean infection intensity of zoonotic foodborne trematodes (FBT) in small indigenous species (SIS) fish hosts. Materials and Methods: A total of 8630 specimens of unknown origin were collected from the markets in Phnom Penh City. Fish were identified, weighed, and separated into 20 g subsamples for each fish species, and were examined using the artificial digestion method. A total of 10 species of FBT were detected in 11 species of fish out of the 23 species of fish in the total sample. Results: All infected FBT species were intestinal flukes. No liver flukes were found. The overall prevalence of FBT infection was 29.3% ± 5.3%, and the mean intensity was 0.85 ± 1.89 metacercariae (Mc)/g. The highest FBT prevalence was observed for Isthmiophora hortensis (10.7%) and Centrocestus formosanus (7.9%). Other species identified were Diplostomum spp., Echinochasmus japonicus, Echinostoma revolutum, Echinostoma sudanense, Haplorchis taichui, Haplorchis pumilio Heterophyes spp., and Procerovum varium. The highest mean intensity was found for Diplostomum spp. (1.75 ± 3.03 Mc/g). Trichopsis vittata was one of the main species constituting the SIS in urban markets (31.72%) and showed the highest prevalence of FBT (75.0%). In addition, T. vittata had the highest diversity of intestinal flukes compared with other fish species. Amblypharyngodon chulabhornae showed the highest mean intensity. but low diversity (only two species) and low prevalence. Conclusions: T. vittata could be considered a potential indicator for targeted monitoring of FBT intestinal flukes, but A. chulabhornae could also be considered for quantitative studies considering its high mean intensity.

A Molecular Phylogenetic Study of the Eye Fluke Philophthalmus lacrymosus (Trematoda: Philophthalmidae) Found in Larus dominicanus (Aves: Laridae) from Brazil.

PURPOSE: Species of the genus Philophthalmus are eye flukes with a complex taxonomy, which began to be improved with the help of molecular data only recently. However, most described species have never been placed into a phylogenetic context. In this study, eye flukes previously found on kelp gulls, Larus dominicanus, from Brazil and identified as Philophthalmus lacrymosus were subjected to molecular analysis. METHODS: For the molecular analyses, we analyzed parasites found in six infected gulls (one worm per bird) collected from different municipalities of the state of Santa Catarina, Brazil. We carried out the amplification and sequencing of the partial region of the 28S and cox1 genes and the data obtained were compared with sequences available to philophthalmid species and subjected to phylogenetic analysis. RESULTS: The isolates of P. lacrymosus from Brazil grouped in well-supported clades with five other species of Philophthalmus with sequences available for comparison. Interspecific divergences of 0.1-1.6% in 28S and 8.2-14.9% in cox1 were found in relation to other isolates of Philophthalmus spp. Two cox1 haplotypes differing in one nucleotide (0.1%) were found between the six eye flukes isolates in gulls from different localities. The Brazilian isolates grouped in a subclade with parasites identified as P. lacrymosus in Portugal; however, the molecular divergences found in cox1 (8.2-8.5%) strongly suggest that these isolates belong to different species. The phylogenetic trees obtained and the intergeneric divergences to species of the genera Cloacitrema and Parorchis did not support the validity of the genus Natterophthalmus, for which P. lacrymosus was proposed as the type species in the past. CONCLUSION: As P. lacrymosus was described from Brazil, we recommend that this name be applied to the South American isolates and that the Portuguese isolates be provisionally considered as Philophthalmus sp., a probable cryptic species. Moreover, data obtained supports the previous morphology-based synonymizing between Natterophthalmus and Philophthalmus. Considering our results and most of previous reports of P. lacrymosus in South America, we suggest this species presents a marine life cycle.

Glycan Complexity and Heterogeneity of Glycoproteins in Somatic Extracts and Secretome of the Infective Stage of the Helminth Fasciola hepatica.

Fasciola hepatica is a global helminth parasite of humans and their livestock. The invasive stage of the parasite, the newly excysted juvenile (NEJs), relies on glycosylated excreted-secreted (ES) products and surface/somatic molecules to interact with host cells and tissues and to evade the host's immune responses, such as disarming complement and shedding bound antibody. While -omics technologies have generated extensive databases of NEJs' proteins and their expression, detailed knowledge of the glycosylation of proteins is still lacking. Here, we employed glycan, glycopeptide, and proteomic analyses to determine the glycan profile of proteins within the NEJs' somatic (Som) and ES extracts. These analyses characterized 123 NEJ glycoproteins, 71 of which are secreted proteins, and allowed us to map 356 glycopeptides and their associated 1690 N-glycan and 37 O-glycan forms to their respective proteins. We discovered abundant micro-heterogeneity in the glycosylation of individual glycosites and between different sites of multi-glycosylated proteins. The global heterogeneity across NEJs' glycoproteome was refined to 53 N-glycan and 16 O-glycan structures, ranging from highly truncated paucimannosidic structures to complex glycans carrying multiple phosphorylcholine (PC) residues, and included various unassigned structures due to unique linkages, particularly in pentosylated O-glycans. Such exclusive glycans decorate some well-known secreted molecules involved in host invasion, including cathepsin B and L peptidases, and a variety of membrane-bound glycoproteins, suggesting that they participate in host interactions. Our findings show that F. hepatica NEJs generate exceptional protein variability via glycosylation, suggesting that their molecular portfolio that communicates with the host is far more complex than previously anticipated by transcriptomic and proteomic analyses. This study opens many avenues to understand the glycan biology of F. hepatica throughout its life-stages, as well as other helminth parasites, and allows us to probe the glycosylation of individual NEJs proteins in the search for innovative diagnostics and vaccines against fascioliasis.

Infection with Trematodes in Littorina obtusata Snails (Gastropoda: Littorinidae) with Different Shell Color Genotypes.

The prevalence of infection with trematode parthenitae was studied in Littorina obtusata littoral periwinkles with different shell color genotypes. Activities of genes responsible for a purple or orange single-pigment background shell coloration was not found to affect the prevalence of trematode infection in periwinkles. In L. obtusata with a yellow-purple background shell color and a pattern of white pigment spots on the shell, the prevalence of infection with Microphallus piriformes and M. pygmaeus was lower than the theoretical expectation. The prevalence of infection in periwinkles with purple, orange, or white stripes on the shell did not differ from that of unstripped periwinkles. The differences found were presumably associated with genetically determined susceptibility to infection. Possible consequences of differential infection with trematodes in periwinkles with different shell color genotypes are discussed in terms of the stability of parasitic systems and possible changes in the phenotypic structure of the host population.

Finding of an Unusually Colored Sporocyst of the Genus Leucochloridium in a Succinea putris Snail.

A Leucochloridium sp. Carus, 1835 sporocyst with a mature colored broodsac was found in a Succinea putris L., 1758 snail in the Boksitogorsk district of Leningrad Region (Russia). The pigmentation of the sporocyst's broodsac was different from those of other Leucochloridium Carus, 1835 species previously described for Europe. The obtained sporocyst is most similar by the coloration of its broodsac to the trematodes of the same genus from Japan. The genotyping of the investigated sporocyst by the rDNA gene fragments (complete ITS1, ITS2, 5.8S and partial 18S and 28S sequences) was conducted. Genetic distances between the obtained sporocyst and the previously described species of the genus Leucochloridium were higher than intraspecific ones in the most cases. These data and the data of morphological analysis imply that the investigated sporocyst belongs to a separate species of the Leucochloridium genus, previously not described in the European region.

Molecular confirmation of pearl formation in arctic mussels (Mytilus edulis) caused by Gymnophallus bursicola (Odhner 1900) metacercariae.

In recent field studies, suspected gymnophallid metacercariae were histologically located in the mantle of mussels from the Norwegian Sea. Mussels from the sites in which that infection was detected also presented abnormally high pearl numbers. It has been previously described that gymnophallid metacercariae could cause pearl formation processes in mussels, as a host reaction to encapsulate these metacercariae. Given the pathological host reaction these parasites elicit, a study was performed to identify gymnophallid metacercariae found in mussels collected from Tromsø at morphological and molecular level and to assess, by the use of molecular tools, the relationship between the parasite and the biological material inside the pearls. As a result, Gymnophallus bursicola metacercariae infecting Norwegian Mytilus edulis were identified according to morphological characters, along with the first 18S rDNA and COI sequences for this trematode species. In addition, parasite DNA from the core of the pearls was extracted and amplified for the first time, confirming the parasitological origin of these pearls. This procedure could allow identifying different parasitic organisms responsible for the generation of pearls in bivalves.

Prevalence of flukes (Fasciola hepatica and paramphistomids) in cattle in south-eastern Mexico.

The objective of this study was to determine the risk factors and prevalence of trematodes in south-eastern Mexico. The prevalence of trematodes was determined in 1010 bovines. The study was carried out from October 2018 (n=291) to December 2019 (n=719). Only in 2019 rumen and liver fluke eggs were differentiated. Faecal samples (n=311) were obtained from farms in southeast Mexico located in Tabasco, Chiapas and Campeche. In addition, the presence of flukes in liver and rumen from slaughtered cattle in abattoirs was recorded with a total of 408 samples. A logistic procedure was used to obtain the prevalence and the effect of main risk factors such as land physiography (flooded areas and hills), year, sex, animals' age and type of sample obtained (eggs in faeces and flukes). The general prevalence of flukes in cattle was 32.3 % in 2018 and 41.7 % in 2019. Prevalence of F. hepatica (liver fluke) was 18.6 % (134/719) and that of paramphistomids (rumen fluke) was 33.4 % (240/719). The infected cattle from the slaughterhouse indicated a lower prevalence of F. hepatica (1 %) and rumen fluke (26.7 %) than in farms detected by egg in faeces (41.8 % and 42.1 %, respectively). The physiographic zone was decisive in the presence of F. hepatica and rumen fluke, while sex did not represent a risk factor (P > 0.05). The environmental conditions of the Mexican southeast favour the presence of both liver and rumen fluke.

Helminth Fauna of Juvenile Green Sea Turtles (Chelonia mydas) from Rio de Janeiro State, Brazil.

The helminth fauna of juvenile green sea turtles (Chelonia mydas Linnaeus, 1758) is still poorly known. Herein, we study the gastrointestinal helminths of 28 juvenile green sea turtles found stranded on the north coast of Rio de Janeiro state, Brazil. All turtles were infected showing a rich helminth fauna. In total, 14802 trematodes belonging to 30 species and 5 families including Micros-caphidiidae, Plagiorchiidae, Pronocephalidae, Hapalotrematidae, and Telorchiidae were recovered. An unidentified nematode specimens was also found. The mean intensity was 536 (95% CI = 362 - 853) (range: 1 - 2831), and the species richness was 7.86 (95% CI = 6.46 - 9.21) (range: 1 - 17). The coast of Rio de Janeiro state represents new locality records for Angiodictyum posterovitellatum, Microscaphidium aberrans, M. warui, Octangium hyphalum, O. sagitta, Enodiotrema reductum and Pleurogonius laterouterus. This study confirms that the green sea turtle harbors the richest helminth fauna among sea turtle species and provides useful information on the gastrointestinal helminths of a poorly known stage in the life cycle of this endangered chelonian.

The impact of climate change and pollution on trematode-bivalve dynamics.

Coastal ecosystems and their marine populations are increasingly threatened by global environmental changes. Bivalves have emerged as crucial bioindicators within these ecosystems, offering valuable insights into biodiversity and overall ecosystem health. In particular, bivalves serve as hosts to trematode parasites, making them a focal point of study. Trematodes, with their life cycles intricately linked to external factors, provide excellent indicators of environmental changes and exhibit a unique ability to accumulate pollutants beyond ambient levels. Thus, they act as living sentinels, reflecting the ecological condition of their habitats. This paper presents a comprehensive review of recent research on the use of bivalve species as hosts for trematodes, examining the interactions between these organisms. The study also investigates the combined impact of trematode infections and other pollutants on bivalve molluscs. Trematode infections have multifaceted consequences for bivalve species, influencing various aspects of their physiology and behavior, including population-wide mortality. Furthermore, the coexistence of trematode infections and other sources of pollution compromises host resistance, disrupts parasite transmission, and reduces the abundance of intermediate hosts for complex-living parasites. The accumulation process of these parasites is influenced not only by external factors but also by host physiology. Consequently, the implications of climate change and environmental factors, such as temperature, salinity, and ocean acidification, are critical considerations. In summary, the intricate relationship between bivalves, trematode parasites, and their surrounding environment provides valuable insights into the health and sustainability of coastal ecosystems. A comprehensive understanding of these interactions, along with the influence of climate change and environmental parameters, is essential for effective management and conservation strategies aimed at preserving these delicate ecosystems and the diverse array of species that rely on them.

Molecular evidence of the absence of Metagonimus yokogawai (Katsurada, 1912) in Europe: report of Metagonimus sp. in cyprinoid fish from the River Danube in Hungary.

Trematodes of the genus Metagonimus Katsurada, 1912 (Digenea: Heterophyidae) are zoonotic parasites that cause infections in humans, with most cases reported in Southeast Asia. Larvae from the second intermediate host, called metacercariae, of one of human-infecting species, M. yokogawai (Katsurada, 1912), have been reported from cyprinoid fish in Europe. In the present study, we provided DNA-based evidence that metacercariae of Metagonimus, which are commonly found in the scales of various cyprinoids in Central Europe (Danube River in Hungary) do not belong to M. yokogawai. Sequence analysis of the ITS region, 28S rDNA, and cox1 genes showed that this species is clearly distinct from all Asian species, including M. yokogawai, which probably does not occur in Europe. Metacercariae from cyprinoids might belong to Metagonimus romanicus (Ciurea, 1915), an insufficiently known species described from Romania.