Different metazoan parasites, different transcriptomic responses, with new insights on parasitic castration by digenetic trematodes in the schistosome vector snail Biomphalaria glabrata.

BACKGROUND: Gastropods of the genus Biomphalaria (Family Planorbidae) are exploited as vectors by Schistosoma mansoni, the most common causative agent of human intestinal schistosomiasis. Using improved genomic resources, overviews of how Biomphalaria responds to S. mansoni and other metazoan parasites can provide unique insights into the reproductive, immune, and other systems of invertebrate hosts, and their responses to parasite challenges. RESULTS: Using Illumina-based RNA-Seq, we compared the responses of iM line B. glabrata at 2, 8, and 40 days post-infection (dpi) to single infections with S. mansoni, Echinostoma paraensei (both digenetic trematodes) or Daubaylia potomaca (a nematode parasite of planorbid snails). Responses were compared to unexposed time-matched control snails. We observed: (1) each parasite provoked a distinctive response with a predominance of down-regulated snail genes at all time points following exposure to either trematode, and of up-regulated genes at 8 and especially 40dpi following nematode exposure; (2) At 2 and 8dpi with either trematode, several snail genes associated with gametogenesis (particularly spermatogenesis) were down-regulated. Regarding the phenomenon of trematode-mediated parasitic castration in molluscs, we define for the first time a complement of host genes that are targeted, as early as 2dpi when trematode larvae are still small; (3) Differential gene expression of snails with trematode infection at 40dpi, when snails were shedding cercariae, was unexpectedly modest and revealed down-regulation of genes involved in the production of egg mass proteins and peptide processing; and (4) surprisingly, D. potomaca provoked up-regulation at 40dpi of many of the reproduction-related snail genes noted to be down-regulated at 2 and 8dpi following trematode infection. Happening at a time when B. glabrata began to succumb to D. potomaca, we hypothesize this response represents an unexpected form of fecundity compensation. We also document expression patterns for other Biomphalaria gene families, including fibrinogen domain-containing proteins (FReDs), C-type lectins, G-protein coupled receptors, biomphalysins, and protease and protease inhibitors. CONCLUSIONS: Our study is relevant in identifying several genes involved in reproduction that are targeted by parasites in the vector snail B. glabrata and that might be amenable to manipulation to minimize their ability to serve as vectors of schistosomes.

Littorina snails and Microphallus trematodes: Diverse consequences of the trematode-induced metabolic shifts.

The intricate relationships between parasites and hosts encompass a wide range of levels, from molecular interactions to population dynamics. Parasites influence not only the physiological processes in the host organism, but also the entire ecosystem, affecting mortality of individuals, the number of offspring through parasitic castration, and matter and energy cycles. Understanding the molecular mechanisms that govern host-parasite relationships and their impact on host physiology and environment remains challenging. In this study, we analyzed how infection with Microphallus trematodes affects the metabolome of two Littorina snail species inhabiting different intertidal zone shore levels. We applied non-targeted GC-MS-based metabolomics to analyze biochemical shifts induced by trematode infection in a host organism. We have identified changes in energy, amino acid, sugar, and lipid metabolism. In particular, we observed intensified amino acid catabolism and nitrogenous catabolites (glutamine, urea) production. These changes primarily correlated with infection and interspecies differences of the hosts rather than shore level. The changes detected in the host metabolism indicate that other aspects of life may have been affected, both within the host organism and at a supra-organismal level. Therefore, we explored changes in microbiota composition, deviations in the host molluscs behavior, and acetylcholinesterase activity (ACE, an enzyme involved in neuromuscular transmission) in relation to infection. Infected snails displayed changes in their microbiome composition. Decreased ACE activity in snails was associated with reduced mobility, but whether it is associated with trematode infection remains unclear. The authors suggest a connection between the identified biochemical changes and the deformation of the shell of molluscs, changes in their behavior, and the associated microbiome. The role of parasitic systems formed by microphallid trematodes and Littorina snails in the nitrogen cycle at the ecosystem level is also assumed.

Season, size, and sex: factors influencing monogenean prevalence and intensity on Gambusia affinis in New Zealand.

A number of studies have been conducted on monogenean seasonality, though primarily in continental regions with wide annual temperatures ranges. We investigated seasonal changes in the prevalence and intensity of Salsuginus seculus infesting sexually dimorphic western mosquitofish (Gambusia affinis) in New Zealand. This represents the first examination of seasonality for this species globally, and the first seasonal assessment of any monogenean population in New Zealand, a temperate country with a mild oceanic climate. Prevalence and intensity of S. seculus with respect to fish size and sex was also examined. Prevalence of S. seculus changed temporally, peaking in summer, and was strongly positively correlated with algal concentrations. This relationship may be associated with increasing food levels, leading to an increase in fish courting and mating, resulting in high numbers and close physical associations of G. affinis individuals, facilitating transmission of the monogeneans. Thus, biotic factors may be important in determining temporal changes in S. seculus prevalence in New Zealand. Female G. affinis had a significantly higher prevalence and mean intensity of S. seculus than males. Longer fish had a higher mean intensity and prevalence of S. seculus. Female G. affinis likely host disproportionately more monogeneans as they are larger than males. Alternatively, females may have a compromised immune response during reproductive periods. Overall, seasonal change was observed in S. seculus prevalence and intensity under New Zealand's mild climatic conditions, and the larger female G. affinis in this dimorphic species supported a greater prevalence and intensity of infestation than males.

Immunology and pathology of echinostomes and other intestinal trematodes.

Intestinal trematodes constitute a major group of helminths that parasitize humans and animals with relevant morbidity and mortality. Despite the importance of the intestinal trematodes in medical and veterinary sciences, immunology and pathology of these helminth infections have been neglected for years. Apart from the work focused on the members of the family Echnistomatidae, there are only very isolated and sporadic studies on the representatives of other families of digeneans, which makes a compilation of all these studies necessary. In the present review, the most salient literature on the immunology and pathology of intestinal trematodes in their definitive hosts in examined. Emphasis will be placed on members of the echinostomatidae family, since it is the group in which the most work has been carried out. However, we also review the information on selected species of the families Brachylaimidae, Diplostomidae, Gymnophallidae, and Heterophyidae. For most of these families, coverage is considered under the following headings: (i) Background; (ii) Pathology of the infection; (iii) Immunology of the infection; and (iv) Human infections.

One Health monitoring reveals invasive freshwater snail species, new records, and undescribed parasite diversity in Zimbabwe.

BACKGROUND: Snail-borne trematodes afflict humans, livestock, and wildlife. Recognizing their zoonotic potential and possible hybridization, a One Health approach is essential for effective control. Given the dearth of knowledge on African trematodes, this study aimed to map snail and trematode diversity, focusing on (i) characterizing gastropod snail species and their trematode parasites, (ii) determining infection rates of snail species as intermediate hosts for medically, veterinary, and ecologically significant trematodes, and (iii) comparing their diversity across endemic regions. METHODS: A cross-sectional study conducted in 2021 in Chiredzi and Wedza districts in Zimbabwe, known for high human schistosomiasis prevalence, involved malacological surveys at 56 sites. Trematode infections in snails were detected through shedding experiments and multiplex rapid diagnostic polymerase chain reactions (RD-PCRs). Morphological and molecular analyses were employed to identify snail and trematode species. RESULTS: Among 3209 collected snail specimens, 11 species were identified, including schistosome and fasciolid competent snail species. We report for the first time the invasive exotic snail Tarebia granifera in Zimbabwe, which was highly abundant, mainly in Chiredzi, occurring at 29 out of 35 sites. Shedding experiments on 1303 snails revealed a 2.24% infection rate, with 15 trematode species identified through molecular genotyping. Five species were exclusive to Chiredzi: Bolbophorus sp., Schistosoma mansoni, Schistosoma mattheei, Calicophoron sp., and Uvulifer sp. Eight were exclusive to Wedza, including Trichobilharzia sp., Stephanoprora amurensis, Spirorchid sp., and Echinostoma sp. as well as an unidentified species of the Plagiorchioidea superfamily. One species, Tylodelphys mashonensis, was common to both regions. The RD-PCR screening of 976 non-shedding snails indicated a 35.7% trematode infection rate, including the presence of schistosomes (1.1%) Fasciola nyanzae (0.6%). In Chiredzi, Radix natalensis had the highest trematode infection prevalence (33.3%), while in Wedza, R. natalensis (55.4%) and Bulinus tropicus (53.2%) had the highest infection prevalence. CONCLUSIONS: Our xenomonitoring approach unveiled 15 trematode species, including nine new records in Zimbabwe. Schistosoma mansoni persists in the study region despite six mass deworming rounds. The high snail and parasite diversity, including the presence of exotic snail species that can impact endemic species and biomedically important trematodes, underscores the need for increased monitoring.

Understanding the host response of farmed fish to blood flukes (Trematoda: Aporocotylidae) for developing new treatment strategies.

Aporocotylids (Trematoda: Digenea), also known as fish blood flukes infect the circulatory system of fish leading to serious health problems and mortality. Aporocotylids are a particular concern for farmed fish as infection intensity can increase within the farming environment and lead to mortalities. In the context of managing these infections, one of the most crucial aspects to consider is the host response of the infected fish against these blood flukes. Understanding the response is essential to improving current treatment strategies that are largely based on the use of anthelmintic praziquantel to manage infections in aquaculture. This review focuses on the current knowledge of farmed fish host responses against the different life stages of aporocotylids. New treatment strategies that are able to provide protection against reinfections should be a long-term goal and is not possible without understanding the fish response to infection and the interactions between host and parasite.

Morphological and molecular characterization of brown-banded broodsacs and metacercariae of Leucochloridium (Trematoda: Leucochloridiidae) parasitizing the semi-slug Omalonyx unguis (Succineidae) in Argentina.

Trematodes of the genus Leucochloridium exhibit an unusual transmission strategy among mollusks (intermediate host). The fully developed sporocyst, housing encysted metacercariae, displays vivid coloration and rhythmic activity in the snail's tentacle, mimicking insect larvae. These strategies attract insectivorous birds, their final hosts, thereby increasing the chances of completing their life cycle. In South America, the reports of adults and larval stages of Leucochloridium are scarce. Brown-banded broodsac of Leucochloridium sp. were obtained from Omalonyx unguis collected in a shallow lake from Corrientes Province, Argentina. Here, we morphologically characterized the larval stages (broodsac and metacercaria), identified the parasite through DNA sequences from nuclear 28S-rRNA (28S) and the mitochondrial cytochrome c oxidase I (COI) genes, and explored its evolutionary affinities with the Leucochloridium species available in GenBank. The present broodsac displays brown bands, with a yellowish background in the first two-thirds and yellowish-white in the last third. Based on morphological comparisons, the broodsac and metacercaria described in this study could not be conclusively categorized under any known South American species of Leucochloridium. In relation to the phylogenetic reconstructions, Leucochloridium sp. consistently clustered with L. perturbatum, and species delimitation analyses resulted in recognized Leucochloridium sp. from Argentina as a distinct species. The DNA sequences obtained in this study constitute the first genetic data generated for sporocyst broodsacs in South America. Future studies, incorporating morphology, genetic, and biological data, will be essential for both species identification and the elucidation of leucochloridiid diversity in the region.

Characterisation of Nematoda and Digenea in selected Australian freshwater snails.

Freshwater snails are integral to local ecosystems as a primary food source for various vertebrate species, thereby contributing significantly to ecological food webs. However, their role as intermediate hosts also makes them pivotal in the transmission of parasites. In Australia, research on freshwater snails has predominantly focused on their role as intermediate hosts for livestock parasites, while there has been limited exploration of the impact of these parasites on snail health and population dynamics. The aim of this study was to determine parasitic infection in freshwater snails. This study was conducted in the south-eastern region of Australia, in 2022. A total of 163 freshwater snails from four different species were collected and examined in the Murrumbidgee catchment area in the southeastern part of Australia during the Southern Hemisphere summer and autumn months (February to May). The species included Isidorella hainesii, Glyptophysa novaehollandica, Bullastra lessoni (endemic species), and Physella acuta (an introduced species). Through the analysis of sequence data from the various regions of the nuclear ribosomal DNA, we determined that the Digenea species in this study belonged to three distinct species, including Choanocotyle hobbsi, Petasiger sp. and an unidentified species belonging to Plagiorchioidea. Additionally, analysis of the sequences from Nematoda found in this study, revealed they could be categorized into two separate taxa, including Krefftascaris sp. and an unidentified nematode closely associated with plant and soil nematodes. This research holds significant implications for the future understanding and conservation of Australian freshwater ecosystems. Most parasites found in the present study complete their life cycle in snails and turtles. As many of freshwater snail and turtle species in Australia are endemic and face population threats, exploring the potential adverse impacts of parasitic infections on snail and turtle health, is crucial for advancing our understanding of these ecosystems and also paving the way for future research and conservation efforts. While none of the native snail species in the present study have been listed as endangered or threatened, this may simply be attributed to the absence of regular population surveys.

Behave yourself: effects of exogenous-glucocorticoid exposure on larval amphibian anti-parasite behaviour and physiology.

Parasites represent a ubiquitous threat for most organisms, requiring potential hosts to invest in a range of strategies to defend against infection-these include both behavioural and physiological mechanisms. Avoidance is an essential first line of defence, but this behaviour may show a trade-off with host investment in physiological immunity. Importantly, while environmental stressors can lead to elevated hormones in vertebrates, such as glucocorticoids, that can reduce physiological immunity in certain contexts, behavioural defences may also be compromised. Here, we investigate anti-parasite behaviour and immune responses against a trematode (flatworm) parasite by larval amphibians (tadpoles) exposed or not to a simulated general stressor in the form of exogenous corticosterone. Tadpoles that were highly active in the presence of the trematode infectious stage (cercariae) had lower infection loads, and parasite loads from tadpoles treated only with dechlorinated water were significantly lower than those exposed to corticosterone or the solvent control. However, treatment did not affect immunity as measured through white blood-cell profiles, and there was no relationship between the latter and anti-parasite behaviour. Our results suggest that a broad range of stressors could increase host susceptibility to infection through altered anti-parasite behaviours if they elevate endogenous glucocorticoids, irrespective of physiological immunity effects. How hosts defend themselves against parasitism in the context of multiple challenges represents an important topic for future research, particularly as the risk posed by infectious diseases is predicted to increase in response to ongoing environmental change.

Parvatrema spp. (Digenea, Gymnophallidae) with parthenogenetic metacercariae: diversity, distribution and host specificity in the palaearctic.

There are several species of gymnophallid digeneans in the genus Parvatrema that are unique in developing metacercariae that reproduce by parthenogenesis in the second intermediate host. Transmission of these digeneans takes place in coastal ecosystems of the North Pacific and North Atlantic seas. The first intermediate hosts are bivalves, the second ones are gastropods, and the definitive hosts are migratory birds. We integrated data accumulated over 25 years of research and differentiated a complex of five closely related species. They differ in the molluscan second intermediate hosts, distribution ranges, and life cycles patterns. The type I life cycle includes two generations of parthenogenetic metacercariae, followed by development of metacercariae which are invasive for the definitive host. In the type II life cycle, the number of generations of parthenogenetic metacercariae is unlimited, and they can also produce cercariae. These cercariae emerge into the environment and can infect new individuals of the second intermediate host. We conclude that the type I life cycle is a derived option that has evolved as a better fit to transmission in the unstable conditions in the intertidal zone. Another evolutionary trend in Parvatrema is transition from inhabiting the extrapallial space of the gastropod second intermediate host to endoparasitism in its mantle and internal organs. rDNA sequence analysis highlighted that Parvatrema spp. with parthenogenetic metacercariae form a monophyletic clade and suggested the Pacific origin of the group, with two transfers to the North Atlantic and colonisation of new second intermediate host species. Apparently the group formed in the late Pliocene-Pleistocene and diversified as a result of recurrent isolation in inshore refugia during glacial periods. We argue that parthenogenetic metacercariae in Parvatrema may serve as a model for early digenean evolution, demonstrating the first steps of adopting the molluscan first intermediate host and becoming tissue parasites.

One-health approach on the future application of snails: a focus on snail-transmitted parasitic diseases.

Snails are fascinating molluscs with unique morphological and physiological adaptive features to cope with various environments. They have traditionally been utilized as food and feed sources in many regions of the world. The future exploitation of alternative nutrient sources, like snails, is likely to increase further. Snails, however, also serve as an intermediate host for several zoonotic parasites. A category of parasitic infections, known as snail-transmitted parasitic diseases (STPDs), is harmful to humans and animals and is mainly driven by various trematodes, cestodes, and nematodes. The environment plays a crucial role in transmitting these parasites, as suitable habitats and conditions can facilitate their growth and proliferation in snails. In light of diverse environmental settings and biologically categorized snail species, this review evaluates the dynamics of significant STPDs of zoological importance. Additionally, possible diagnostic approaches for the prevention of STPDs are highlighted. One-health measures must be considered when employing snails as an alternative food or feed source to ensure the safety of snail-based products and prevent any adverse effects on humans, animals, and the environment.

No time to relax: Age-dependent infectivity of cercariae in marine coastal ecosystems.

Age dynamics of the ability of cercariae of two digenean species, Himasthla elongata (Himasthlidae) and Renicola parvicaudatus (Renicolidae), to infect the second intermediate host (SIH), mussels (Mytilus edulis), was investigated experimentally. This is the first study of this kind made on cercariae transmitted in the intertidal of the northern seas. The larvae of all tested ages (from 0.5 to 6 hr) were equally successful in infecting mussels. This finding disagrees with the literature data on cercariae of several freshwater digeneans, which are practically incapable of infecting the SIH during the first 1-3 hr of life. The presence of a time delay before the attainment of the maximum infectivity (TDMI) may be associated with the need for physiological maturation of cercariae in the very beginning of their life in the environment, the need for their broad dispersion, and the prevention of superinfection of the downstream host. The absence of TDMI in the cercariae examined in our study could be associated with the instability of environmental factors in the marine intertidal (wave impact, tidal currents). These factors promote a broad dispersion of cercariae in the intertidal biotope and prevent superinfection of potential SIHs. Biological and behavioural features may also play a role. We hypothesize that the presence or absence of TDMI does not depend on the taxonomic affiliation of the cercariae but is determined by the transmission conditions.

Manipulative neuroparasites: uncovering the intricacies of neurological host control.

Manipulative neuroparasites are a fascinating group of organisms that possess the ability to hijack the nervous systems of their hosts, manipulating their behavior in order to enhance their own survival and reproductive success. This review provides an overview of the different strategies employed by manipulative neuroparasites, ranging from viruses to parasitic worms and fungi. By examining specific examples, such as Toxoplasma gondii, Leucochloridium paradoxum, and Ophiocordyceps unilateralis, we highlight the complex mechanisms employed by these parasites to manipulate their hosts' behavior. We explore the mechanisms through which these parasites alter the neural processes and behavior of their hosts, including the modulation of neurotransmitters, hormonal pathways, and neural circuits. This review focuses less on the diseases that neuroparasites induce and more on the process of their neurological manipulation. We also investigate the fundamental mechanisms of host manipulation in the developing field of neuroparasitology, which blends neuroscience and parasitology. Finally, understanding the complex interaction between manipulative neuroparasites and their hosts may help us to better understand the fundamentals of behavior, neurology, and host-parasite relationships.

Species of Hexabothriidae (Monogenea) may have extensive distribution ranges reflecting multiple host species: evidence from three new South African records.

Many hexabothriid genera require renewed taxonomic attention to provide additional detailed comparative data from new material to resolve existing species quandaries. Our current study describes and provides additional museum material for three hexabothriid species from three genera from South Africa: Erpocotyle catenulata (Guberlet), which is confirmed as a valid species, Heteronchocotyle gymnurae Neifar, Euzet and Ben Hassine, and Hypanocotyle bullardi Chero, Cruces, Sáez, Carolina, Camargo, Portes Santos and Luque. Evidence of these three hexabothriid species from South Africa suggests that hexabothriids have more globally widespread distributions, and that they are less host-specific than previously considered. A detailed summary of hexabothriids reported from the triakid hosts, Galeorhinus galeus and Mustelus mustelus is provided, and the host-specificity of hexabothriids is discussed.

Effect of predation risk on parasite transmission from first to second intermediate trematode hosts.

Predators can affect parasite-host interactions when directly preying on hosts or their parasites. However, predators may also have non-consumptive indirect effects on parasite-host interactions when hosts adjust their behaviour or physiology in response to predator presence. In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. Laboratory experiments revealed that chemical cues from crabs lead to a threefold increase in the release of trematode cercariae from periwinkles as a result of increased periwinkle activity. This positive effect on transmission was contrasted by a 10-fold reduction in cercarial infection rates in the second intermediate host when we experimentally exposed mussels to cercariae and predator cues. The low infection rates were caused by a substantial reduction in mussel filtration activity in the presence of predator cues, preventing cercariae from entering the mussels. To assess the combined net effect of both processes, we conducted a transmission experiment between infected periwinkles and uninfected mussels. Infection levels of mussels in the treatments with crab cues were sevenfold lower than in mussels without crab chemical cues. This suggests that predation risk effects on mussel susceptibility can counteract the elevated parasite release from first intermediate hosts, with negative net effects on parasite transmission. These experiments highlight that predation risk effects on parasite transmission can have opposing directions at different stages of the parasite's life cycle. Such complex non-consumptive predation risk effects on parasite transmission may constitute an important indirect mechanism affecting prevalence and distribution patterns of parasites in different hosts across their life cycle.

Diversity of trematodes from the amphibian anomaly P hotspot: Role of planorbid snails.

Trematode infection of the second intermediate hosts can lead to changes in their fitness and, as a result, a change in the invasion rate of animal communities. It is especially pronounced during the invasion of parasite species that reduce activity due to the manipulation of hosts through the changes of their morphology and physiology. One of these cases is an anomaly P syndrome hotspot found in some populations of water frogs and toads in Europe caused by the trematode Strigea robusta metacercariae. The occurrence of pathogen and their participation in ecosystems are intrigues questions in the anomaly P phenomenon, as well as the role of planorbid snails that serve as the first intermediate hosts for many trematode species. Herein, we focused on trematodes spectra from planorbid snails and amphibians from the anomaly P hosts with the aim to undetected interactions between the pathways of parasites. Emerging cercariae of 6802 planorbid snails of dominant species (Planorbarius corneus, Planorbis planorbis, and Anisus spp.) were detected by both morphological and molecular methods in seven waterbodies in Privolzhskaya Lesostep Nature Reserve (Russia). A total of 95 sequences of 18 species were received, and 48 sequences were unique and did not present in any genetic databases. The 18 species of trematodes from snails and 14 species of trematodes from amphibian hosts (Pelophylax ridibundus; Ranidae; Anura) were detected. Three species (Echinostoma nasincovae, Tylodelphys circibuteonis and Australapatemon burti) was new for the trematode fauna of the Middle Volga River region and Russia as a whole. Eleven species of parasitic flatworms have amphibians in their life cycles and nine species used amphibians as metacercariae hosts: Echinostoma nasincovae, E. miyagawai, Echinoparyphium recurvatum, Tylodelphys circibuteonis, Neodiplostomum spathula, Paralepoderma cloacicola, Macrodera longicollis, Strigea robusta, and Strigea strigis. The occurrence of trematode species from planorbid mollusks and frogs were compared.

Clinostomum complanatum: Anthelmintic potential of curcumin on the infective progenetic metacercarial stage.

The emerging resistance against commonly used antiparasitic drugs has driven investigators to explore alternative approaches using plant-derived active ingredients. These compounds have been tested for antiviral, antibacterial, and anthelmintic properties, particularly against adult worms. However, their effects on larval forms have been neglected. Curcumin is a polyphenol that is a significant constituent of the rhizome of Curcuma longa and possesses various biological activities, including antioxidant, anti-inflammatory, anti-infectious, and anti-carcinogenic. In the present study, the anthelmintic potential of curcumin was tested in vitro for its efficacy against the zoonotically important larval form, the progenetic metacercariae of Clinostomum complanatum, which were procured from the forage fish, Trichogaster fasciatus. Curcumin produced time and concentration-dependent inhibition in the motility of treated metacercarial worms, with the maximum inhibition of motility reported at 60 µM along with a significant increase of (36-92%) in ROS and (57-112%) in GSH levels at the end of a period of 6 h. In contrast, curcumin at the highest concentration significantly inhibited the activities of the antioxidant and detoxification enzymes SOD (36%) and GST (16%), respectively, in addition to altering the polypeptide profile and inhibiting cysteine proteases. The tegumental surface appeared to be highly disrupted in curcumin-treated worms, exhibiting severe blebbing, shearing of the tegument, and spine erosion. Such changes would affect the tegumental functions and survival of worms in the hostile microenvironment. This would render worms more susceptible to host-mediated rejection responses. Based on the results of the present study, it is inferred that C. complanatum could serve as an excellent model for screening novel anthelmintic drugs against larval trematodes of great economic significance. Furthermore, we conclude that curcumin could be exploited as an excellent phytotherapeutic agent against the virulent larval form under investigation.

Effects of metacercariae of Prosorhynchoides sp. (Trematoda: Bucephalidae) on the swimming ability and blood parameters of the intertidal fish Girella laevifrons (Osteichthyes: Kyphosidae).

Parasites may have various effects on their host's health. It is important to determine the type of the effects but also to decipher the physiological mechanisms underlying a parasitic infection. In this study, swimming ability (by a fixed swim speed test) and haematological analyses (by blood parameters) were compared between juvenile fish Girella laevifrons non-parasitised and parasitised with metacercariae of Prosorhynchoides sp. Fish were infested in the laboratory using natural parasitised mussels. Aerobic swimming time, total erythrocyte and leukocyte counts were compared among four groups of fish: non-parasitised (NP), non-parasitised but manipulated (NPM), parasitised 3 days (PT1), and 10 days (PT2) post-infection. Differentiated haematological components were also compared among NP, PT1 and PT2 fish groups. Parasitised fish (PT1 and PT2) swam between 32% and 55% less time than unparasitised fish. Erythrocyte counts were lower in PT1, indicating anemia, and total leukocyte counts were higher in PT1, showing immune action. Macrophages and basophils were observed only in parasitised fish, independent of the post-infection time. There was a negative correlation between swimming time and leukocyte counts. Increased leukocytes in the blood indicate activation of the innate cellular immune response, which may be metabolically costly for the host. Moreover, the anemia in parasitised fish would reduce the oxygen transport necessary to carry out aerobic exercise, reducing the swimming capacity. In fish several days post-infection (PT2), the erythrocytes count reached normal values, and some kinds of leukocytes decreased in comparison to fish PT1. This suggests that parasitised fish with metacercariae were recovering.

Land snails can trap trematode cercariae in their shell: Encapsulation as a general response against parasites?

Terrestrial gastropods are hosts of a wide variety of metazoan parasites and can respond to parasite exposure in various ways. One of these defence mechanisms, the ability to trap parasites in the host shell, was previously thought to apply only against nematodes. During a field survey along an urbanisation gradient, we found that the shell of Cornu aspersum and Cepaea nemoralis can contain encapsulated trematode cercariae, with prevalences of 7% and 1%, respectively over the entire sample, and up to 47% at the local population level. To our knowledge, this is the first case study unambiguously showing that land snails can trap non-nematode parasites in their shell at non-negligible prevalences. Shell-encapsulation could be a more general defence mechanism than previously described, and more studies are needed to understand its importance and variability.

Title: Les gastéropodes terrestres peuvent piéger les cercaires de trématodes dans leur coquille : l'encapsulation comme réponse générale contre les parasites ? Abstract: Les gastéropodes terrestres sont les hôtes d'une grande variété de métazoaires parasites, et peuvent répondre de plusieurs façons à l'exposition parasitaire. L'un de ces mécanismes de défense, la capacité à piéger le parasite dans la coquille, semblait ne concerner que les nématodes. Lors d'un suivi de terrain le long d'un gradient d'urbanisation, nous avons observé que la coquille de Cornu aspersum et de Cepaea nemoralis pouvait contenir des cercaires de trématodes encapsulées, à des prévalences respectives de 7 % et 1 % sur l'ensemble de l'échantillon, et pouvant atteindre 47 % au niveau d'une population locale. À notre connaissance, ceci est la première étude montrant sans ambiguïté que les escargots terrestres peuvent piéger de façon significative des parasites autres que les nématodes dans leur coquille. L'encapsulation des parasites dans la coquille pourrait donc être un mécanisme de défense plus général que précédemment décrit, plus d'études étant nécessaires pour comprendre son importance et sa variabilité.

First record of trace element accumulation in a freshwater ectoparasite, Paradiplozoon ichthyoxanthon (Monogenea; Diplozoidae), infecting the gills of two yellowfish species, Labeobarbus aeneus and Labeobarbus kimberleyensis.

BACKGROUND: Elevated levels of trace elements in the aquatic environment poses risks to the health of biota and humans. Parasites are important components in ecosystems; responding to changes in the health of aquatic ecosystems and can accumulate trace elements in their tissues to higher levels than their hosts. Monogeneans are an important group of fish ectoparasites being directly exposed to the aquatic environment. METHODS: In this study concentrations of Ti, Fe, Cu, Zn, Rb, Sr and Ag were analysed in the monogenean parasite, Paradiplozoon ichthyoxanthon (by total reflection x-ray fluorescence spectrometry and graphite furnace atomic absorption spectrometry), and the muscle, liver and gills of two host fish species, Labeobarbus aeneus and Labeobarbus kimberleyensis (by inductively coupled plasma -- mass spectrometry). RESULTS: Most striking was the accumulation pattern for Zn in parasites; mean levels of Zn were as high as 1448 and 1652 mg kg-1 dw, respectively, with no significant difference between the two host-parasite groups, leading to bioconcentration factors of approximately 93 (parasite/fish muscle) and 15 (parasite/fish liver). In addition, Fe was accumulated in the parasite to a higher degree compared to the fish hosts' tissues. Cu levels were higher in P. ichthyoxanthon than in the muscle tissue of both host fishes, but lower than liver tissue. CONCLUSION: These findings demonstrate the usefulness of this parasite species as a sentinel organism in aquatic ecosystems it inhabits for Fe and Zn. Other trace elements under investigation were not accumulated higher in the parasite compared to its fish host. Lower Rb levels in the parasite compared to its hosts indicate no biomagnification of this metal. Further investigations are required to determine if similar trends in trace element accumulation occur in other monogeneans. DATA AVAILABILITY: All data generated in the analysis of host and parasite tissues are presented in the manuscript.