Impact of Schistosoma sp., Infection on Biological, Feeding, Physiological, Histological, and Genotoxicological Aspects of Biomphalaria alexandrina and Bulinus truncatus Snails.

BACKGROUND: Trematode infections of the genus Schistosoma can induce physiological and behavioral changes in intermediate snail hosts. This is because the parasite consumes essential resources necessary for the host's survival, prompting hosts to adapt their behavior to maintain some level of fitness before parasite-induced mortality occurs. METHODS: In this study, the reproductive and biochemical parameters of Biomphalaria alexandrina and Bulinus truncatus were examined during the cercareal shedding stage of infection with Schistosoma mansoni and Schistosoma haematobium, respectively, compared with controls. RESULTS: The study revealed an infection rate of 34.7% for S. mansoni and 30.4% for S. haematobium. In B. alexandrina infected with S. mansoni, a survival rate of 65.2% was recorded, along with a mean prepatent period of 30.3 ± 1.41 days, a mean shedding duration of 14.2 ± 0.16 days, and a mean lifespan of 44.1 ± 0.24 days. Meanwhile, in B. truncatus infected with S. haematobium, a survival rate of 56.4% was observed, with a mean prepatent period of 44.3 ± 1.41 days, a mean shedding duration of 22.6 ± 2.7 days, and a mean lifespan of 66.9 ± 1.6 days. Feeding increased in both infected species of snails, while the net reproductive rate (Ro) of the infected snails decreased. Total antioxidant (TAO) and lipid peroxidation activity increased in the two infected snail species during shedding, while Glutathione-S-transferase levels decreased. Lipid peroxidase activity and nitrogen oxide levels significantly decreased in infected B. alexandrina and increased in infected Bulinus. Steroid hormone levels were elevated in infected Biomphalaria, whereas they were reduced in infected Bulinus. Comet assay parameters showed an increase in the two infected genera after infection compared to control snails, indicating genotoxic damage and histopathological damage was observed. CONCLUSIONS: These findings demonstrate that infection with larva species diverse biochemical, hormonal, genotoxic, and histopathological changes in the tissues responsible for fecundity and reproduction in B. alexandrina and B. truncates comparing with controls.

A machine learning approach for modeling the occurrence of the major intermediate hosts for schistosomiasis in East Africa.

Schistosomiasis, a prevalent water-borne disease second only to malaria, significantly impacts impoverished rural communities, primarily in Sub-Saharan Africa where over 90% of the severely affected population resides. The disease, majorly caused by Schistosoma mansoni and S. haematobium parasites, relies on freshwater snails, specifically Biomphalaria and Bulinus species, as crucial intermediate host (IH) snails. Targeted snail control is advisable, however, there is still limited knowledge about the community structure of the two genera especially in East Africa. Utilizing a machine learning approach, we employed random forest to identify key features influencing the distribution of both IH snails in this region. Our results reveal geography and climate as primary factors for Biomphalaria, while Bulinus occurrence is additionally influenced by soil clay content and nitrogen concentration. Favorable climate conditions indicate a high prevalence of IHs in East Africa, while the intricate connection with geography might signify either dispersal limitations or environmental filtering. Predicted probabilities demonstrate non-linear patterns, with Bulinus being more likely to occur than Biomphalaria in the region. This study provides foundational framework insights for targeted schistosomiasis prevention and control strategies in the region, assisting health workers and policymakers in their efforts.

Exploring the immune interactions between Oncomelania hupensis and Schistosoma japonicum, with a cross-comparison of immunological research progress in other intermediate host snails.

Schistosomiasis, the second largest parasitic disease in the world after malaria, poses a significant threat to human health and causes public health issues. The disease primarily affects populations in economically underdeveloped tropical regions, earning it the title of "neglected tropical disease". Schistosomiasis is difficult to eradicate globally if medication alone is used. One of the essential elements of thorough schistosomiasis prevention and control is the management and disruption of the life cycle of intermediate host snails. The key approach to controlling the transmission of schistosomiasis is to control the intermediate hosts of the schistosome to disrupt its life cycle. We believe that approaching it from the perspective of the intermediate host's immunity could be an environmentally friendly and potentially effective method. Currently, globally significant intermediate host snails for schistosomes include Oncomelania hupensis, Biomphalaria glabrata, and Bulinus truncatus. The immune interaction research between B. glabrata and Schistosoma mansoni has a history of several decades, and the complete genome sequencing of both B. glabrata and B. truncatus has been accomplished. We have summarized the immune-related factors and research progress primarily studied in B. glabrata and B. truncatus and compared them with several humoral immune factors that O. hupensis research focuses on: macrophage migration inhibitory factor (MIF), Toll-like receptors (TLRs), and thioredoxin (Trx). We believe that continued exploration of the immune interactions between O. hupensis and Schistosoma japonicum is valuable. This comparative analysis can provide some direction and clues for further in-depth research. Comparative immunological studies between them not only expand our understanding of the immune defense responses of snails that act as intermediaries for schistosomes but also facilitate the development of more comprehensive and integrated strategies for schistosomiasis prevention and control. Furthermore, it offers an excellent opportunity to study the immune system of gastropods and their co-evolution with pathogenic organisms.

Fluorescent non transgenic schistosoma to decipher host-parasite phenotype compatibility.

Schistosomiasis is considered as a significant public health problem, imposing a deeper understanding of the intricate interplay between parasites and their hosts. Unfortunately, current invasive methodologies employed to study the compatibility and the parasite development impose limitations on exploring diverse strains under various environmental conditions, thereby impeding progress in the field. In this study, we demonstrate the usefulness for the trematode parasite Schistosma mansoni, leveranging a fluorescence-imaging-based approach that employs fluorescein 5-chloromethylfluorescein diacetate (CMFDA) and 5-chloromethylfluorescein diacetate (CMAC) as organism tracker for intramolluscan studies involving the host snail Biomphalaria glabrata. These probes represent key tools for qualitatively assessing snail infections with unmatched accuracy and precision. By monitoring the fluorescence of parasites within the snail vector, our method exposes an unprecedented glimpse into the host-parasite compatibility landscape. The simplicity and sensitivity of our approach render it an ideal choice for evolutionary studies, as it sheds light on the intricate mechanisms governing host-parasite interactions. Fluorescent probe-based methods play a pivotal role in characterizing factors influencing parasite development and phenotype of compatibility, paving the way for innovative, effective, and sustainable solutions to enhance our understanding host-parasite immunobiological interaction and compatibility.

Bioactivity of substances isolated from natural products on mollusks Biomphalaria glabrata (Say, 1818) (Planorbidae): a review.

Schistosomiasis is a neglected tropical disease caused by parasitic worms of several species of the genus Schistosoma. Transmission occurs by parasitic larvae that stay in freshwater snails of the genus Biomphalaria. Thus, the search for new products that are biodegradable has increased the interest in products of plant origin. The aim of this article is to review the isolated substances from natural products that showed molluscicidal activity against the species Biomphalaria glabrata in order to reevaluate the most promising prototypes and update the progress of research to obtain a new molluscicide. We perform searches using scientific databases, such as Scientific Electronic Library Online (SciELO), Google schoolar, PUBMED, Web of Science and Latin American and Caribbean Literature on Health Sciences (LILACS). From 2000 to 2022, using the keywords "isolated substances", "molluscicidal activity" and "Biomphalaria glabrata". In the present study, it was possible to observe 19 promising molluscicidal molecules with a lethal concentration below 20 µg/mL. Of these promising isolates, only 5 isolates had the CL90 calculated and within the value recommended by WHO: Benzoic acid, 2',4',6'-Trihydroxydihydrochalcone, Divaricatic acid, Piplartine and 2-hydroxy-1,4-naphthoquinone (Lapachol). We conclude that beyond a few results in the area, the researches don't follow the methodological pattern (exposure time and measure units, toxicity test), in this way, as they don't follow a pattern on the result's exposure (LC), not following, in sum, the recommended by WHO.

The FMRF-NH2 gated sodium channel of Biomphalaria glabrata: Localization and expression following infection by Schistosoma mansoni.

The neglected tropical disease schistosomiasis impacts over 700 million people globally. Schistosoma mansoni, the trematode parasite that causes the most common type of schistosomiasis, requires planorbid pond snails of the genus Biomphalaria to support its larval development and transformation to the cercarial form that can infect humans. A greater understanding of neural signaling systems that are specific to the Biomphalaria intermediate host could lead to novel strategies for parasite or snail control. This study examined a Biomphalaria glabrata neural channel that is gated by the neuropeptide FMRF-NH2. The Biomphalaria glabrata FMRF-NH2 gated sodium channel (Bgl-FaNaC) amino acid sequence was highly conserved with FaNaCs found in related gastropods, especially the planorbid Planorbella trivolvis (91% sequence identity). In common with the P. trivolvis FaNaC, the B. glabrata channel exhibited a low affinity (EC50: 3 x 10-4 M) and high specificity for the FMRF-NH2 agonist. Its expression in the central nervous system, detected with immunohistochemistry and in situ hybridization, was widespread, with the protein localized mainly to neuronal fibers and the mRNA confined to cell bodies. Colocalization of the Bgl-FaNaC message with its FMRF-NH2 agonist precursor occurred in some neurons associated with male mating behavior. At the mRNA level, Bgl-FaNaC expression was decreased at 20 and 35 days post infection (dpi) by S. mansoni. Increased expression of the transcript encoding the FMRF-NH2 agonist at 35 dpi was proposed to reflect a compensatory response to decreased receptor levels. Altered FMRF-NH2 signaling could be vital for parasite proliferation in its intermediate host and may therefore present innovative opportunities for snail control.

No evidence for schistosome parasite fitness trade-offs in the intermediate and definitive host.

BACKGROUND: The trematode parasite Schistosoma mansoni uses an aquatic snail intermediate and a vertebrate definitive host to complete its life cycle. We previously showed that a key transmission trait-the number of cercariae larvae shed from infected Biomphalaria spp. snails-varies significantly within and between different parasite populations and is genetically controlled by five loci. We investigated the hypothesis that the success of parasite genotypes showing high propagative fitness in the intermediate snail host may be offset by lower reproductive fitness in the definitive vertebrate host. METHODS: We investigated this trade-off hypothesis by selecting parasite progeny producing high or low number of larvae in the snail and then comparing fitness parameters and virulence in the rodent host. We infected inbred BALB/c mice using two Schistosoma mansoni parasite lines [high shedder (HS) and low shedder (LS) lines] isolated from F2 progeny generated by genetic crosses between SmLE (HS parent) and SmBRE (LS parent) parasites. We used the F3 progeny to infect two populations of inbred Biomphalaria glabrata snails. We then compared life history traits and virulence of these two selected parasite lines in the rodent host to understand pleiotropic effects of genes determining cercarial shedding in parasites infecting the definitive host. RESULTS: HS parasites shed high numbers of cercariae, which had a detrimental impact on snail physiology (measured by laccase-like activity and hemoglobin rate), regardless of the snail genetic background. In contrast, selected LS parasites shed fewer cercariae and had a lower impact on snail physiology. Similarly, HS worms have a higher reproductive fitness and produced more viable F3 miracidia larvae than LS parasites. This increase in transmission is correlated with an increase in virulence toward the rodent host, characterized by stronger hepato-splenomegaly and hepatic fibrosis. CONCLUSIONS: These experiments revealed that schistosome parasite propagative and reproductive fitness was positively correlated in intermediate and definitive host (positive pleiotropy). Therefore, we rejected our trade-off hypothesis. We also showed that our selected schistosome lines exhibited low and high shedding phenotype regardless of the intermediate snail host genetic background. ​.

A genome sequence for Biomphalaria pfeifferi, the major vector snail for the human-infecting parasite Schistosoma mansoni.

BACKGROUND: Biomphalaria pfeifferi is the world's most widely distributed and commonly implicated vector snail species for the causative agent of human intestinal schistosomiasis, Schistosoma mansoni. In efforts to control S. mansoni transmission, chemotherapy alone has proven insufficient. New approaches to snail control offer a way forward, and possible genetic manipulations of snail vectors will require new tools. Towards this end, we here offer a diverse set of genomic resources for the important African schistosome vector, B. pfeifferi. METHODOLOGY/PRINCIPAL FINDINGS: Based largely on PacBio High-Fidelity long reads, we report a genome assembly size of 772 Mb for B. pfeifferi (Kenya), smaller in size than known genomes of other planorbid schistosome vectors. In a total of 505 scaffolds (N50 = 3.2Mb), 430 were assigned to 18 large linkage groups inferred to represent the 18 known chromosomes, based on whole genome comparisons with Biomphalaria glabrata. The annotated B. pfeifferi genome reveals a divergence time of 3.01 million years with B. glabrata, a South American species believed to be similar to the progenitors of B. pfeifferi which undertook a trans-Atlantic colonization < five million years ago. CONCLUSIONS/SIGNIFICANCE: The genome for this preferentially self-crossing species is less heterozygous than related species known to be preferential out-crossers; its smaller genome relative to congeners may similarly reflect its preference for selfing. Expansions of gene families with immune relevance are noted, including the FReD gene family which is far more similar in its composition to B. glabrata than to Bulinus truncatus, a vector for Schistosoma haematobium. Provision of this annotated genome will help better understand the dependencies of trematodes on snails, enable broader comparative insights regarding factors contributing to susceptibility/ resistance of snails to schistosome infections, and provide an invaluable resource with respect to identifying and manipulating snail genes as potential targets for more specific snail control programs.

Evaluation of molluscicidal activity on Biomphalaria glabrata (Say, 1818) and phytochemical characterization of hydroalcoholic extract of leaves of Ricinus communis L. (EUPHORBIACEAE).

Schistosomiasis is a parasitic infection of great prevalence worldwide, affecting 250 million people in 78 countries. Faced with this problem, studies that seek to analyze molluscicidal activity from plant extracts have stood out. The present work aimed to obtain the phytochemical characterization and investigate the molluscicidal activity in the hydroalcoholic extract of Ricinus communis leaves on Biomphalaria glabrata. The hydroalcoholic extract was prepared by macerated with solvent ethanol P.A 96%, followed by filtration and concentration in rotary evaporator. Next, five groups of snails with 10 animals each, one being the negative control group, were submitted to treatments with four concentrations of 25, 50, 75 and 100 mg/L of hydroalcoholic extract of R. communis. The parameters mortality, physiological and behavioral aspects of mollusks were analyzed during 96h. The chemical characterization of the extract was performed by high-performance liquid chromatography coupled to mass spectrometry (LC-MS). Chemical characterization revealed the presence of tannins, flavonoids and ricinin alkaloid, but under the conditions analyzed, the presence of saponins was not observed. There was no significant molluscicidal activity of the extract. However, a greater influence was observed in the diet, in addition to the motility and physiological state of the snails (alteration of cephalopodal mass and oviposition). The toxicity test was performed with Artemia salina and no toxicity was observed for this microcrustacean. It is expected that the results obtained contribute to the fight against the expansion of schistosomiasis and that they make room for other studies that investigate the molluscicidal action of plant extracts.

Time series analysis of tegument ultrastructure of in vitro transformed miracidium to mother sporocyst of the human parasite Schistosoma mansoni.

The transformation of Schistosoma mansoni miracidia into mother sporocysts is induced, either in vivo by the penetration of the free-living larval stage, the miracidium, in the snail Biomphalaria glabrata or in vitro following the incubation of the miracidium in Chernin's Balanced Salt Solution (CBSS) or Bge (B. glabrata embryonic cell line) culture medium. The in vitro development of S. mansoni miracidium into mother sporocyst was monitored by Scanning Electron Microscopy (SEM) from 2.5 h to 120 h in CBSS. The transformation starts when the miracidium ciliate plates detach due to the proliferation of the intercellular ridge associated with the degeneration of mid-body papillae of the miracidium. The loss of ciliated plates causes the appearing of scars, filled across time by the proliferation of a new tegument originating from the interplate ridge. This new tegument covers the entire body of the metamorphosing parasite and differentiates over time, allowing some exchanges (uptakes or secretion/excretion) between the parasite and its host. In contrast to the well-described development of adult and free-living larval stages of S. mansoni using SEM, the developmental transformation of intramolluscan stages, especially tegumental changes in the mother sporocyst, has been sparcely documented at the ultrastructural level. In addition, taking into account the latest literature on miracidium electron microscopy and the advances in SEM technologies over the last thirty years, the present study gathers three main objectives: (i) Fill the gap of tegument scanning electron micrographs of in vitro transforming sporocysts; (ii) Update the current bibliographic miracidia and sporocysts image bank due to rapid evolution of SEM technology; (iii) Understand and describe the critical steps and duration of the in vitro miracidium-to-sporocyst transformation process to assist in understanding the interaction between the larval surface and snail immune factors.

Molecular detection of Schistosoma species in unusual snail hosts: a note of caution.

The interaction between snails and species of Schistosoma results from an evolutionary process with an intrinsic host-parasite specificity to the snail genus. Faced with this fact, the recent molecular-based report on the potential infection of the thiarid Melanoides tuberculata with human schistosome should be cautiously interpreted. The high sensibility of molecular tools can result in false positives, perhaps by amplifying DNA from an external (contaminant) or invasive stage of schistosome found in this non-permissive snail host. Thus, parasitological data are mandatory to extrapolate the importance of the finding for the epidemiology and control of schistosomiasis.

Biomphalaria straminea as an Intermediate Host of a Renal Trematode Species of the Genus Tanaisia (Trematoda: Eucotylidae) in Brazil.

PURPOSE: Eucotylid trematodes are parasites of the urinary system of birds with a cosmopolitan distribution. Despite the importance of these flukes, fundamental aspects of their biology, such as intermediate hosts and larval morphology, are poorly known. Herein, the potential involvement of aquatic mollusks in the transmission of a species of Tanaisia is reported for the first time. METHODS: During the search of non-emergent larval stages of trematodes in mollusks collected from an urban waterbody from Brazil in February of 2021, 1 out of 18 specimens (5.5%) of Biomphalaria straminea was found harboring sporocysts, cercariae and encysted metacercariae morphologically compatible with those described for eucotylid species. Sequences generated for 28S, ITS-2, and cox1 molecular markers were compared with sequences available in GenBank and subjected to phylogenetic analyses. RESULTS: Molecular analyses revealed parasite affiliation with members of the genus Tanaisia, given it groped in a strongly supported clade with species of this genus included in the 28S phylogenetic tree. The larvae tentatively identified as Tanaisia sp. can be conspecific with an unpublished isolate of Tanaisia valida found in birds in South Brazil (100% similarity in 28S and ITS-2). CONCLUSION: Biomphalaria straminea is reported as a natural host of a species of Tanaisia for the first time. This finding highlights the possibility, so far unknown, of transmission of species of the family Eucotylidae in aquatic environments.

From field to laboratory: isolation, genetic assessment, and parasitological behavior of Schistosoma mansoni obtained from naturally infected wild rodent Holochilus sciureus (Rodentia, Cricetidae), collected in Northeastern Brazil.

Wild rodent species are naturally infected by Schistosoma mansoni; however, the genetic characterization of the parasite, its parasitological features, and its role in human schistosomiasis are poorly understood. In this study, we isolated and characterized Schistosoma from naturally infected Holochilus sciureus, called HS strain, collected from a schistosomiasis endemic region in Maranhão State, Brazil. To isolate the parasite, miracidia obtained from the livers of H. sciureus were used to infect Biomphalaria glabrata of sympatric (called SB) and allopatric (called BH) strains, and the produced cercariae were subcutaneously inoculated into hamsters and/or BALB/c mice. Parasitological kinetics in experimentally infected hosts were evaluated, and the tRNACys-12S (referred to as 16S herein) and cox 1 regions of mtDNA from isolated worms were amplified and sequenced. Only miracidia obtained from infected mice, but not from hamsters, were capable of infecting B. glabrata, allowing maintenance of the isolated parasite. Cox1 and 16S mtDNA sequences showed 100% similarity with S. mansoni, and phylogenetic analysis showed that the HS strain of S. mansoni forms an assemblage with isolates from America and Kenya, confirming the conspecificity. Experimental infection of B. glabrata SB with S. mansoni HS resulted in two peaks of cercariae shedding at 45 and 70 days post-infection (dpi) and caused higher mortality than in B. glabrata BH. The worm recovery rate in mice was approximately 13%, and the peak of egg elimination occurred at the 10th week post-infection. Therefore, S. mansoni obtained from H. sciureus was successfully isolated, genetically characterized, and maintained in mice, allowing further study of this schistosome strain.

Experimental water hyacinth invasion and destructive management increase human schistosome transmission potential.

Invasive species cause environmental degradation, decrease biodiversity, and alter ecosystem function. Invasions can also drive changes in vector-borne and zoonotic diseases by altering important traits of wildlife hosts or disease vectors. Managing invasive species can restore biodiversity and ecosystem function, but it may have cascading effects on hosts, parasites, and human risk of infection. Water hyacinth, Eichhornia crassipes, is an extremely detrimental invader in many sites of human schistosome transmission, especially in Lake Victoria, where hyacinth is correlated with high snail abundance and hotspots of human schistosome infection. Hyacinth is often managed via removal or in situ destruction, but the effects of these strategies on snail intermediate hosts and schistosomes are not known. We evaluated the effects of water hyacinth invasion and these management strategies on the dynamics of human schistosomes, Schistosoma mansoni, and snails, Biomphalaria glabrata, in experimental mesocosms over 17 weeks. We hypothesized that hyacinth, which is inedible to snails, would affect snail growth, reproduction, and cercariae production through the balance of its competitive effects on edible algae and its production of edible detritus. We predicted that destruction would create a pulse of edible detrital resources, thereby increasing snail growth, reproduction, and parasite production. Conversely, we predicted that removal would have small or negligible effects on snails and schistosomes, because it would alleviate competition on edible algae without generating a resource pulse. We found that hyacinth invasion suppressed algae, changed the timing of peak snail abundance, and increased total production of human-infectious cercariae ~6-fold relative to uninvaded controls. Hyacinth management had complex effects on algae, snails, and schistosomes. Removal increased algal growth and snail abundance (but not biomass), and slightly reduced schistosome production. In contrast, destruction increased snail biomass (but not abundance), indicating increases in body size. Destruction caused the greatest schistosome production (10-fold more than the control), consistent with evidence that larger snails with greater access to food are most infectious. Our results highlight the dynamic effects of invasion and management on a globally impactful human parasite and its intermediate host. Ultimately, preventing or removing hyacinth invasions would simultaneously benefit human and environmental health outcomes.

Distribution and seasonal abundance of Biomphalaria snails and their infection status with Schistosoma mansoni in and around Lake Tana, northwest Ethiopia.

Biomphalaria snails, namely B. pfeifferi and B. sudanica, are the principal intermediate hosts for Schistosoma mansoni infection in Ethiopia. Epidemiological studies of Biomphalaria snails and their infection status with S. mansoni is vital for public health planning. This study aimed to assess the spatial and seasonal abundance of Biomphalaria snails as well as their infection status with S. mansoni around Lake Tana, northwest Ethiopia. Malacological survey was conducted from January 2021 to December 2021 in ten different collection sites in and around Lake Tana. Snail collection was performed for 20 min from each collection site seasonally (four times in a year) using a standard scoop and handpicking from aquatic vegetation. All collected snails were carefully examined based on their morphological features and all live Biomphalaria snails were subjected to cercariae shedding experiment. Descriptive statistics were used to determine the prevalence of S. mansoni infection and its relationship with snail collection sites and seasons. A total of 3886 freshwater snails were collected from ten collection sites around Lake Tana. Out of the total snails collected, 1606 (41.3%; 95% CI 39.77-42.89%) were Biomphalaria spp. The highest (374) and the lowest numbers (98) of Biomphalaria snails were collected from Shinne River and Qunzela Lakeshore, respectively. Out of the 1375 live Biomphalaria snails, 14.4% (95% CI 12.59-16.37%) snails shed cercariae, but only 4.87% (95% CI 3.79-6.15%) were cercariae of S. mansoni. The infection prevalence of S. mansoni ranged from 10.59% at the Cherechera site to 1.49% at Gumara River. Biomphalaria snail infections with S. mansoni cercariae were observed throughout the season, the highest and the lowest infection rates being in the spring and summer seasons. Significant differences in the prevalence of S. mansoni infection in Biomphalaria snails were observed across study sites and seasons (p < 0.05). Biomphalaria snails were the most abundant freshwater snails found in nearly all of snail collection sites throughout the year. It was revealed that nearly five percent of Biomphalaria snails were infected with S. mansoni cercariae. This study highlights the importance of appropriate snail control strategies to support the ongoing prevention and control of schistosomiasis around Lake Tana.

Single cell RNA sequencing reveals hemocyte heterogeneity in Biomphalaria glabrata: Plasticity over diversity.

The freshwater snail Biomphalaria glabrata is an intermediate host of Schistosoma mansoni, the agent of human intestinal schistosomiasis. However, much is to be discovered about its innate immune system that appears as a complex black box, in which the immune cells (called hemocytes) play a major role in both cellular and humoral response towards pathogens. Until now, hemocyte classification has been based exclusively on cell morphology and ultrastructural description and depending on the authors considered from 2 to 5 hemocyte populations have been described. In this study, we proposed to evaluate the hemocyte heterogeneity at the transcriptomic level. To accomplish this objective, we used single cell RNA sequencing (scRNAseq) technology coupled to a droplet-based system to separate hemocytes and analyze their transcriptome at a unique cell level in naive Biomphalaria glabrata snails. We were able to demonstrate the presence of 7 hemocyte transcriptomic populations defined by the expression of specific marker genes. As a result, scRNAseq approach showed a high heterogeneity within hemocytes, but provides a detailed description of the different hemocyte transcriptomic populations in B. glabrata supported by distinct cellular functions and lineage trajectory. As a main result, scRNAseq revealed the 3 main population as a super-group of hemocyte diversity but, on the contrary, a great hemocytes plasticity with a probable capacity of hemocytes to engage to different activation pathways. This work opens a new field of research to understand the role of hemocytes particularly in response to pathogens, and towards S. mansoni parasites.

Toxic, cytotoxic and genotoxic effect of plumbagin in the developmental stages of Biomphalaria glabrata (Say, 1818-intermediate host) and cercaricidal activity against the infectious agent of schistosomiasis mansoni.

BACKGROUND: Snails of the genus Biomphalaria are intermediate hosts of Schistosoma mansoni, the main etiological agent of schistosomiasis mansoni, which affects about 236.6 million people in tropical and subtropical regions of the world. The World Health Organization recommends the population control of vector snails as one of the strategies to reduce the prevalence and incidence of schistosomiasis. In this study, molluscicidal and antiparasitic activities of plumbagin, a naturally sourced naphthoquinone with a range of biological effects, were evaluated against B. glabrata and cercariae of S. mansoni. RESULTS: After 24 h of exposure, plumbagin demonstrated molluscicidal activity at low concentrations against embryos (LC50 of 0.56, 0.93, 0.68, 0.51 and 0.74 µg mL-1 for the blastula, gastrula, trochophore, veliger and hippo stage, respectively) and adult snails (LC50 of 3.56 µg mL-1 ). There were no changes in exposed snails' fecundity or fertility; however, plumbagin was able to increase the frequency of DNA damage and the number of hemocytes, with apoptosis and binucleation being the main hemocyte alterations. In addition, plumbagin showed death of S. mansoni cercariae in the concentration of 1.5 µg mL-1 in 60 min, while showing moderate toxicity to Artemia salina. CONCLUSION: Plumbagin proved to be a promising substance for the control of B. glabrata population, intermediate host of S. mansoni, as well as the cercariae, infective stage for humans (definitive host), while being moderately toxic to A. salina, a crustacean widely used in ecotoxicity tests. © 2022 Society of Chemical Industry.

Snail juvenile growth rate as a rapid predictor of the transmission potential of parasitizing human schistosomes.

Host and parasite traits that are sensitive to environmental perturbations merit special attention in the mitigation of diseases. While life table experiments allow a practical evaluation of variability of these traits with environmental change, they are cost and resource intensive. Here, we use a model snail host-trematode parasite system to test the efficacy of an expeditious alternative. Rapidly changing host traits (such as juvenile growth rate) can be used as effective predictors of parasite transmission potential across a range of environmental factors. This approach can be applied to anticipate epidemiological changes under diverse environmental scenarios.

Common aquatic pollutants modify hemocyte immune responses in Biomphalaria glabrata.

Disruptions to reproductive health in wildlife species inhabiting polluted environments is often found to occur alongside compromised immunity. However, research on impacts of aquatic pollution on freshwater mollusc immune responses is limited despite their importance as vectors of disease (Schistosomiasis) in humans, cattle and wild mammals. We developed an in vitro 'tool-kit' of well-characterized quantitative immune tests using Biomphalaria glabrata hemocytes. We exposed hemocytes to environmentally-relevant concentrations of common aquatic pollutants (17ß-estradiol, Bisphenol-A and p,p'-DDE) and measured key innate immune responses including motility, phagocytosis and encapsulation. Additionally, we tested an extract of a typical domestic tertiary treated effluent as representative of a 'real-world' mixture of chemicals. Encapsulation responses were stimulated by p,p'-DDE at low doses but were suppressed at higher doses. Concentrations of BPA (above 200 ng/L) and p,p'-DDE (above 500 ng/L) significantly inhibited phagocytosis compared to controls, whilst hemocyte motility was reduced by all test chemicals and the effluent extract in a dose-dependent manner. All responses occurred at chemical concentrations considered to be below the cytotoxic thresholds of hemocytes. This is the first time a suite of in vitro tests has been developed specifically in B. glabrata with the purpose of investigating the impacts of chemical pollutants and an effluent extract on immunity. Our findings indicate that common aquatic pollutants alter innate immune responses in B. glabrata, suggesting that pollutants may be a critical, yet overlooked, factor impacting disease by modulating the dynamics of parasite transmission between molluscs and humans.

Molecular characterization of thioester-containing proteins in Biomphalaria glabrata and their differential gene expression upon Schistosoma mansoni exposure.

Schistosomiasis is a disease caused by trematode parasites of the genus Schistosoma that affects approximately 200 million people worldwide. Schistosomiasis has been a persistent problem in endemic areas as there is no vaccine available, currently used anti-helmintic medications do not prevent reinfection, and most concerning, drug resistance has been documented in laboratory and field isolates. Thus, alternative approaches to curtail this human disease are warranted. Understanding the immunobiology of the obligate intermediate host of these parasites, which include the freshwater snail Biomphalaria glabrata, may facilitate the development of novel methods to stop or reduce transmission to humans. Molecules from the thioester-containing protein (TEP) superfamily have been shown to be involved in immunological functions in many animals including corals and humans. In this study we identified, characterized, and compared TEP transcripts and their expression upon S. mansoni exposure in resistant and susceptible strains of B. glabrata snails. Results showed the expression of 11 unique TEPs in B. glabrata snails. These transcripts present high sequence identity at the nucleotide and putative amino acid levels between susceptible and resistant strains. Further analysis revealed differences in several TEPs' constitutive expression levels between resistant and susceptible snail strains, with C3-1, C3-3, and CD109 having higher constitutive expression levels in the resistant (BS90) strain, whereas C3-2 and TEP-1 showed higher constitutive expression levels in the susceptible (NMRI) strain. Furthermore, TEP-specific response to S. mansoni miracidia exposure reiterated their differential expression, with resistant snails upregulating the expression of both TEP-4 and TEP-3 at 2 h and 48 h post-exposure, respectively. Further understanding the diverse TEP genes and their functions in invertebrate animal vectors will not only expand our knowledge in regard to this ancient family of immune proteins, but also offer the opportunity to identify novel molecular targets that could aid in the efforts to develop control methods to reduce schistosomiasis transmission.