Intermediate and definitive hosts of wild Schistosoma mansoni: ecological niche modeling of hosts in low endemicity areas.

The relationship between the environment and animal life began to be seen as an important tool to help control zoonoses. Climate variations lead to changes in the environment, which can influence the spatial distribution of species and, consequently, the spread of diseases to humans. Considered the main non-human definitive host species of Schistosoma mansoni in Brazil, the wild rodent Nectomys squamipes plays an important role as a reservoir in maintaining the schistosomiasis cycle in the absence of humans. This study demonstrates the results of ecological niche modeling of intermediate and definitive wild hosts of S. mansoni in the Regional Health Superintendence of Barbacena (Minas Gerais State), which has registered 31 municipalities, 80% of which are classified as endemic for parasitosis. Environmental variables associated with the distribution of each species were used based on information from the scientific collections of Global Biodiversity Information Facility (GBIF) and Species Link to project the ecological niche model in the geographic space. Abiotic variables such as the mean annual temperature, isothermality, and precipitation seasonality were obtained from World Clim. Ecological niche modeling of the wild host, N. squamipes, revealed the occurrence of the species in geographic overlap with the Biomphalaria species. Knowing the influence of bioclimatic variables and identifying favorable conditions for the establishment, occurrence, and distribution of species are important information for developing strategic actions for the surveillance and control of this endemic species. The presence of the definitive wild host needs to be considered by control programs of schistosomiasis.

Prevalence and correlations of schistosomiasis mansoni and schistosomiasis haematobium among humans and intermediate snail hosts: a systematic review and meta-analysis.

BACKGROUND: The control of schistosomiasis is particularly difficult in sub-Saharan Africa, which currently harbours 95% of this disease. The target population for preventive chemotherapy (PC) is expanded to all age group at risk of infection, thus increasing the demands of praziquantel (PZQ) tablets according to the new released guideline by World Health Organization. Due to the gap between available PZQ for PC and requirements, alternative approaches to assess endemicity of schistosomiasis in a community, are urgently needed for more quick and precise methods. We aimed to find out to which degree the infection status of snails can be used to guide chemotherapy against schistosomiasis. METHODS: We searched literature published from January 1991 to December 2022, that reported on the prevalence rates of Schistosoma mansoni, S. haematobium in the intermediate snails Biomphalaria spp. and Bulinus spp., respectively, and in humans. A random effect model for meta-analyses was used to calculate the pooled prevalence estimate (PPE), with heterogeneity assessed using I-squared statistic (I2), with correlation and regression analysis for the exploration of the relationship between human S. mansoni and S. haematobium infections and that in their specific intermediate hosts. RESULTS: Forty-seven publications comprising 59 field investigations were included. The pooled PPE of schistosomiasis, schistosomiasis mansoni and schistosomiasis haematobium in humans were 27.5% [95% confidence interval (CI): 24.0-31.1%], 25.6% (95% CI: 19.9-31.3%), and 28.8% (95% CI: 23.4-34.3%), respectively. The snails showed an overall infection rate of 8.6% (95% CI: 7.7-9.4%), with 12.1% (95% CI: 9.9-14.2%) in the Biomphalaria spp. snails and 6.9% (95% CI: 5.7-8.1%) in the Bulinus spp. snails. The correlation coefficient was 0.3 (95% CI: 0.01-0.5%, P < 0.05) indicating that the two variables, i.e. all intermediate host snails on the one hand and the human host on the other, were positively correlated. CONCLUSIONS: The prevalence rate of S. mansoni and S. haematobium is still high in endemic areas. Given the significant, positive correlation between the prevalence of schistosomes in humans and the intermediate snail hosts, more attention should be paid to programme integration of snail surveillance in future.

ARGONAUTE2 Localizes to Sites of Sporocysts in the Schistosome-Infected Snail, Biomphalaria glabrata.

MicroRNAs (miRNAs) are a class of small regulatory RNA that are generated via core protein machinery. The miRNAs direct gene-silencing mechanisms to mediate an essential role in gene expression regulation. In mollusks, miRNAs have been demonstrated to be required to regulate gene expression in various biological processes, including normal development, immune responses, reproduction, and stress adaptation. In this study, we aimed to establishment the requirement of the miRNA pathway as part of the molecular response of exposure of Biomphalaria glabrata (snail host) to Schistosoma mansoni (trematode parasite). Initially, the core pieces of miRNA pathway protein machinery, i.e., Drosha, DGCR8, Exportin-5, Ran, and Dicer, together with the central RNA-induced silencing complex (RISC) effector protein Argonaute2 (Ago2) were elucidated from the B. glabrata genome. Following exposure of B. glabrata to S. mansoni miracidia, we identified significant expression up-regulation of all identified pieces of miRNA pathway protein machinery, except for Exportin-5, at 16 h post exposure. For Ago2, we went on to show that the Bgl-Ago2 protein was localized to regions surrounding the sporocysts in the digestive gland of infected snails 20 days post parasite exposure. In addition to documenting elevated miRNA pathway protein machinery expression at the early post-exposure time point, a total of 13 known B. glabrata miRNAs were significantly differentially expressed. Of these thirteen B. glabrata miRNAs responsive to S. mansoni miracidia exposure, five were significantly reduced in their abundance, and correspondingly, these five miRNAs were determined to putatively target six genes with significantly elevated expression and that have been previously associated with immune responses in other animal species, including humans. In conclusion, this study demonstrates the central importance of a functional miRNA pathway in snails, which potentially forms a critical component of the immune response of snails to parasite exposure. Further, the data reported in this study provide additional evidence of the complexity of the molecular response of B. glabrata to S. mansoni infection: a molecular response that could be targeted in the future to overcome parasite infection and, in turn, human schistosomiasis.

Breaking Biomphalaria black box by in situ revelation of fluorescent Schistosoma mansoni parasites.

Tissue clearing is an old-fashioned method developed in the 1900's and used to turn an opaque biological object into a 3D visualizable transparent structure. Developed and diversified over the last decade, this method is most of the time applied to mammals' tissues, and especially mouse and human tissues for cytological, histological and pathophysiological studies. Through autofluorescence, immunofluorescence, in situ hybridization, intercalating agents, fluorescent transfection markers or fluorescent particle uptake, optically cleared samples can be monitored to discover new biological structures and cellular interactions through 3D-visualization, which can be more challenging in some extend through classical histological methods. Most of the tissue clearing procedures have been developed for specific applications like endogenous fluorescence visualization, immunolabeling or for revealing specific organs. Thus, choosing the adapted protocol may be empirical for non-model species, especially for mollusks for which very little related literature is available. Herein, we suggest an effective optical tissue clearing procedure for the freshwater snail Biomphalaria glabrata, known as the intermediate host of the human parasite Schistosoma mansoni. This clearing procedure involves solvents with a minimal toxicity, preserves the endogenous fluorescence of labeled parasites inside snail tissues and is compatible with an immunolabeling procedure.

[Molecular tracing of Biomphalaria straminea in China].

OBJECTIVE: To investigate the origin of Biomphalaria straminea in China, so as to provide insights into assessment of schistosomiasis mansoni transmission risk and B. straminea control. METHODS: Guanlan River, Dasha River, Shenzhen Reservoir, upper and lower reaches of Kuiyong River, and Xinzhen River in Shenzhen, China, were selected as sampling sites. Ten Biomphalaria samples were collected from each site, and genomic DNA was extracted from Biomphalaria samples. DNA samples were obtained from 15 B. straminea sampled from 5 sampling sites in Minas Gerais State, Pará State, Federal District, Pernambuco State, and Sao Paulo State in Brazil, South America. Cytochrome c oxidase I (COI) and mitochondrial 16S ribosomal RNA (16S rRNA) genes were sampled using the above DNA templates, and the amplified products were sequenced. The COI and 16S rRNA gene sequences were downloaded from GenBank, and the sampling sites were acquired. All COI and 16S rRNA gene sequences were aligned and evolutionary trees of B. straminea were created based on COI and 16S rRNA gene sequences to identify the genetic similarity and evolutionary relationship between B. straminea samples from China and South America. RESULTS: A total of 60 COI gene sequences with a length of 529 bp and 3 haplotypes were obtained from B. straminea sampled from China. There were 165 COI gene sequences of B. straminea retrieved from GenBank, and following alignment with the above 60 gene sequences, a total of 33 haplotypes were obtained. Phylogenetic analysis showed that the three haplotypes of B. straminea from China were clustered into one clade, among which the haplotype China11 and three B. straminea samples from Brazil retrieved from GenBank belonged to the same haplotype. Geographical evolution analysis showed that the B. straminea samples from three sampling sites along eastern coasts of Brazil had the same haplotype with China11, and B. straminea samples from other two sampling sites were closely, genetically related to China11. A total of 60 16S rDNA gene sequences with approximately 322 bp in length were amplified from B. straminea in China, with 2 haplotypes identified. A total of 70 16S rDNA gene sequences of B. straminea were captured from GenBank. Phylogenetic analysis showed that Biomphalaria snails collected from China were clustered into a clade, and the haplotype China64 and the haplotype 229BS from Brazil shared the same haplotype. The 49 16S rDNA gene sequences of B. straminea from 25 sampling sites in southern Brazil, which were captured from GenBank, were included in the present analysis, and the B. straminea from 3 sampling sites shared the same haplotype with China64 in China. Geographical evolution analysis based on COI and 16S rRNA gene sequences showed that B. straminea sampled from eastern coastal areas of Brazil shared the same haplotypes in two gene fragment sequences with Biomphalaria snails collected from China. CONCLUSIONS: The Biomphalaria snails in China are characterized as B. straminea, which have a low genetic diversity. The Biomphalaria snails in China have a high genetic similarity with B. straminea sampled from eastern coastal areas of Brazil, which may have originated from the eastern coastal areas of Brazil.

Metabolic disruptions in Biomphalaria glabrata induced by Heterorhabditis bacteriophora HP88: Implications for entomopathogenic nematodes in biological control.

Research on the use of entomopathogenic nematodes (EPNs) as a potential tool for the biological control of invertebrates has been growing in recent years, including studies involving snails with One Health importance. In this study, the effect of exposure time (24 or 48 h) of Heterorhabditis bacteriophora HP88 on the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), as well as the concentration of total proteins, uric acid, and urea in the hemolymph of Biomphalaria glabrata, were investigated. The concentrations of these metabolic markers were measured weekly until the end of the third week after exposure. Along with a significant reduction in total protein levels, a significant increase (p < 0.01) in uric acid and urea contents in the hemolymph of B. glabrata exposed to H. bacteriophora was observed. The accumulation of urea in these mollusks could lead to deleterious effects due to its high toxicity, inducing significant cell damage. Variations in transaminase activities were also observed, with snails exposed to EPNs showing significantly higher values (p < 0.01) than individuals in the control group, both for ALT and AST. These results indicate that experimental exposure to infective juveniles of H. bacteriophora causes significant alterations in the metabolic pattern of B. glabrata, compromising the maintenance of its homeostasis. Finally, exposure for 48 h caused more damage to the planorbid in question compared to snails exposed for 24 h, suggesting that the exposure time may influence the intensity of the host's response.

Climate and urbanization drive changes in the habitat suitability of Schistosoma mansoni competent snails in Brazil.

Schistosomiasis is a neglected tropical disease caused by Schistosoma parasites. Schistosoma are obligate parasites of freshwater Biomphalaria and Bulinus snails, thus controlling snail populations is critical to reducing transmission risk. As snails are sensitive to environmental conditions, we expect their distribution is significantly impacted by global change. Here, we used machine learning, remote sensing, and 30 years of snail occurrence records to map the historical and current distribution of forward-transmitting Biomphalaria hosts throughout Brazil. We identified key features influencing the distribution of suitable habitat and determined how Biomphalaria habitat has changed with climate and urbanization over the last three decades. Our models show that climate change has driven broad shifts in snail host range, whereas expansion of urban and peri-urban areas has driven localized increases in habitat suitability. Elucidating change in Biomphalaria distribution-while accounting for non-linearities that are difficult to detect from local case studies-can help inform schistosomiasis control strategies.

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi.

BACKGROUND: Along the southern shoreline of Lake Malawi, the incidence of schistosomiasis is increasing with snails of the genera Bulinus and Biomphalaria transmitting urogenital and intestinal schistosomiasis, respectively. Since the underlying distribution of snails is partially known, often being focal, developing pragmatic spatial models that interpolate snail information across under-sampled regions is required to understand and assess current and future risk of schistosomiasis. METHODS: A secondary geospatial analysis of recently collected malacological and environmental survey data was undertaken. Using a Bayesian Poisson latent Gaussian process model, abundance data were fitted for Bulinus and Biomphalaria. Interpolating the abundance of snails along the shoreline (given their relative distance along the shoreline) was achieved by smoothing, using extracted environmental rainfall, land surface temperature (LST), evapotranspiration, normalised difference vegetation index (NDVI) and soil type covariate data for all predicted locations. Our adopted model used a combination of two-dimensional (2D) and one dimensional (1D) mapping. RESULTS: A significant association between normalised difference vegetation index (NDVI) and abundance of Bulinus spp. was detected (log risk ratio - 0.83, 95% CrI - 1.57, - 0.09). A qualitatively similar association was found between NDVI and Biomphalaria sp. but was not statistically significant (log risk ratio - 1.42, 95% CrI - 3.09, 0.10). Analyses of all other environmental data were considered non-significant. CONCLUSIONS: The spatial range in which interpolation of snail distributions is possible appears < 10km owing to fine-scale biotic and abiotic heterogeneities. The forthcoming challenge is to refine geospatial sampling frameworks with future opportunities to map schistosomiasis within actual or predicted snail distributions. In so doing, this would better reveal local environmental transmission possibilities.

Mapping of intermediate host snails for schistosomiasis in the Democratic Republic of Congo: a systematic review.

Schistosomiasis is a snail-borne disease that has a considerable impact on human and animal health, particularly in sub-Saharan Africa. The intermediate hosts of the schistosome parasites are freshwater snails of the genera Biomphalaria Preston, 1910 and Bulinus Müller, 1781. In order to identify existing gaps in the spread of the disease in the Democratic Republic of Congo (DRC), this study compiled the available knowledge of the distribution, population dynamics and ecology of the intermediate hosts of schistosomiasis. A systematic literature search was conducted in PubMed, Embase and Scopus for all malacological studies on schistosoma intermediate hosts in DRC published between 1927 and October 2022. A total of 55 records were found, of which 31 met the inclusion criteria: these were published field and experimental studies conducted in the DRC and focused on snails as intermediate hosts of schistosomes. The analysis of these studies revealed that more up-to-date data on the distribution of snail intermediate hosts in the DRC are needed. Moreover, ecological factors have been less studied for Bulinus species than for Biomphalaria species. These factors play a crucial role in determining suitable snail habitats, and the lack of comprehensive information poses a challenge in snail control. This review makes it clear that there are no current malacological data in the DRC. There is a clear need for molecular and ecological research to update the exact species status and population dynamics of all potential intermediate host species. This will facilitate targeted snail control measures that complement drug treatment in the control of schistosomiasis in the country.

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.

Re-assessing thermal response of schistosomiasis transmission risk: Evidence for a higher thermal optimum than previously predicted.

The geographical range of schistosomiasis is affected by the ecology of schistosome parasites and their obligate host snails, including their response to temperature. Previous models predicted schistosomiasis' thermal optimum at 21.7°C, which is not compatible with the temperature in sub-Saharan Africa (SSA) regions where schistosomiasis is hyperendemic. We performed an extensive literature search for empirical data on the effect of temperature on physiological and epidemiological parameters regulating the free-living stages of S. mansoni and S. haematobium and their obligate host snails, i.e., Biomphalaria spp. and Bulinus spp., respectively. We derived nonlinear thermal responses fitted on these data to parameterize a mechanistic, process-based model of schistosomiasis. We then re-cast the basic reproduction number and the prevalence of schistosome infection as functions of temperature. We found that the thermal optima for transmission of S. mansoni and S. haematobium range between 23.1-27.3°C and 23.6-27.9°C (95% CI) respectively. We also found that the thermal optimum shifts toward higher temperatures as the human water contact rate increases with temperature. Our findings align with an extensive dataset of schistosomiasis prevalence in SSA. The refined nonlinear thermal-response model developed here suggests a more suitable current climate and a greater risk of increased transmission with future warming for more than half of the schistosomiasis suitable regions with mean annual temperature below the thermal optimum.

Citizens can help to map putative transmission sites for snail-borne diseases.

INTRODUCTION: Schistosomiasis and fasciolosis are snail-borne diseases of great medical and veterinary health importance. The World Health Organization recommends complementing drug treatment with snail control and community involvement for disease elimination, but there is a general lack of snail experts and hence snail distribution data. Therefore, we adopted a citizen science approach and involved citizens in the monitoring of medically and veterinary important snail taxa. MATERIALS AND METHODS: Snail data was collected weekly by 25 trained citizen scientists (CSs) at 76 sites around southern Lake Albert (Uganda) for 20 months. At each site, snails were searched for 30 minutes, sorted, target snail hosts identified to genus level, counted and data submitted through a smartphone application. The quality of this data was assessed by comparing it to monthly data collected by an 'expert' malacologist using the same sampling protocol. Generalised binomial logistic and linear mixed-effects models were used to analyse the variables for agreement between the CSs and expert. FINDINGS: The binary agreement in presence/absence of Biomphalaria, Bulinus and Radix snails reported by the expert and CSs ranged between 70% and 86% (900 reports) with an average of 17% false negatives (sites wrongly defined as snail-free). The agreement for Biomphalaria and Radix increased with snail abundance, and false negatives decreased when the number of snails collected by citizens was aggregated per month. Site type significantly predicted binary agreement, which was lowest at lake sites (55%) and highest at spring sites (99%) with variations across genera. Similar temporal trends in snail abundance were recorded despite the expert reporting higher abundance. However, the relative abundance was consistent across site types. The match between the sites with highest Biomphalaria spp. abundance identified by CSs and expert was consistently high (~84.1%) and increased over time. CONCLUSIONS AND RECOMMENDATIONS: Our results demonstrate the potential of citizen science to map putative schistosomiasis transmission sites. We therefore argue that this inclusive, powerful and cost-effective approach can be more sustainable than top-down monitoring and intervention campaigns.

Biological, biochemical and genotoxicological alterations of Benzylamine on Biomphalaria alexandrina snails and its Schistosoma mansoni larvicidal potential.

Biomphalaria spp. snails are freshwater gastropods that responsible for Schistosoma mansoni transmission. Schistosomiasis is a chronic illness that occurred in underdeveloped regions with poor sanitation. The aim of the present study is to evaluate the molluscicidal activity of benzylamine against B. alexandrina snails and it larvicidal effects on the free larval stages of S. mansoni. Results showed that benzylamine has molluscicidal activity against adult B. alexandrina snails after 24 h of exposure with median lethal concentration (LC50) 85.7 mg/L. The present results indicated the exposure of B. alexandrina snails to LC10 or LC25 of benzylamine resulted in significant decreases in the survival, fecundity (eggs/snail/week) and reproductive rates, acetylcholinesterase, albumin, protein, uric acid and creatinine concentrations, levels of Testosterone (T) and 17ß Estradiol (E), while alkaline phosphatase levels were significantly increased in comparison with control ones. The present results showed that the sub lethal concentration LC50 (85.7 mg/L) of benzylamine has miracidial and cercaricidal activities, where the Lethal Time (LT50) for miracidiae was 17.08 min while for cercariae was 30.6 min. Also, results showed that were decreased significantly after exposure to sub lethal concentrations compared with control. The present results showed that the expression level of NADH dehydrogenase subunit 1 (ND1) genes and cytochrome oxidase subunit I (COI) in B. alexandrina snails exposed to LC10 or LC25 concentrations benzylamine were significantly decreased compared to the control groups. Therefore, benzylamine could be used as effective molluscicide to control schistosomiasis.

Impact of environmental factors on Biomphalaria pfeifferi vector capacity leading to human infection by Schistosoma mansoni in two regions of western Côte d'Ivoire.

ABSTRACT: BACKGROUND: Intestinal schistosomiasis remains a worrying health problem, particularly in western Côte d'Ivoire, despite control efforts. It is therefore necessary to understand all the factors involved in the development of the disease, including biotic and abiotic factors. The aim of this study was to examine the factors that could support the maintenance of the intermediate host and its vectorial capacity in western Côte d'Ivoire. METHODS: Data on river physicochemical, microbiological, and climatic parameters, the presence or absence of snails with Schistosoma mansoni, and human infections were collected between January 2020 and February 2021. Spearman rank correlation tests, Mann-Whitney, analysis of variance (ANOVA), and an appropriate model selection procedure were used to analyze the data. RESULTS: The overall prevalence of infected snails was 56.05%, with infection reaching 100% in some collection sites and localities. Of 26 sites examined, 25 contained thermophilic coliforms and 22 contained Escherichia coli. Biomphalaria pfeifferi was observed in environments with lower land surface temperature (LST) and higher relative air humidity (RAH), and B. pfeifferi infection predominated in more acidic environments. Thermal coliforms and E. coli preferred higher pH levels. Lower maximum LST (LST_Max) and higher RAH and minimum LST (LST_Min) were favorable to E. coli, and lower LST_Max favored coliforms. The presence of B. pfeifferi was positively influenced by water temperature (T °C), LST_Min, RAH, and precipitation (Pp) (P < 0.05) and negatively influenced by pH, total dissolved solids (TDS), electrical conductivity (EC), LST_Max, and mean land surface temperature (LST). The parameters pH, TDS, EC, LST_Min, LST, and Pp had a positive impact on snail infection, while LST_Max had a negative impact on infection. Only pH had a positive effect on coliform and E. coli abundance. Of the 701 people examined for human schistosomiasis, 73.13% were positive for the point-of-care circulating cathodic antigen (POC-CCA) test and 12.01% for the Kato-Katz (KK) test. A positive correlation was established between human infections and the abundance of Biomphalaria (r2 = 0.879, P = 0.04959). CONCLUSIONS: The results obtained reflect the environmental conditions that are conducive to the maintenance of S. mansoni infection in this part of the country. To combat this infection as effectively as possible, it will be necessary not only to redouble efforts but also to prioritize control according to the level of endemicity at the village level.

Combining a transcriptomic approach and a targeted metabolomics approach for deciphering the molecular bases of compatibility phenotype in the snail Biomphalaria glabrata toward Schistosoma mansoni.

Biomphalaria glabrata is a freshwater snail and the obligatory intermediate host of Schistosoma mansoni parasite, the etiologic agent of intestinal Schistosomiasis, in South America and Caribbean. Interestingly in such host-parasite interactions, compatibility varies between populations, strains or individuals. This observed compatibility polymorphism is based on a complex molecular-matching-phenotype, the molecular bases of which have been investigated in numerous studies, notably by comparing between different strains or geographical isolates or clonal selected snail lines. Herein we propose to decipher the constitutive molecular support of this interaction in selected non-clonal resistant and susceptible snail strain originating from the same natural population from Brazil and thus having the same genetic background. Thanks to a global RNAseq transcriptomic approach on whole snail, we identified a total of 328 differentially expressed genes between resistant and susceptible phenotypes among which 129 were up-regulated and 199 down-regulated. Metabolomic studies were used to corroborate the RNAseq results. The activation of immune genes and specific metabolic pathways in resistant snails might provide them with the capacity to better respond to parasite infection.

Green synthesis of silver nanoparticles using Croton urucurana and their toxicity in freshwater snail species Biomphalaria glabrata.

Green silver nanoparticles (G-Ag NPs) have contributed to the development of ecological technologies with low environmental impact and safer for human health, as well as demonstrating potential for the control of vectors and intermediate hosts. However, knowledge about its toxicity in the early stages of gastropod development remains scarce. Therefore, the current study aimed to investigate the toxicity of G-Ag NPs synthesized from Croton urucurana leaf extracts in snail species Biomphalaria glabrata, which is an intermediate host for Schistosoma mansoni parasite. G-Ag NPs were synthesized using two types of plant extracts (aqueous and hydroethanolic) and characterized using multiple techniques. Bioassays focused on investigating G-Ag NPs and plant extracts were carried out with embryos and newly hatched snails, for 144 h and 96 h, respectively; toxicity was analyzed based on mortality, hatching, development inhibition, and morphological changes. Results have shown that both G-Ag NPs were more toxic to embryos and newly hatched snails than the investigated plant extracts. G-Ag NPs deriving from aqueous extract have higher molluscicidal activity than those deriving from hydroethanolic extract. Both G-Ag NPs induced mortality, hatching delay, development inhibition, and morphological changes (i.e., hydropic embryos), indicating their molluscicidal activities. Moreover, embryos were more sensitive to G-Ag NPs than newly hatched snails. Thus, the toxicity of G-Ag NPs to freshwater snails depends on the type of extracts and the snail's developmental stages. These findings can contribute to the development of green nanobiotechnologies applicable to control snails of medical importance.

Multi-biomarker approach to evaluate the toxicity of chlorpyrifos (active ingredient and a commercial formulation) on different stages of Biomphalaria straminea.

Biomphalaria straminea is a freshwater gastropod native to South America and used in toxicological assessments. Our aim was to estimate 48 h-LC50 and sub-chronic effects after the exposure to low concentrations of chlorpyrifos as commercial formulation (CF) and active ingredient (AI) on B. straminea adult, embryos and juveniles. Concentrations between 1 and 5000 µg L-1 were chosen for acute exposures and 0.1 and 1 µg L-1 for the sub-chronic one. After 14 days biochemical parameters, viability and sub-populations of hemocytes, reproductive parameters, embryotoxicity and offspring' survival were studied. Egg masses laid between day 12 and 14 were separated to continue the exposure and the embryos were examined daily. Offspring' survival and morphological changes were registered for 14 days after hatching. 48 h-LC50, NOEC and LOEC were similar between CF and AI, however the CF caused more sub-lethal effects. CF but not the AI decreased carboxylesterases, catalase and the proportion of hyalinocytes with respect to the total hemocytes, and increased superoxide dismutase and the % of granulocytes with pseudopods. Also CF caused embryotoxicity probably due to the increase of embryos' membrane permeability. Acetylcholinesterase, superoxide dismutase, hemocytes sub-populations, the time and rate of hatching and juveniles' survival were the most sensitive biomarkers. We emphasize the importance of the assessment of a battery of biomarkers as a useful tool for toxicity studies including reproduction parameters and immunological responses. Also, we highlight the relevance of incorporating the evaluation of formulations in order to not underestimate the effects of pesticides on the environment.

Order and timing of infection with different parasite life stages impacts host and parasite life histories.

Co-exposure to multiple parasites can alter parasite success and host life history when compared to single infections. These infection outcomes can be affected by the order of parasite arrival, the host immune response, and the interspecific interactions among co-infecting parasites. In this study, we examined how the arrival order of two trematode parasites, Schistosoma mansoni and Echinostoma caproni, influenced parasite ecology and the life history of their snail host, Biomphalaria glabrata. Snail hosts were exposed to E. caproni cercariae before, with, and after their exposure to S. mansoni miracidia. We then measured the effects of this timing on infection prevalence, infection intensity of E. caproni metacercariae, and cercarial output of S. mansoni, as well as on snail reproduction and survival. Snails infected only with S. mansoni and snails exposed to E. caproni after S. mansoni both shed more cercariae than simultaneously exposed snails. Additionally, S. mansoni prevalence was lower in snails that were first exposed to E. caproni compared to snails that were exposed to E. caproni after S. mansoni. Moreover, snails exposed to E. caproni before S. mansoni did not differ in their survival compared to control snails, whereas simultaneously exposed snails and snails exposed to E. caproni after S. mansoni had lower survival than control snails. Combined, this prevalence and survival data suggest a potential protective role of early E. caproni exposure. The timing of E. caproni exposure impacts S. mansoni establishment and reproduction, but host survival patterns are likely driven by S. mansoni prevalence alone.

Activities of pumpkin seed oil against Biomphalaria alexandrina snails and the infective stages of Schistosoma mansoni with special emphasis on genotoxic and histopathological alterations.

Schistosomiasis is a serious health issue in tropical regions, and natural compounds have gained popularity in medical science. This study investigated the potential effects of pumpkin seed oil (PSO) on Biomphalaria [B.] alexandrina snails (Ehrenberg, 1831), Schistosoma [S.] mansoni (Sambon, 1907) miracidium, and cercariae. The chemical composition of PSO was determined using gas chromatography/mass spectrometry. A bioassay was performed to evaluate the effects of PSO on snails, miracidia, and cercariae. The results showed no significant mortality of B. alexandrina snails after exposure to PSO, but it caused morphological changes in their hemocytes at 1.0 mg/ml for 24 hours. PSO exhibited larvicidal activity against miracidia after 2 hours of exposure at a LC50 of 618.4 ppm. A significant increase in the mortality rate of miracidia was observed in a dose- and time-dependent manner, reaching a 100% death rate after 10 minutes at LC90 and 15 minutes at LC50 concentration. PSO also showed effective cercaricidal activity after 2 hours of exposure at a LC50 of 290.5 ppm. Histological examination revealed multiple pathological changes in the digestive and hermaphrodite glands. The PSO had genotoxic effects on snails, which exhibited a significant increase [p≤0.05] in comet parameters compared to the control. The findings suggest that PSO has potential as a molluscicide, miracidicide, and cercaricide, making it a possible alternative to traditional molluscicides in controlling schistosomiasis.

The unusual kinetics of lactate dehydrogenase of Schistosoma mansoni and their role in the rapid metabolic switch after penetration of the mammalian host.

Lactate dehydrogenase (LDH) from Schistosoma mansoni has peculiar properties for a eukaryotic LDH. Schistosomal LDH (SmLDH) isolated from schistosomes, and the recombinantly expressed protein, are strongly inhibited by ATP, which is neutralized by fructose-1,6-bisphosphate (FBP). In the conserved FBP/anion binding site we identified two residues in SmLDH (Val187 and Tyr190) that differ from the conserved residues in LDHs of other eukaryotes, but are identical to conserved residues in FBP-sensitive prokaryotic LDHs. Three-dimensional (3D) models were generated to compare the structure of SmLDH with other LDHs. These models indicated that residues Val187, and especially Tyr190, play a crucial role in the interaction of FBP with the anion pocket of SmLDH. These 3D models of SmLDH are also consistent with a competitive model of SmLDH inhibition in which ATP (inhibitor) and FBP (activator) compete for binding in a well-defined anion pocket. The model of bound ATP predicts a distortion of the nearby key catalytic residue His195, resulting in enzyme inhibition. To investigate a possible physiological role of this allosteric regulation of LDH in schistosomes we made a kinetic model in which the allosteric regulation of the glycolytic enzymes can be varied. The model showed that inhibition of LDH by ATP prevents fermentation to lactate in the free-living stages in water and ensures complete oxidation via the Krebs cycle of the endogenous glycogen reserves. This mechanism of allosteric inhibition by ATP prevents the untimely depletion of these glycogen reserves, the only fuel of the free-living cercariae. Neutralization by FBP of this ATP inhibition of LDH prevents accumulation of glycolytic intermediates when S. mansoni schistosomula are confronted with the sudden large increase in glucose availability upon penetration of the final host. It appears that the LDH of S. mansoni is special and well suited to deal with the variations in glucose availability the parasite encounters during its life cycle.