The potential risk of Schistosoma mansoni transmission by the invasive freshwater snail Biomphalaria straminea in South China

The impact of ICOSL/ICOS pathway-regulated long non-coding RNAs on liver fibrosis in mice infected with Schistosoma japonicum

BACKGROUND

The primary pathogenic mechanism of schistosomiasis-associated liver fibrosis involves the deposition of schistosome eggs, leading to the formation of liver egg granulomas and subsequent liver fibrosis. Hepatic stellate cells are abnormally activated, resulting in excessive collagen deposition and fibrosis development. While specific long non-coding RNAs (lncRNAs) have been associated with fibrotic processes, their roles in schistosomiasis-associated liver fibrosis remain unclear.

METHODS

Our previous research indicated that downregulating the ICOSL/ICOS could partially alleviate liver fibrosis. In this study, we established a schistosomiasis infection model in C57BL/6 and ICOSL knockout (KO) mice, and the liver pathology changes were observed at various weeks postinfection (wpi) using hematoxylin and eosin and Masson's trichrome staining. Within the first 4 wpi, no significant liver abnormalities were observed. However, mice exhibited evident egg granulomas and fibrosis in their livers at 7 wpi. Notably, ICOSL-KO mice had significantly smaller pathological variations compared with simultaneously infected C57BL/6 mice. To investigate the impact of lncRNAs on schistosomiasis-associated liver fibrosis, quantitative real-time polymerase chain reaction (RT-qPCR) was used to monitor the dynamic changes of lncRNAs in hepatic stellate cells of infected mice.

RESULTS

The results demonstrated that lncRNA-H19, -MALAT1, -PVT1, -P21 and -GAS5 all participated in liver fibrosis formation after schistosome infection. In addition, ICOSL-KO mice exhibited significantly inhibited expression of lncRNA-H19, -MALAT1 and -PVT1 after 7 wpi. In contrast, they showed enhanced expression of lncRNA-P21 and -GAS5 compared with C57BL/6 mice, influencing liver fibrosis development. Furthermore, small interfering RNA transfection (siRNA) in JS-1 cells in vitro confirmed that lncRNA-H19, -MALAT1, and -PVT1 promoted liver fibrosis, whereas lncRNA-P21 and -GAS5 had the opposite effect on key fibrotic molecules, including α- smooth muscle actin and collagen I expression.

CONCLUSIONS

This study uncovers that ICOSL/ICOS may play a role in activating hepatic stellate cells and promoting liver fibrosis in mice infected with Schistosoma japonicum by dynamically regulating the expression of specific lncRNAs. These findings offer potential therapeutic targets for schistosomiasis-associated liver fibrosis.

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.

Snail microbiota and snail-schistosome interactions: axenic and gnotobiotic technologies

The microbiota in the intermediate snail hosts of human schistosomes can significantly affect host biology. For decades, researchers have developed axenic snails to manipulate the symbiotic microbiota. This review summarizes the characteristics of symbiotic microbes in intermediate snail hosts and describes their interactions with snails, affecting snail growth, development, and parasite transmission ability. We focus on advances in axenic and gnotobiotic technologies for studying snail-microbe interactions and exploring the role of microbiota in snail susceptibility to Schistosoma infection. We discuss the challenges related to axenic and gnotobiotic snails, possible solutions to address these challenges, and future research directions to deepen our understanding of snail-microbiota interactions, with the aim to develop microbiota-based strategies for controlling snail populations and reducing their competence in transmitting parasites.

Core gut microbes Cloacibacterium and Aeromonas associated with different gastropod species could be persistently transmitted across multiple generations

BACKGROUND

Studies on the gut microbiota of animals have largely focused on vertebrates. The transmission modes of commensal intestinal bacteria in mammals have been well studied. However, in gastropods, the relationship between gut microbiota and hosts is still poorly understood. To gain a better understanding of the composition of gut microbes and their transmission routes in gastropods, a large-scale and long-term experiment on the dynamics and transmission modes of gut microbiota was conducted on freshwater snails.

RESULTS

We analyzed 244 microbial samples from the digestive tracts of freshwater gastropods and identified Proteobacteria and Bacteroidetes as dominant gut microbes. Aeromonas, Cloacibacterium, and Cetobacterium were identified as core microbes in the guts, accounting for over 50% of the total sequences. Furthermore, both core bacteria Aeromonas and Cloacibacterium, were shared among 7 gastropod species and played an important role in determining the gut microbial community types of both wild and cultured gastropods. Analysis of the gut microbiota at the population level, including wild gastropods and their offspring, indicated that a proportion of gut microbes could be consistently vertically transmitted inheritance, while the majority of the gut microbes resulted from horizontal transmission. Comparing cultured snails to their wild counterparts, we observed an increasing trend in the proportion of shared microbes and a decreasing trend in the number of unique microbes among wild gastropods and their offspring reared in a cultured environment. Core gut microbes, Aeromonas and Cloacibacterium, remained persistent and dispersed from wild snails to their offspring across multiple generations. Interestingly, under cultured environments, the gut microbiota in wild gastropods could only be maintained for up to 2 generations before converging with that of cultured snails. The difference observed in gut bacterial metabolism functions was associated with this transition. Our study also demonstrated that the gut microbial compositions in gastropods are influenced by developmental stages and revealed the presence of Aeromonas and Cloacibacterium throughout the life cycle in gastropods. Based on the dynamics of core gut microbes, it may be possible to predict the health status of gastropods during their adaptation to new environments. Additionally, gut microbial metabolic functions were found to be associated with the adaptive evolution of gastropods from wild to cultured environments.

CONCLUSIONS

Our findings provide novel insights into the dynamic processes of gut microbiota colonization in gastropod mollusks and unveil the modes of microbial transmission within their guts. Video Abstract.

Chromosome-scale genome of the human blood fluke Schistosoma mekongi and its implications for public health

BACKGROUND

Schistosoma mekongi is a human blood fluke causing schistosomiasis that threatens approximately 1.5 million humans in the world. Nonetheless, the limited available S. mekongi genomic resources have hindered understanding of its biology and parasite-host interactions for disease management and pathogen control. The aim of our study was to integrate multiple technologies to construct a high-quality chromosome-level assembly of the S. mekongi genome.

METHODS

The reference genome for S. mekongi was generated through integrating Illumina, PacBio sequencing, 10 × Genomics linked-read sequencing, and high-throughput chromosome conformation capture (Hi-C) methods. In this study, we conducted de novo assembly, alignment, and gene prediction to assemble and annotate the genome. Comparative genomics allowed us to compare genomes across different species, shedding light on conserved regions and evolutionary relationships. Additionally, our transcriptomic analysis focused on genes associated with parasite-snail interactions in S. mekongi infection. We employed gene ontology (GO) enrichment analysis for functional annotation of these genes.

RESULTS

In the present study, the S. mekongi genome was both assembled into 8 pseudochromosomes with a length of 404 Mb, with contig N50 and scaffold N50 lengths of 1168 kb and 46,759 kb, respectively. We detected that 43% of the genome consists of repeat sequences and predicted 9103 protein-coding genes. We also focused on proteases, particularly leishmanolysin-like metalloproteases (M8), which are crucial in the invasion of hosts by 12 flatworm species. Through phylogenetic analysis, it was discovered that the M8 gene exhibits lineage-specific amplification among the genus Schistosoma. Lineage-specific expansion of M8 was observed in blood flukes. Additionally, the results of the RNA-seq revealed that a mass of genes related to metabolic and biosynthetic processes were up-regulated, which might be beneficial for cercaria production.

CONCLUSIONS

This study delivers a high-quality, chromosome-scale reference genome of S. mekongi, enhancing our understanding of the divergence and evolution of Schistosoma. The molecular research conducted here also plays a pivotal role in drug discovery and vaccine development. Furthermore, our work greatly advances the understanding of host-parasite interactions, providing crucial insights for schistosomiasis intervention strategies.

Gut microbiota in parasite-transmitting gastropods

BACKGROUND

Gastropoda, the largest class within the phylum Mollusca, houses diverse gut microbiota, and some gastropods serve as intermediate hosts for parasites. Studies have revealed that gut bacteria in gastropods are associated with various biological aspects, such as growth, immunity and host-parasite interactions. Here, we summarize our current knowledge of gastropod gut microbiomes and highlight future research priorities and perspectives.

METHODS

A literature search was undertaken using PubMed, Web of Science and CNKI for the articles on the gut microbiota of gastropods until December 31, 2022. We retrieved a total of 166 articles and identified 73 eligible articles for inclusion in this review based on the inclusion and exclusion criteria.

RESULTS

Our analysis encompassed freshwater, seawater and land snails, with a specific focus on parasite-transmitting gastropods. We found that most studies on gastropod gut microbiota have primarily utilized 16S rRNA gene sequencing to analyze microbial composition, rather than employing metagenomic, metatranscriptomic, or metabolomic approaches. This comprehensive review provided an overview of the parasites carried by snail species in the context of gut microbiota studies. We presented the gut microbial trends, a comprehensive summary of the diversity and composition, influencing factors, and potential functions of gastropod gut microbiota. Additionally, we discussed the potential applications, research gaps and future perspectives of gut microbiomes in parasite-transmitting gastropods. Furthermore, several strategies for enhancing our comprehension of gut microbiomes in snails were also discussed.

CONCLUSIONS

This review comprehensively summarizes the current knowledge on the composition, potential function, influencing factors, potential applications, limitations, and challenges of gut microbiomes in gastropods, with a specific emphasis on parasite-transmitting gastropods. These findings provide important insights for future studies aiming to understand the potential role of gastropod gut microbiota in controlling snail populations and snail-borne diseases.

Metagenomic Analysis Reveals Variations in Gut Microbiomes of the Schistosoma mansoni-Transmitting Snails Biomphalaria straminea and Biomphalaria glabrata

Biomphalaria snails play a crucial role in the transmission of the human blood fluke Schistosoma mansoni. The gut microbiota of intermediate hosts is known to influence their physiological functions, but little is known about its composition and role in Biomphalaria snails. To gain insights into the biological characteristics of these freshwater intermediate hosts, we conducted metagenomic sequencing on Biomphalaria straminea and B. glabrata to investigate variations in their gut microbiota. This study revealed that the dominant members of the gut microbiota in B. glabrata belong to the phyla Bacteroidetes and Proteobacteria, which were also found to be the top two most abundant gut bacteria in B. straminea. We identified Firmicutes, Acidovorax and Bosea as distinctive gut microbes in B. straminea, while Aeromonas, Cloacibacterium and Chryseobacterium were found to be dependent features of the B. glabrata gut microbiota. We observed significant differences in the community structures and bacterial functions of the gut microbiota between the two host species. Notably, we found a distinctive richness of antibiotic resistance genes (ARGs) associated with various classes of antibiotics, including bacitracin, chloramphenicol, tetracycline, sulfonamide, penicillin, cephalosporin_ii and cephalosporin_i, fluoroquinolone, aminoglycoside, beta-lactam, multidrug and trimethoprim, in the digestive tracts of the snails. Furthermore, this study revealed the potential correlations between snail gut microbiota and the infection rate of S. mansoni using Spearman correlation analysis. Through metagenomic analysis, our study provided new insights into the gut microbiota of Biomphalaria snails and how it is influenced by host species, thereby enhancing our understanding of variant patterns of gut microbial communities in intermediate hosts. Our findings may contribute to future studies on gastropod-microbe interactions and may provide valuable knowledge for developing snail control strategies to combat schistosomiasis in the future.

Status Quo and Future Perspectives of Molecular and Genomic Studies on the Genus Biomphalaria-The Intermediate Snail Host of Schistosoma mansoni

Schistosomiasis, or also generally known as bilharzia or snail fever, is a parasitic disease that is caused by trematode flatworms of the genus Schistosoma. It is considered by the World Health Organisation as the second most prevalent parasitic disease after malaria and affects more than 230 million people in over 70 countries. People are infected via a variety of activities ranging from agricultural, domestic, occupational to recreational activities, where the freshwater snails Biomphalaria release Schistosoma cercariae larvae that penetrate the skin of humans when exposed in water. Understanding the biology of the intermediate host snail Biomphalaria is thus important to reveal the potential spread of schistosomiasis. In this article, we present an overview of the latest molecular studies focused on the snail Biomphalaria, including its ecology, evolution, and immune response; and propose using genomics as a foundation to further understand and control this disease vector and thus the transmission of schistosomiasis.

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.

Potential Gut Microbiota Features for Non-Invasive Detection of Schistosomiasis

The gut microbiota has been identified as a predictive biomarker for various diseases. However, few studies focused on the diagnostic accuracy of gut microbiota derived-signature for predicting hepatic injuries in schistosomiasis. Here, we characterized the gut microbiomes from 94 human and mouse stool samples using 16S rRNA gene sequencing. The diversity and composition of gut microbiomes in Schistosoma japonicum infection-induced disease changed significantly. Gut microbes, such as Bacteroides, Blautia, Enterococcus, Alloprevotella, Parabacteroides and Mucispirillum, showed a significant correlation with the level of hepatic granuloma, fibrosis, hydroxyproline, ALT or AST in S. japonicum infection-induced disease. We identified a range of gut bacterial features to distinguish schistosomiasis from hepatic injuries using the random forest classifier model, LEfSe and STAMP analysis. Significant features Bacteroides, Blautia, and Enterococcus and their combinations have a robust predictive accuracy (AUC: from 0.8182 to 0.9639) for detecting liver injuries induced by S. japonicum infection in humans and mice. Our study revealed associations between gut microbiota features and physiopathology and serological shifts of schistosomiasis and provided preliminary evidence for novel gut microbiota-derived features for the non-invasive detection of schistosomiasis.

Bacillus subtilis Attenuates Hepatic and Intestinal Injuries and Modulates Gut Microbiota and Gene Expression Profiles in Mice Infected with Schistosoma japonicum

Parasitic infection can induce pathological injuries and impact the gut microbiota diversity and composition of the host. Bacillus subtilis is a nonpathogenic and noninvasive probiotic bacterium for humans and other animals, playing an important role in improving the host immune system’s ability to respond to intestinal and liver diseases and modulating gut microbiota. However, whether B. subtilis can impact biological functions in Schistosoma japonicum–infected mice is unclear. This study used oral administration (OA) of B. subtilis to treat mice infected with S. japonicum. We evaluated changes in the gut microbiota of infected mice using 16 S rRNA gene sequencing and differentially expressed gene profiles using transcriptome sequencing after OA B. subtilis. We found that OA B. subtilis significantly attenuated hepatic and intestinal pathological injuries in infected mice. The gut microbiota of mice were significantly altered after S. japonicum infection, while OA B. subtilis remodel the diversity and composition of gut microbiomes of infected mice. We found that the S. japonicum–infected mice with OA B. subtilis had an overabundance of the most prevalent bacterial genera, including Bacteroides, Enterococcus, Lactobacillus, Blautia, Lachnoclostridium, Ruminiclostridium, and Enterobacter. Transcriptomic analysis of intestinal tissues revealed that OA B. subtilis shaped the intestinal microenvironment of the host responding to S. japonicum infection. Differentially expressed genes were classified into KEGG pathways between S. japonicum–infected mice and those without included cell adhesion molecules, intestinal immune network for IgA production, hematopoietic cell lineage, Fc epsilon RI signaling pathway, Th1 and Th2 cell differentiation, Th17 cell differentiation, calcium signaling pathway, Fc gamma R-mediated phagocytosis, chemokine signaling pathway, phospholipase D signaling pathway, NF-kappa B signaling pathway, B cell receptor signaling pathway, pancreatic secretion, and phagosome. In conclusion, our findings showed that OA B. subtilis alleviates pathological injuries and regulates gene expression, implying that B. subtilis supplementation may be a potential therapeutic strategy for schistosomiasis. Our study may highlight the value of probiotics as a beneficial supplementary therapy during human schistosomiasis, but further studies are needed.

A proteomics evaluation of the primary and secondary immune response of Biomphalaria straminea challenged by Schistosoma mansoni

Biomphalaria spp. snails are intermediary hosts of Schistosoma mansoni, etiologic agent of intestinal schistosomiasis, one of the most important neglected tropical diseases. Biomphalaria straminea is an important intermediary host that possess a different phenotype to parasite infection but shows a large geographic distribution and high capacity of new ecologic niche invasion. Our purpose was to characterize for the first time the differentially expressed proteome in B. straminea during two times intervals after primary and secondary exposure to S. mansoni. The hemolymph was collected at 1 and 15 days after primary and secondary exposure of snails to the parasite. Total proteins were extracted and digested with trypsin. LC-MS/MS label-free quantification was performed and analyzed using Maxquant and Perseus software. Proteins were identified and annotated using Blast2GO tools. After 1 day of exposure, most of upregulated proteins are hemoglobin type 2, C and H type lectins, molecules related to cell adhesion, and response to oxidative stress. After 15 days, we found a similar pattern of upregulated proteins but some fibrinogen-related proteins (FREPs) and TEPs homologs were downregulated. Regarding the differentially expressed proteins during secondary response, the principal immune-related proteins upregulated were C and H type lectins, cellular adhesion molecules, biomphalysin, and FREP3. We noted a several upregulated biological processes during both responses that could be the one of the key points of efficacy in the immune response to parasite. Our data suggests different immune mechanisms used by B. straminea snails challenged with S. mansoni.

Molecular Characterization of Rotifers and Their Potential Use in the Biological Control of Biomphalaria

Background

Schistosomiasis is one of the most important tropical parasitic diseases worldwide. Biomphalaria straminea, the intermediate host of Schistosoma mansoni, has invaded and spread to Southern China since 1974 and may pose enormous threats to public health. Controlling intermediate host snails is an effective strategy in schistosomiasis intervention. However, the only effective chemical molluscicide, niclosamide, currently recommended by WHO may cause environmental pollution, loss of biodiversity, and high costs. Thus, to counter intermediate hosts, a sustainable and environmentally friendly tool is urgently needed. Here, we conducted field investigations to collect and identify a potential snail competitor rotifer and evaluated its molluscicide effect.

Results

In this study, we collected two samples of rotifers from Shenzhen. We found both red and black phenotypic B. straminea snails at the sampling sites. We identified the rotifer population as a species of the genus Philodina according to the amplification and phylogenetic analysis results of coxI gene. We found that rotifer exposure did not significantly affect the hatching rate of B. straminea eggs but promoted the killing of juvenile snails. Meanwhile, rotifer exposure did not significantly alter the fecundity of B. straminea quantified by the number of eggs per egg mass, the number of egg masses per snail, and the number of eggs per snail; but the snails exposed to rotifers showed lower fecundity performance than the control snails. Importantly, rotifer exposure could significantly affect the development of juvenile B. straminea, showing a smaller shell diameter of the exposed snails than that of the control snails. In addition, rotifer exposure affected the life span of B. straminea snails, showing a 16.61% decline in the average life span. After rotifer exposure, the S. mansoni-infected B. straminea snails died significantly faster than those without rotifer exposure. Similar findings were observed in S. mansoni-infected Biomphalaria glabrata snails. These results implied that rotifer exposure significantly promoted the mortality of S. mansoni-infected B. straminea and B. glabrata.

Conclusions

Our study demonstrated the potential molluscicide effect of rotifers on intermediate hosts under laboratory conditions. Our findings may provide new insights into the development of biocontrol strategies for snail-borne disease transmission.