Transcriptional responses of Biomphalaria pfeifferi and Schistosoma mansoni following exposure to niclosamide, with evidence for a synergistic effect on snails following exposure to both stressors

Distribution of the schistosome intermediate snail host Biomphalaria pfeifferi in East Africa's river systems and the prevalence of Schistosoma mansoni infection

BACKGROUND

There is a need for current and more detailed information on the distribution of Biomphalaria pfeifferi snails in East Africa's river systems. B. pfeifferi is arguably the most important snail intermediate host in the transmission of schistosomiasis, a disease ranked second to malaria in terms of tropical diseases of public health importance.

METHODS

We assessed the occurrence and geographical distribution of B. pfeifferi snails in Kenya, Uganda and Tanzania. Maximum entropy modelling was used to predict the potential distribution of B. pfeifferi snails and malacological surveys were conducted guided by MaxEnt predictions and information from previous studies. Malacological surveys were conducted at a total of 172 sites, including streams, rivers, dams, irrigation schemes and springs over a 3-y period from 2018 to 2020, with geospatial, ecological and physicochemical information recorded for each site.

RESULTS

B. pfeifferi snails were found at 23 of the 172 sites and inhabited a variety of habitat types. Of the 23 sites where B. pfeifferi snails were found, 15 (65.2%) were streams, 3 rivers (13.04%), 2 dams (8.7%), 2 springs (8.7%) and 1 an irrigation scheme (4.35%). B. pfeifferi abundance showed a significant positive correlation with increasing water temperature and decreasing water depth. In Kenya, B. pfeifferi snails were found around the Lake Victoria basin, the Mwea irrigation scheme and in parts of the former Eastern Province of Kenya. In Uganda, B. pfeifferi snails were found in Jinja District, Ntoroko District and Soroti District. In Tanzania, B. pfeifferi snails were found in the Iringa, Tabora and Kigoma Regions. We observed moderate to high prevalence of Schistosoma mansoni infection, with S. mansoni-infected snails found at 11 of 23 sites and with an average prevalence of 24.9% at infected sites. In Kenya, S. mansoni-infected snails were found in the Lake Victoria basin (22.5% prevalence at infected sites) and the former Eastern Province (13.5% prevalence at infected sites). In Uganda, infected snails were found in Ntoroko District (100% infected) and Soroti District (20% infected). In Tanzania, infected snails were found in the Kigoma Region, with a prevalence of 10% at the infected site.

CONCLUSION

This information on the distribution of B. pfeifferi snails and S. mansoni infection in East Africa's river systems can aid in developing better prevention and control strategies for human schistosomiasis. Regular surveys of the river systems for snail intermediate hosts followed by molecular detection of schistosome infection could form a basis for the development of a prompt and cost-effective surveillance system for schistosomiasis in the region.

Exploring the genome-wide transcriptomic responses of Bulinus truncatus to Schistosoma haematobium infection: An important host-parasite system involved in the transmission of human urogenital schistosomiasis

Freshwater snails of the genus Bulinus are critical hosts for Schistosoma haematobium, the causative agent of urogenital schistosomiasis. Among the 37 recognized Bulinus species, B. truncatus is a key vector. Using RNA sequencing (RNAseq), we investigated the genome-wide transcriptional responses of B. truncatus to S. haematobium infection. Our findings suggest that snails employ a complex defense strategy against the parasites by up-regulating genes involved in immune response, stress reaction, structural integrity, metabolism, and detoxification. In response, schistosome parasites appear to manipulate the snail's defense system, as evidenced by the suppression of immune-related genes such as ficolin, peptidoglycan recognition protein, and C-type lectin domain-containing protein genes. The down-regulation of biomphalysin 9, compared to its function in Biomphalaria glabrata, indicates divergent immune strategies among snail hosts. Additionally, we compared transcriptome profiles between embryos and juveniles, providing insights into developmental processes. This study offers valuable genomic data for Bulinus snails, illuminating the molecular interactions between bulinids and schistosomes, and advancing our understanding of their developmental biology.

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.

An Overview of Transcriptional Responses of Schistosome-Susceptible (M line) or -Resistant (BS-90) Biomphalaria glabrata Exposed or Not to Schistosoma mansoni Infection

Background

We seek to provide a comprehensive overview of transcriptomics responses of immune-related features of the gastropod Biomphalaria glabrata (Bg) following exposure to Schistosoma mansoni (Sm), a trematode causing human schistosomiasis. Responses of schistosome-susceptible (M line, or SUS) and -resistant (BS-90, or RES) Bg strains were characterized following exposure to Sm for 0.5, 2, 8 or 40 days post-exposure (dpe).

Methods

RNA-Seq and differential expression analysis were undertaken on 56 snails from 14 groups. We considered 7 response categories: 1) constitutive resistance factors; 2) constitutive susceptibility factors; 3) generalized stress responses; 4) induced resistance factors; 5) resistance factors suppressed in SUS snails; 6) suppressed/manipulated factors in SUS snails; and 7) tolerance responses in SUS snails. We also undertook a gene co-expression network analysis. Results from prior studies identifying schistosome resistance/susceptibility factors were examined relative to our findings.

Results

A total of 792 million paired-end reads representing 91.2% of the estimated 31,985 genes in the Bg genome were detected and results for the 7 categories compiled and highlighted. For both RES and SUS snails, a single most supported network of genes with highly correlated expression was found.

Conclusions

1) Several constitutive differences in gene expression between SUS and RES snails were noted, the majority over-represented in RES; 2) There was little indication of a generalized stress response shared by SUS and RES snails at 0.5 or 2 dpe; 3) RES snails mounted a strong, multi-faceted response by 0.5 dpe that carried over to 2 dpe; 4) The most notable SUS responses were at 40 dpe, in snails shedding cercariae, when numerous features were either strongly down-regulated indicative of physiological distress or parasite manipulation, or up-regulated, suggestive of tolerance or survival-promoting effects; 5) Of 55 genes previously identified in genome wide mapping studies, 29 (52.7%) were responsive to Sm, as were many familiar resistance-associated genes (41.0%) identified by other means; 6) Both network analysis and remarkably specific patterns of expression of lectins and G protein-coupled receptors in categories 4, 6 and 7 were indicative of orchestrated responses of different suites of genes in SUS or RES snails following exposure to Sm.

Nuclear genome of Bulinus truncatus, an intermediate host of the carcinogenic human blood fluke Schistosoma haematobium

Some snails act as intermediate hosts (vectors) for parasitic flatworms (flukes) that cause neglected tropical diseases, such as schistosomiases. Schistosoma haematobium is a blood fluke that causes urogenital schistosomiasis and induces bladder cancer and increased risk of HIV infection. Understanding the molecular biology of the snail and its relationship with the parasite could guide development of an intervention approach that interrupts transmission. Here, we define the genome for a key intermediate host of S. haematobium-called Bulinus truncatus-and explore protein groups inferred to play an integral role in the snail's biology and its relationship with the schistosome parasite. Bu. truncatus shared many orthologous protein groups with Biomphalaria glabrata-the key snail vector for S. mansoni which causes hepatointestinal schistosomiasis in people. Conspicuous were expansions in signalling and membrane trafficking proteins, peptidases and their inhibitors as well as gene families linked to immune response regulation, such as a large repertoire of lectin-like molecules. This work provides a sound basis for further studies of snail-parasite interactions in the search for targets to block schistosomiasis transmission.

Clinical and epidemiological aspects of feline sporotrichosis caused by Sporothrix brasiliensis and in vitro antifungal susceptibility

Sporotrichosis is a subcutaneous mycosis resulting from the traumatic implantation of pathogenic Sporothrix species. In Brazil, zoonotic transmission plays an important role in the epidemiology of the disease, involving especially cats. The objective of this study was to isolate Sporothrix spp. from cats with signs of sporotrichosis, determining the causative species, clinical and epidemiological aspects, and the in vitro susceptibility profile of the isolates against antifungal drugs. From September 2017 to February 2019, 245 samples of lesions were collected from symptomatic cats in São José do Rio Preto, Brazil. Identification of the isolates was performed by morphophysiological parameters and species-specific polymerase chain reaction. The susceptibility profile of the isolates was determined for five drugs (amphotericin B, itraconazole, ketoconazole, potassium iodide and terbinafine), using the broth microdilution method. Clinical and epidemiological aspects were analyzed based on data contained on investigation forms filled by the veterinarians at moment of collection. Sporothrix spp. were isolated in 189 (77.2%) of the samples. Phenotypic and molecular analyses revealed S. brasiliensis as the only causative agent. In vitro susceptibility testing showed lower MIC values for terbinafine (MIC = 0.03-2 μg/ml), ketoconazole (MIC = 0.03-2 μg/ml), and itraconazole (MIC = 0.03-4 μg/ml). Most of the animals were male (73.5%), adults (96.3%), stray (53.5%), and uncastrated (69.8%). Our results show the expansion of the S. brasiliensis epidemic to an area nearly 840 km apart from the epicenter of the long-lasting outbreak of cat-transmitted sporotrichosis in Rio de Janeiro.

Bulinus truncatus transcriptome – a resource to enable molecular studies of snail and schistosome biology

Despite advances in high-throughput sequencing and bioinformatics, molecular investigations of snail intermediate hosts that transmit parasitic trematodes are scant. Here, we report the first transcriptome for Bulinus truncatus – a key intermediate host of Schistosoma haematobium – a blood fluke that causes urogenital schistosomiasis in humans. We assembled this transcriptome from short- and long-read RNA-sequence data. From this transcriptome, we predicted 12,998 proteins, 58% of which had orthologs in Biomphalaria glabrata – an intermediate host of Schistosoma mansoni – a blood fluke that causes hepato-intestinal schistosomiasis. We predicted that select protein groups are involved in signal transduction, cell growth and death, the immune system, environmental adaptation and/or the excretory/secretory system, suggesting roles in immune responses, pathogen defence and/or parasite-host interactions. The transcriptome of Bu. truncatus provides a useful resource to underpin future molecular investigations of this and related snail species, and its interactions with pathogens including S. haematobium. The present resource should enable comparative investigations of other molluscan hosts of socioeconomically important parasites in the future.

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First transcriptome to represent Bulinus truncatus – a snail intermediate host of Schistosoma haematobium.

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Select protein groups of Bu. truncatus are inferred to associate with innate immune responses against pathogens.

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Transcriptome provides a resource for future studies of parasite-host interactions and snail-host resistance to pathogens.