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Abstract Body

Despite ongoing control, schistosomiasis remains a public health problem in Malawi. At the southern end of Lake Malawi, Mangochi District, there have been significant changes in the epidemiology of schistosomiasis and ecology of freshwater snail hosts. In this presentation, I review progress made uncovering the burdens of male genital schistosomiasis, an unfolding outbreak of intestinal schistosomiasis and the detection of hybrid schistosomes.

Since November 2017 repeated human/snail surveys have taken place using a combination of parasitological, non-invasive imagery and molecular methods for infection detection and disease diagnosis. These include (non)standard egg-detection methods, use of portable ultrasonography and application of real-timePCR/DNA genotyping.

Male genital schistosomiasis in men, with or without HIV infection, can be common along the shoreline of the lake; some 10% present with schistosome eggs in semen and this prevalence increases to approximately 25% when real-time PCR detection methods are applied. Upon the initial unexpected finding of Biomphalaria pfeifferi within the lake, latter targetted surveys in local school children revealed upto 75% of children have intestinal schistosomiasis, alongside 25% with urogenital schistosomiasis. Hybrid schistosomes of Schistosoma haematobium-mattheei have been detected alongside a hitherto unknown species diveristy within local Bulinus africanus group snails.

The changing epidemiological patterns here in Malawi give a new setting to schistosome transmission cycles and need to devise better control strategies. In light of COVID-19 impacts, a good starting point is to increase frequencies of preventive chemotherapy and take a OneHealth approach.

Introduction

Discoveries made over the past ten years have provided evidences that invertebrate antiparasitic response may be primed in a sustainable manner, leading to the failure of a secondary encounter with the same pathogen. This phenomenon called “immune priming” or "innate immune memory" (IIM) was mainly phenomenological and the underlying molecular mechanisms remained to be investigated in invertebrate organisms.

Methods

In order to achieve this ambitious goal, we focused our investigations using state-of-the-art Omics approaches on the Lophotrochozoan snail, Biomphalaria glabrata, in which, IIM was recently reported.

Results

We demonstrated that IIM response in B. glabrata is associated to a shift from a cellular immune response towards a humoral immune response. We investigate the epigenetic and metabolomic supports of innate immune memory on whole snails and snail immune cells, the hemocytes. We demonstrated that following primary infection, a metabolic and epigenetic reprogramming occurred in snail hemocytes, resulting in a strong transcriptional shift following the challenge.

Conclusions

These results prompted us to revisit the artificial dichotomy between innate and memory immunity in invertebrate systems and led us to new questions related to: how memory of pathogen exposures could be recorded, stored and recalled in invertebrate immune systems?

Introduction

The Schistosoma lifecycle involves the miracidia infection of an intermediate molluscan host, such as Biomphalaria glabrata. Synthesising and dispersing attractants from B. glabrata is a possible avenue of minimising infections. B. glabrata attractiveness is known to be reduced following infection; however, it is unclear how infection duration affects attractiveness. Identifying proteins abundant in attractive SCW may reveal attractant candidates.

Methods

This study compared the excretory–secretory proteins (ESPs) and behavioural effects of snail conditioned water (SCW) from B. glabrata that were naïve or 16h-, 1 week-, 2 weeks- or 3 weeks- post-miracidia exposure (PME). Behavioural changes in S. mansoni miracidia following SCW exposure was observed with Milli-Q water as a negative control. ESPs were quantitatively identified from SCW using a label-free proteomic method using B. glabrata and S. mansoni protein databases. Protein-protein interaction analyses were based on domain-domain interactions of identified S. mansoni and B. glabrata ESPs.

Results

Similar attractant behaviour was induced by naïve and 3W-PME SCW, including increased miracidia circling and quantity. Therefore, Biomphalaria-specific ESPs exclusive to naïve SCW, and shared between naïve and 3W-PME SCW, were considered attractant candidates. A total of 21 attractant candidate proteins were identified, including acetylcholine-binding protein, calmodulin, biomphalysins and thioester-containing protein.

Conclusions

This suggests that compromised production of specific secreted proteins may diminish host attractiveness to miracidia. These findings provide a list of attractant candidates to potentially decrease B. glabrata infection and minimise schistosomiasis.

Introduction

The freshwater snail Bulinus truncatus is one of the main intermediate hosts of urogenital schistosomiasis in Africa, Europe and the Middle East. This snails’ distribution is expected to shift poleward due to climate change, predominately through changes in global temperature and precipitation patterns. However, accurate range shift predictions are hampered by a lack of ecological data on the tolerance limits of this species. Therefore, we carried out a common garden experiment to collect reliable life-history data for Bulinus truncatus under different temperature conditions and assessed its thermal tolerance limits and local adaptation capacity.

Methods

Live snails were collected from nine locations in three different countries across a latitudinal gradient (France, Senegal and Zimbabwe) and were bred in the lab to reduce maternal effects. The second generation offspring was subjected to eight constant temperature treatments ranging from 4°C to 36°C. Life history data (growth, fecundity and survival) was collected every week for 12 weeks and physiological and genetic analyses will be carried out in the near future to assess the snail’s thermal tolerance limits, thermal optima and local adaptation capacity.

Results

The experiment is still ongoing and the first results of the life history data analysis are expected to be presented at ICOPA 2022.

Conclusions

The collected data can be used to construct mechanistic niche models that accurately predict Bulinus truncatus’ future distribution under different climate change scenarios and thereby assist in global schistosomiasis risk assessment.

Introduction

Although Bulinus and Schistosoma have been studied in the Lake Victoria Basin in Kenya for years, there remains considerable uncertainty regarding the species of Bulinus present and their possible roles in transmission of S. haematobium. Our goal was to examine the bulinid species present and the schistosome infections they naturally carry, including their involvement in transmission in the lake itself.

Methods

Collections of Bulinus and their trematode parasites were made at 11 survey sites in and around Lake Victoria. Sequences from representative Bulinus specimens (partial cox1 and 16s) and schistosomes (partial cox1 and ITS) were used for phylogenetic analyses.

Results

We examined 6,113 bulinids, and identified 8 distinct taxa, including four from the lake. Schistosoma haematobium infections were found in Bulinus globosus and B. productus, neither of which were recovered from the lake. Schistosoma bovis infections were found in four species, including the two aforementioned taxa as well as B. forskalii and B. ugandae, the latter species recovered from the lake.

Conclusions

Whereas S. haematobium and S. bovis are commonly transmitted in waterbodies away from the lake, only S. bovis was found in lake-dwelling snails, rarely from B. ugandae. We note that B. ugandae, the bulinid species commonly found from the lake shore, is often either misidentified as B. globosus or its status as a distinct species not clearly recognized. This is relevant because its persistent lack of compatibility with S. haematobium lies at the heart of why urinary schistosomiasis transmission in the lake is rare.

Introduction

We seek to find innovative ways to interfere with schistosome growth and development, targeting the intramolluscan sporocyst stages as a model system. In Kenyan snails, echinostome rediae are typically competitively dominant to Schistosoma mansoni sporocysts. Rediae of Echinostoma caproni do not consume S. mansoni sporocysts but nonetheless stunt their in vivo development. We hypothesize that this effect is mediated by excretory/secretory products (ESPs) produced by rediae. We seek to characterize this inhibitory effect.

Methods

E. caproni rediae harvested from infected snails were allowed to condition minimal, protein-free culture medium 199 for 24 h. Unconditioned control and rediae-conditioned media were flash-frozen and submitted for MS/MS analysis (Orbitrap Eclipse). Proteins were identified using MaxQuant and Scaffold Q+S software in reference to available E. caproni adult proteome and genome information.

Results

Thus far, 340 E. caproni proteins have been identified. The majority were peptidases such as metallo, serine, and threonine peptidases, parasite detoxification proteins such as, thioredoxin, glutathione transferase, and calreticulin, and additionally uncharacterized proteins. Control preparations were negative for ESPs.

Conclusions

A surprising diversity of proteins was found to be secreted by rediae, many of which could potentially have detrimental effects on S. mansoni sporocysts. Comparisons with ESPs from other larval trematodes, including S. mansoni are underway. Future studies will examine small molecules produced by rediae and compare the secretory profiles of other trematode larvae dominant to S. mansoni.
This study was supported by NIH grant R37 AI101438.

Introduction

The freshwater snail Biomphalaria glabrata is the intermediate host of Schistosoma mansoni, parasite agent of human intestinal schistosomiasis. The innate immune system constitutes a complex black box, in which the immune cells (called hemocytes) play a major role in both cellular and humoral response towards pathogens. Characterization of these hemocytes from the litterature is based on morphology after cell plating. However, depending of the authors, from 2 to 5 hemocyte populations were described. In this study we proposed to evaluate the hemocyte populations complexity at the transcriptomic level.

Methods

We proposed to use single cell RNA sequencing technology using a droplet-based system to separate hemocytes and to sequence their transcriptome at a single cell level.

Results

Using this technic we were able to demonstrate the presence of 7 hemocytes transcriptomic populations defined by the expression of specific marker genes. Data analysis from transcriptomic and morphological studies do not allow to establish a correlation between hemocyte populations defined by these two kind of approaches. As a result, this study provides a detailed description of different hemocyte transcriptomic populations in B. glabrata supported by distinct cellular functions.

Conclusions

Using innovative omic approach, this work opens a new field of study in the hemocytes characterization and in their potential response to pathogens, in particular towards S. mansoni parasites.

Introduction

Global changes are reshaping the distribution of vector-borne diseases by spreading vectors beyond to previously non-endemic areas. Since 2013, urogenital bilharziasis has emerged in Corsica and threats European countries. Humans become infected when they meet freshwater bodies infested with schistosome larvae that are released from gastropod vectors. Monitoring schistosomiasis host vectors is a prerequisite to understand and subsequently to control this pathogen transmission. Because malacological surveys are time consuming and necessitate special expertise, the use of a simple molecular method is desirable. The aim of ELABU project is to develop a rapid diagnostic LAMP (Loop-mediated isothermal amplification) tool to detect the environmental DNA of Bulinus truncatus, vector of Schistosoma haematobium. Interestingly, LAMP method possesses all the characteristics required for adaptability to field conditions particularly in low-income countries: speed, simplicity, low cost, robustness against inhibitors.

Methods

We have tested this new method on Corsican water samples already analyzed by qPCR and ddPCR.

Results

We demonstrate that our diagnostic tool possesses high sensitivity compared to the two other methods which are not field adapted.

Conclusions

LAMP detection of environmental DNA (eLAMP) makes large-scale sensitive surveillance of urogenital Bilharziasis possible by identifying potentially threatened areas. More generally eLAMP method has great potential in vector-borne diseases and ecology.

Introduction

Trematode parasites generally use freshwater snails as obligate intermediate hosts in their lifecycle. A single snail species often serves as an intermediate host for several co-occurring trematode species. This can lead to within-host interactions that can impact infection outcome and subsequent transmission to the final host. Additionally, recent research has emphasized the importance of the snail microbiome in susceptibility to trematode infections. Therefore, it is paramount to document microbiome and trematode communities within individual snail species from natural settings. We focus on a highly endemic setting for schistosomiasis in the Senegal River Basin (SRB). Following the embankment of the Senegal River in the 1980s, a major outbreak of intestinal schistosomiasis occurred. Yet, nowadays, the urinary form is highly prevalent, a shift that remains hitherto unexplained. This study aims to characterize the microbiome and trematode communities of Biomphalaria and Bulinus snail species sampled along the SRB to assess their role in the susceptibility towards schistosome infection.

Methods

Snails collected from five localities across the SRB in 2012, 2014 and 2021 are studied. First, a rapid diagnostic PCR is applied to detect infected snails. Second, an amplicon sequencing workflow is used to genotype 10 infected snails per species per site and their infecting trematodes. Finally, 16S metabarcoding is applied to map the microbiome of five non-, five single- and five co-infected snails per species per site.

Results

Patterns of genetic diversity, microbiome, and trematode communities of snail hosts in the SRB will be presented and discussed.

Conclusions

This will provide greater insight into the processes that influence disease dynamics.