Multi-strain compatibility polymorphism between a parasite and its snail host, a neglected vector of schistosomiasis in Africa

Priority knowledge gaps for schistosomiasis research and development in the World Health Organization Africa Region

Schistosomiasis, also known as bilharzia, is a widespread neglected tropical disease (NTD) in Africa, with more significant research and development (R&D) challenges and gaps compared to other preventive chemotherapy NTDs (PC-NTDs) like onchocerciasis, lymphatic filariasis, and trachoma. In response to this challenge, some global initiatives have advocated for bridging this gap, focusing on coordinated engagement with research donors. In this opinion article we highlight key R&D priorities for combating schistosomiasis in the WHO Africa region. These include defining morbidity indicators, expanding prevention, and developing innovative diagnostics, treatments, and public health strategies like test-and-treat. We emphasize integrating efforts with broader health campaigns, assessing zoonotic transmission through One Health, and using environmental surveillance tools like xenomonitoring and eDNA. We stress the need to study climate and environmental impacts on transmission, zoonotic transmission, schistosome hybridization, and snail ecology, advancing snail control, and developing vaccines, while calling for new treatments beyond praziquantel, addressing drug resistance, and improving access for children and remote populations. Further, operational research should refine hotspot interventions, enhance water, sanitation and hygiene integration, and address socio-cultural barriers. Lastly, sustainable funding and global collaboration are vital to achieve 2030 NTD Roadmap goals.

A RAPID DIAGNOSTIC PCR ASSAY FOR THE DETECTION OF SCHISTOSOMA MANSONI IN THEIR SNAIL VECTORS

Accurate detection of schistosome infections in snails is vital for epidemiologic and laboratory studies. Traditional microscopy methods to detect schistosomes in snails are hindered by long prepatent periods and snail survivorship, leading to inaccurate assessment of infections. A rapid, multiplexed PCR assay targeting Biomphalaria sudanica or Biomphalaria glabrata (internal control) and Schistosoma mansoni DNA is described. The method takes less than 90 min starting from extracted snail DNA and is successful at amplifying schistosome DNA in snail tissue as soon as 30 min following exposure. Accurate measures of schistosome infection success in snails (compatibility) are possible by 4-7 days postexposure.

The genome and transcriptome of the snail Biomphalaria sudanica s.l.: immune gene diversification and highly polymorphic genomic regions in an important African vector of Schistosoma mansoni

BACKGROUND

Control and elimination of schistosomiasis is an arduous task, with current strategies proving inadequate to break transmission. Exploration of genetic approaches to interrupt Schistosoma mansoni transmission, the causative agent for human intestinal schistosomiasis in sub-Saharan Africa and South America, has led to genomic research of the snail vector hosts of the genus Biomphalaria. Few complete genomic resources exist, with African Biomphalaria species being particularly underrepresented despite this being where the majority of S. mansoni infections occur. Here we generate and annotate the first genome assembly of Biomphalaria sudanica sensu lato, a species responsible for S. mansoni transmission in lake and marsh habitats of the African Rift Valley. Supported by whole-genome diversity data among five inbred lines, we describe orthologs of immune-relevant gene regions in the South American vector B. glabrata and present a bioinformatic pipeline to identify candidate novel pathogen recognition receptors (PRRs).

RESULTS

De novo genome and transcriptome assembly of inbred B. sudanica originating from the shoreline of Lake Victoria (Kisumu, Kenya) resulted in a haploid genome size of ~ 944.2 Mb (6,728 fragments, N50 = 1.067 Mb), comprising 23,598 genes (BUSCO = 93.6% complete). The B. sudanica genome contains orthologues to all described immune genes/regions tied to protection against S. mansoni in B. glabrata, including the polymorphic transmembrane clusters (PTC1 and PTC2), RADres, and other loci. The B. sudanica PTC2 candidate immune genomic region contained many PRR-like genes across a much wider genomic region than has been shown in B. glabrata, as well as a large inversion between species. High levels of intra-species nucleotide diversity were seen in PTC2, as well as in regions linked to PTC1 and RADres orthologues. Immune related and putative PRR gene families were significantly over-represented in the sub-set of B. sudanica genes determined as hyperdiverse, including high extracellular diversity in transmembrane genes, which could be under pathogen-mediated balancing selection. However, no overall expansion in immunity related genes was seen in African compared to South American lineages.

CONCLUSIONS

The B. sudanica genome and analyses presented here will facilitate future research in vector immune defense mechanisms against pathogens. This genomic/transcriptomic resource provides necessary data for the future development of molecular snail vector control/surveillance tools, facilitating schistosome transmission interruption mechanisms in Africa.

The genome and transcriptome of the snail Biomphalaria sudanica s.l.: Immune gene diversification and highly polymorphic genomic regions in an important African vector of Schistosoma mansoni

Background

Control and elimination of schistosomiasis is an arduous task, with current strategies proving inadequate to break transmission. Exploration of genetic approaches to interrupt Schistosoma mansoni transmission, the causative agent for human intestinal schistosomiasis in sub-Saharan Africa and South America, has led to genomic research of the snail vector hosts of the genus Biomphalaria. Few complete genomic resources exist, with African Biomphalaria species being particularly underrepresented despite this being where the majority of S. mansoni infections occur. Here we generate and annotate the first genome assembly of Biomphalaria sudanica sensu lato, a species responsible for S. mansoni transmission in lake and marsh habitats of the African Rift Valley. Supported by whole-genome diversity data among five inbred lines, we describe orthologs of immune-relevant gene regions in the South American vector B. glabrata and present a bioinformatic pipeline to identify candidate novel pathogen recognition receptors (PRRs).

Results

De novo genome and transcriptome assembly of inbred B. sudanica originating from the shoreline of Lake Victoria (Kisumu, Kenya) resulted in a haploid genome size of ~944.2 Mb (6732 fragments, N50=1.067 Mb), comprising 23,598 genes (BUSCO=93.6% complete). The B. sudanica genome contains orthologues to all described immune genes/regions tied to protection against S. mansoni in B. glabrata. The B. sudanica PTC2 candidate immune genomic region contained many PRR-like genes across a much wider genomic region than has been shown in B. glabrata, as well as a large inversion between species. High levels of intra-species nucleotide diversity were seen in PTC2, as well as in regions linked to PTC1 and RADres orthologues. Immune related and putative PRR gene families were significantly over-represented in the sub-set of B. sudanica genes determined as hyperdiverse, including high extracellular diversity in transmembrane genes, which could be under pathogen-mediated balancing selection. However, no overall expansion in immunity related genes were seen in African compared to South American lineages.

Conclusions

The B. sudanica genome and analyses presented here will facilitate future research in vector immune defense mechanisms against pathogens. This genomic/transcriptomic resource provides necessary data for the future development of molecular snail vector control/surveillance tools, facilitating schistosome transmission interruption mechanisms in Africa.