Novel sequences of schistosomes and their snail intermediate host species in the Democratic Republic of Congo: first phylogenetic analyses

Abstract

Malacological surveys were conducted in 2021 in the Kimpese region of Central Kongo Province, west of the Democratic Republic of Congo (DRC). Snail specimens were collected following a standardised protocol, identified using morphological and molecular methods, and tested for schistosome infection using a diagnostic PCR assay. Positive snail samples were sequenced to characterise the infecting schistosome species. Partial mitochondrial cytochrome c oxidase subunit 1 (COX1) gene sequences were used in phylogenetic analyses to explore the evolutionary position of these snail species within the broader African context. At least four intermediate snail hosts were identified: <i>Bulinus truncatus</i>, <i>Bulinus forskalii</i>, <i>Biomphalaria pfeifferi</i>, and a <i>Biomphalaria</i> species belonging to the Nilotic species complex (tentatively named <i>Biomphalaria</i> cf <i>sudanica)</i>, of which the species identity needs to be confirmed. A total of 37 out of 1,196 snails (3.1%) tested positive for schistosome infection, with an infection prevalence of 7.4% for <i>B. truncatus</i> with <i>Schistosoma haematobium</i> and 1.5% for <i>Biomphalaria</i> spp. with <i>Schistosoma mansoni.</i> The <i>S. mansoni</i> sequence retrieved from these samples formed a basal clade relative to Zambian isolates, whereas <i>S. haematobium</i> grouped with the most frequently characterised haplotype cluster previously identified across mainland Africa. It is important to note that no animal schistosome species were identified in this study. Both the sequences from the snail hosts and the parasites represent novel contributions from the DRC. Additionally, the findings update the current knowledge of schistosomiasis transmission in the Kimpese region by providing insight into the phylogenetic placement, species diversity, and infection status of local snail populations.