Molecular Identification of Radix natalensis as the Prevailing Fasciolosis Vector in Rwanda

Fasciolosis is a neglected zoonotic disease caused by trematode parasites of the genus Fasciola Linnaeus, 1758, which affects both humans and livestock. Current knowledge on the taxonomy and relationship between lymnaeid gastropod intermediate hosts and Fasciola in Rwanda is insufficient and the geographic extent of the endemicity and the lymnaeid species and strains involved in disease transmission remain unknown. We used extensive field surveys (131 localities) in major types of freshwater ecosystems in Rwanda to (1) identify lymnaeid snails using a molecular approach, and (2) characterize genetic diversity in relation to ecological conditions of the potential intermediate host snails. The only lymnaeid species that could be morphologically and genetically identified was Radix natalensis (Krauss, 1848), found across a wide range of different natural and non-natural habitats (50 localities). All newly sequenced Radix specimens from Rwanda cluster within the R. natalensis group and, together with R. natalensis from Kenya, Uganda, and Zimbabwe, form a highly supported clade. However, the relationship of this clade to other R. natalensis specimens was unresolved. The statistical parsimony network analysis of the clade resulted in a single network with 24 unique haplotypes. The haplotypes of the same habitat type (e.g., lakes, rivers, wetlands, and rice plantations) did not form single clusters within this network. This also applies to the comparison between natural and non-natural habitats. We discuss the biogeographical and parasitological implications and compare the new findings with patterns of other lymnaeid species across Africa. Additionally, we suggest further research involving xenomonitoring and eDNA studies.