Встречаемость Schistosoma mansoni (Trematoda: Schistosomatidae) у Biomphalaria pfeifferi (Gastropoda: Planorbidae) в водоемах префектуры Киндия (Гвинейская Республика)

Abstract

Mollusks of the genera Biomphalari and Bulinus – intermediate hosts of human-pathogenic Schistosoma trematodes – were found in eight freshwater bodies in the western region of the Kindia Prefecture of Guinea. While Bulinus snails were free from schistosome infection, Biomphalaria specimens were parasitised by the parasite, with infection foci revealed in four water bodies. Morphological analysis of the shells of infected snails confirmed their species as Biomphalaria pfeifferi. The movement behaviour, body shape, internal anatomy, and morphometric characteristics of the cercariae shed from the snails matched those of Schistosoma mansoni. The obtained ITS1 rDNA gene sequences showed 100% identity with homologous loci of S. mansoni from human and rat parasites in Africa and Brazil. In contrast, they differed by 6 nucleotide substitutions from the closest relative, S. rodhaini, and by 2–6 substitutions from S. rodhaini × S. mansoni hybrids. Phylogenetic analysis strongly supported (100% bootstrap) the clustering of the sampled sequences with S. mansoni, distinct from S. rodhaini and hybrid lineages, confirming species identification. This study reports the first documented evidence of S. mansoni infection in B. pfeifferi and its molecular characterization in Guinea. Infected snails (n = 32) were significantly larger on average than uninfected ones (n = 1,110) in samples where trematodes were found. Analysis of environmental factors revealed no effect of pH, dissolved oxygen, or water temperature (within their observed ranges during the study period: October–November) on B. pfeifferi occurrence and S. mansoni infection prevalence. Notably, B. pfeifferi exhibited tolerance to slightly hypoxic conditions (≤5 mg·L^-1 O₂), likely explaining their persistence in excrement-contaminated waters and facilitating schistosome larvae transmission. The presence of schistosomes was associated with specific biocenosis features, including stagnant or slow-flowing water and abundant submerged vegetation. All infected water bodies were located within urban areas. Obtained data are significant for developing schistosomiasis control strategies in the region.

Keywords: Schistosoma, schistosomiasis, natural focus of infection, intermediate hosts, Biomphalaria, ITS1 rDNA, Republic of Guinea