Molecular characterization and distribution of Schistosoma cercariae collected from naturally infected bulinid snails in northern and central Côte d’Ivoire

Abstract

BackgroundAccurate identification of schistosome species infecting intermediate host snails is important for understanding parasite transmission, schistosomiasis control and elimination. Cercariae emerging from infected snails cannot be precisely identified morphologically to the species level. We used molecular tools to clarify the distribution of the Schistosoma haematobium group species infecting bulinid snails in a large part of Côte d’Ivoire and confirmed the presence of interspecific hybrid schistosomes.MethodsBetween June 2016 and March 2017, Bulinus snails were sampled in 164 human-water contact sites from 22 villages of the northern and central parts of Côte d’Ivoire. Multi-locus genetic analysis (mitochondrial cox1 and nuclear ITS) was performed on individual schistosome cercariae shed from snails, in the morning and in the afternoon, for species and hybrid identification.ResultsOverall, 1923 Bulinus truncatus, 255 Bulinus globosus and 1424 Bulinus forskalii were obtained. Among 2417 Bulinus screened, 25 specimens (18 B. truncatus and seven B. globosus) shed schistosomes, with up to 14% infection prevalence per site and time point. Globally, infection rates per time point ranged between 0.6 and 4%. Schistosoma bovis, S. haematobium and S. bovis × S. haematobium hybrids infected 0.5%, 0.2% and 0.4% of the snails screened, respectively. Schistosoma bovis and hybrids were more prevalent in B. truncatus, whereas S. haematobium and hybrid infections were more prevalent in B. globosus. Schistosoma bovis-infected Bulinus were predominantly found in northern sites, while S. haematobium and hybrid infected snails were mainly found in central parts of Côte d’Ivoire.ConclusionsThe data highlight the necessity of using molecular tools to identify and understand which schistosome species are transmitted by specific intermediate host snails. The study deepens our understanding of the epidemiology and transmission dynamics of S. haematobium and S. bovis in Côte d’Ivoire and provides the first conclusive evidence for the transmission of S. haematobium × S. bovis hybrids in this West African country.Trial registration ISRCTN, ISRCTN10926858. Registered 21 December 2016; retrospectively registered (see: http://www.isrctn.com/ISRCTN10926858)Electronic supplementary materialThe online version of this article (10.1186/s13071-019-3381-3) contains supplementary material, which is available to authorized users.

<p>Genetic Diversity of <em>Schistosoma haematobium</em> in Qena Governorate, Upper Egypt</p>

“…Hybridization and introgression with other Schistosoma species are reported in other parts of Africa. [53][54][55] However, hybridization could not be confirmed in the present study in the absence of comparative control isolates of different schisosomes species..…”

Snail-Related Contributions from the Schistosomiasis Consortium for Operational Research and Evaluation Program Including Xenomonitoring, Focal Mollusciciding, Biological Control, and Modeling

“…Accurate differentiation among Schistosoma species and associated hybrids using cercarial morphology is not routinely feasible; molecular analysis is needed to confirm the species. 23,24 This is important for evaluating transmission and testing assumptions made in relation to the schistosome species being transmitted, based on geography, the type of study being conducted, and the snail species involved. 25,26 The prepatent (or latent) infection period spans the time between penetration of the snail by a miracidium and the emergence of cercariae.…”

Contributions of the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) to Schistosomiasis Control and Elimination: Key Findings and Messages for Future Goals, Thresholds, and Operational Research

“…In addition, these investigations yielded new findings about the composition and distribution of naturally occurring S. haematobium/ Schistosoma bovis hybrids across Niger. 32,33 Such data and tools developed with SCORE support could prove useful in evaluating potential animal reservoirs that could perpetuate transmission. 31 All new schistosome DNA sequences generated from this work have been deposited in the NCBI GenBank open-access sequence repository for access by other researchers.…”