Malacological Survey and Spatial Distribution of Intermediate Host Snails in Schistosomiasis Endemic Districts of Rwanda

Joseph Kagabo; Chester Kalinda; Project Nshimiyimana; Jean Bosco Mbonigaba; Eugene Ruberanziza; Elias Nyandwi; Nadine Rujeni

doi:10.3390/tropicalmed8060295

Malacological Survey and Spatial Distribution of Intermediate Host Snails in Schistosomiasis Endemic Districts of Rwanda

Trop Med Infect Dis. 2023 May 28;8(6):295. doi: 10.3390/tropicalmed8060295.

Authors

Joseph Kagabo¹, Chester Kalinda², Project Nshimiyimana¹, Jean Bosco Mbonigaba³, Eugene Ruberanziza⁴, Elias Nyandwi⁵, Nadine Rujeni¹

Affiliations

¹ School of Health Sciences, University of Rwanda College of Medicine and Health Sciences, KG 11 Ave., Gasabo, Kigali P.O. Box 3286, Rwanda.
² Bill and Joyce Cummings Institute of Global Health, University of Global Health Equity (UGHE)|Kigali Heights, Plot 772 KG 7 Ave., Kigali P.O. Box 6955, Rwanda.
³ Rwanda Biomedical Centre (RBC) KG 644 St., Kigali P.O. Box 7162, Rwanda.
⁴ The End Fund, 2 Park Avenue, 28th Floor, New York, NY 10016, USA.
⁵ Centre for Geographic Information Systems and Remote Sensing (CGIS), University of Rwanda College of Science and Technology, KN 67 Street, Nyarugenge, Kigali P.O. Box 3900, Rwanda.

Abstract

Background: Schistosomiasis, due to S. mansoni, is prevalent in Rwanda. However, there is a paucity of information related to the abundance, species, distribution, and infectivity of Schistosoma intermediate host snails.

Methods: Snails were collected from 71 sites, including lakeshores and wetlands. Snails obtained were morphologically identified, and cercariae were shed using standard procedures. Cercariae were molecularly characterized using PCR. GPS coordinates were used to generate geospatial maps of snail distribution that were overlaid with geospatial distribution of schistosomiasis among pre-school children in the same areas.

Results: Overall, 3653 snails were morphologically classified as Bulinus spp. and 1449 as Biomphalaria spp. A total of 306 snails shed cercariae, 130 of which were confirmed as S. mansoni cercaria by PCR. There was no significant difference in the proportion of S. mansoni cercariae in wetlands compared to lakeshores.

Conclusion: Rwandan water bodies harbor an important number of snails that shed S. mansoni cercariae. Furthermore, a strong spatial correlation was observed between the distribution of schistosomiasis in children and the spatial distribution of snail infectivity with S. mansoni. The presence of Bulinus spp. Suggests a potential risk of S. haematobium, although molecular analysis did not show any current transmission of this parasite.

Keywords: Biomphalaria; Bulinus; cercariae; malacology; schistosomiasis.

Grants and funding

This research was commissioned by the National Institute for Health Research (NIHR) Global Health Research programme (16/136/33) using UK aid from the UK Government. The study was also financially supported by the ITM-DGD Multiyear programme (2022-2026) funded by the Belgian Government, Directorate-General for Development and Humanitarian Aid. The views expressed in this publication are those of the authors and not necessarily those of the NIHR, the UK Department of Health and Social Care or the DGD.