Transmission and diversity of Schistosoma haematobium and S. bovis and their freshwater intermediate snail hosts Bulinus globosus and B. nasutus in the Zanzibar Archipelago, United Republic of Tanzania
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Background The Zanzibar Archipelago (Pemba and Unguja islands) is targeted for the elimination of human urogenital schistosomiasis caused by infection with Schistosoma haematobium where the intermediate snail host is Bulinus globosus. Following multiple studies, it has remained unclear if B. nasutus (a snail species that occupies geographically distinct regions on the Archipelago) is involved in S. haematobium transmission on Zanzibar. Additionally, S. haematobium was thought to be the only Schistosoma species present on the Zanzibar Archipelago until the sympatric transmission of S. bovis, a parasite of ruminants, was recently identified. Here we re-assess the epidemiology of schistosomiasis on Pemba and Unguja together with the role and genetic diversity of the Bulinus spp. involved in transmission. Methodology/Principal findings Malacological and parasitological surveys were conducted between 2016 and 2019. In total, 11,116 Bulinus spp. snails were collected from 65 of 112 freshwater bodies surveyed. Bulinus species identification were determined using mitochondrial cox1 sequences for a representative subset of collected Bulinus (n = 504) and together with archived museum specimens (n = 6), 433 B. globosus and 77 B. nasutus were identified. Phylogenetic analysis of cox1 haplotypes revealed three distinct populations of B. globosus, two with an overlapping distribution on Pemba and one on Unguja. For B. nasutus, only a single clade with matching haplotypes was observed across the islands and included reference sequences from Kenya. Schistosoma haematobium cercariae (n = 158) were identified from 12 infected B. globosus and one B. nasutus collected between 2016 and 2019 in Pemba, and cercariae originating from 69 Bulinus spp. archived in museum collections. Schistosoma bovis cercariae (n = 21) were identified from seven additional B. globosus collected between 2016 and 2019 in Pemba. By analysing a partial mitochondrial cox1 region and the nuclear ITS (1–5.8S-2) rDNA region of Schistosoma cercariae, we identified 18 S. haematobium and three S. bovis haplotypes representing populations associated with mainland Africa and the Indian Ocean Islands (Zanzibar, Madagascar, Mauritius and Mafia). Conclusions/Significance The individual B. nasutus on Pemba infected with S. haematobium demonstrates that B. nasutus could also play a role in the local transmission of S. haematobium. We provide preliminary evidence that intraspecific variability of S. haematobium on Pemba may increase the transmission potential of S. haematobium locally due to the expanded intermediate host range, and that the presence of S. bovis complicates the environmental surveillance of schistosome infections.
Pennance , T , Ame , S M , Amour , A K , Suleiman , K R , Muhsin , M A , Kabole , F , Ali , S M , Archer , J , Allan , F , Emery , A , Rabone , M , Knopp , S , Rollinson , D , Cable , J & Webster , B L 2022 , ' Transmission and diversity of Schistosoma haematobium and S. bovis and their freshwater intermediate snail hosts Bulinus globosus and B. nasutus in the Zanzibar Archipelago, United Republic of Tanzania ' , PLoS Neglected Tropical Diseases , vol. 16 , no. 7 , e0010585 . https://doi.org/10.1371/journal.pntd.0010585
PLoS Neglected Tropical Diseases
Copyright: © 2022 Pennance et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
DescriptionFunding: The study was partially funded by a Wellcome Trust Seed Award (https://wellcome.org) grant number 207728 (awarded to BLW). TP was funded by the NERC GW4+ DTP (https://www.nercgw4plus.ac.uk) and the Natural Environmental Research Council (https://www.nerc.com), number NE/L002434/1. Data and samples from the ZEST project were also used in the current study, ZEST was funded by the University of Georgia Research Foundation Inc., which is funded by the Bill & Melinda Gates Foundation (https://www. gatesfoundation.org/) for the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE; https://score.uga.edu/) projects (prime award no. 50816, subaward no. RR374-053/4893206 to DR). FA, AE and MR were funded by the Wellcome Trust (https://wellcome.org), for the SCAN: Schistosomiasis Collection at the Natural History Museum, grant number 104958/Z/14/Z, in which many of the ZEST samples were accessioned.
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