Revising the transmission biology of schistosomiasis in Zanzibar

Tue16  Apr12:54pm(3 mins)
Renold C9


T Pennance2; S M Ame3; A K Amour3; K R Suleiman3; F Allan2; S Knopp4; D Rollinson2; J Cable1; B Webster2
1 Cardiff School of Biosciences, Cardiff University, UK;  2 Natural History Museum, UK;  3 Public Health Laboratory - Ivo de Carneri, Tanzania;  4 Swiss Tropical and Public Health Institute, University of Basel, Basel, Switzerland, Switzerland


The causative agent of urogenital schistosomiasis, Schistosoma haematobium, has historically been considered to be the only schistosome species transmitted specifically through Bulinus globosus on Unguja and Pemba Islands (Zanzibar, United Republic of Tanzania). For insights into the environmental risk of S. haematobium transmission on Pemba, malacological surveys for Bulinus globosus and B. nasutus, closely related and morphologically similar freshwater snail species acting as potential intermediate hosts of S. haematobium were conducted across the island from November 2016 to November 2018. 

Of the 10,871 snails collected during malacological surveys over this time, 19 (0.17%) B. globosus from 5 sites had patent schistosome infections, initially assumed to be S. haematobium. However, when these cercariae were identified by sequencing a region of the cox1 and the nuclear internal transcribed spacer (ITS1+2), schistosomes from seven B. globosus (five in November 2016 and two in November 2018), from a single locality in Kinyasini, were in fact S. bovis, a closely related schistosome species that infects ungulates. In February 2019, a single cow from this site was later diagnosed, through screening faeces, with a S. bovis infection.Moreover, one wild-caught B. nasutus (a species typically considered refractory to infection on Zanzibar) from Kangagani was found to be infected with S. haematobium

These new molecular data implicating B. globosus in the transmission of S. bovis in East Africa and B. nasutus in the transmission of S. haematobium on Pemba, add to earlier observations and complicate on-going transmission monitoring of S. haematobium on the islands.

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