Molecular characterisation of Bulinus snails – intermediate hosts of schistosomes in Ogun State, South-western Nigeria

Olaoluwa Akinwale,Oyetunde Salawu,Opeyemi Oso,Ting-Wen Chen,Alexander Odaibo,Petrus Tang,Pam Gyang

doi:10.12657/folmal.023.009

Abstract

Freshwater snails of the genus Bulinus O. F. Muller, 1781 are intermediate hosts for schistosomes, trematode parasites which cause schistosomiasis. The genus includes closely related species complexes with restricted gene flow between populations of each taxon. Despite their importance as intermediate hosts, unambiguous identification of these snails remains challenging. We applied molecular approach to their identification to achieve a better understanding of the epidemiology of schistosomiasis in an endemic region, south-western Nigeria. A total of 149 snails were collected and their genomic DNA was screened for schistosome infection using PCR amplification of schistosome DraI repeat sequence. The snails were identified by PCR-RFLP and/or sequencing of an amplicon of their entire ITS region including the 5.8S ribosomal RNA (rRNA) gene. Four Bulinus species, namely B. globosus (Morelet, 1866), B. forskalii (Ehrenberg, 1831), B. camerunensis Mandahl-Barth, 1957 and B. senegalensis O. F. Muller, 1781 were identified, and 34.9% (n = 52) of the 149 snails were infected: B. globosus 25.5% (n = 38), B. forskalii 5.4% (n = 8), B. camerunensis 2.7% (n = 4) and B. senegalensis 1.3% (n = 2). Restriction fragment profiles of the ribosomal ITS region for B. globosus closely matched those obtained in our previous study thus confirming the view that ribosomal ITS region of these snails could be well suited for taxonomic studies. The use of sequencing for species identification was costly and time-consuming, but it was effective in resolving true identities of snails whose restriction profiles were similar and inconclusive. key wOrds: species identification, Bulinus, ITS, rRNA gene, schistosome, schistosomiasis, Nigeria

Highlights

Schistosomiasis, an infection caused by blood flukes of the genus Schistosoma Weinland, 1858, is endemic in Nigeria (Akogun & Akogun 1996, Mafe et al 2000)
1781 and Biomphalaria Preston, 1910 act as intermediate hosts for the parasites; the snails occur commonly throughout much of Africa and its adjacent regions. Their focal distribution has been reported in many parts of Nigeria (Okwuosa & Ukoli 1980, Imevbore et al 1988, Ndifon & Ukoli 1989, Ofoezie 1999, Owojori et al 2006) where Biomphalaria pfeifferi (Krauss, 1848), Bulinus globosus (Morelet, 1866) and B. truncatus (Audouin, 1827) were recorded from diverse freshwater habitats
Urinary schistosomiasis is caused by S. haematobium, with some snails of the genus Bulinus acting as the intermediate hosts

Summary

Introduction

Schistosomiasis, an infection caused by blood flukes of the genus Schistosoma Weinland, 1858, is endemic in Nigeria (Akogun & Akogun 1996, Mafe et al 2000). F. Müller, 1781 and Biomphalaria Preston, 1910 act as intermediate hosts for the parasites; the snails occur commonly throughout much of Africa and its adjacent regions. 1781 and Biomphalaria Preston, 1910 act as intermediate hosts for the parasites; the snails occur commonly throughout much of Africa and its adjacent regions Their focal distribution has been reported in many parts of Nigeria (Okwuosa & Ukoli 1980, Imevbore et al 1988, Ndifon & Ukoli 1989, Ofoezie 1999, Owojori et al 2006) where Biomphalaria pfeifferi (Krauss, 1848), Bulinus globosus (Morelet, 1866) and B. truncatus (Audouin, 1827) were recorded from diverse freshwater habitats.

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