Molecular characterization of Bulinus globosus and B. nasutus on Zanzibar, and an investigation of their roles in the epidemiology of Schistosoma haematobium

The ribosomal internal transcribed spacer (ITS) regions of both Bulinus globosus and B. nasutus from Zanzibar were amplified and restricted with 6 enzymes. Restriction products were separated by polyacrylamide gel electrophoresis and visualized by ethidium bromide staining. Considerable genetic variation was observed at 3 levels: (i) between species, (ii) among populations and (iii) among individuals. In addition, the 18S ribosomal deoxyribonucleic acid gene was amplified from both species and the products were also restricted with several enzymes. No variation was detected. Nucleotide diversity of the ITS was estimated to be approximately 0.019 for both species and nucleotide divergence between species was estimated to be 0.03. Restriction profiles differentiated these snail species and may prove useful for identification purposes. Only B. globosus populations were found to be naturally infected with Schistosoma haematobium. From laboratory infection studies of progeny snails, B. nasutus appeared to be refractory to S. haematobium, whereas certain B. globosus populations were susceptible to laboratory challenge.