Bulinus coulboisi of Lake Tanganyika: assessment of its taxonomic position and role as intermediate host for S. haematobium

Summary

The freshwater snail Bulinus coulboisi (Bourguignat) has been reported by previous authors to occur in a large area of central and eastern Africa, and to be a potential intermediate host for Schistosoma haematobium. In order to establish the taxonomic position of B. coulboisi, the present authors made observations on preserved specimens from the type-locality on the western shore of Lake Tanganyika, and on snails collected alive at Kigoma on the eastern shore. Information is presented for the shell, radula, copulatory organ, egg proteins, certain enzymes and chromosome number. The tetraploid chromosome number (2n=72), biochemical features and morphological characteristics of our materials provide evidence that B. coulboisi is a southern form of B. truncatus (Audouin, 1827). The latter species is widespread in northern Africa and is an important intermediate host for S. haematobium, particularly in Egypt and Sudan. The present observations and those of other authors indicate that B. coulboisi lives in small waterbodies, marshes and tributaries associated with Lake Tanganyika, but not in the main body of the lake.

Laboratory-bred B. coulboisi originating from Kigoma gave no patent infections following exposure to a strain of S. haematobium normally carried by a member of the B. africanus group. Only a low degree of compatibility was observed with one of the two tested parasite strains which are normally carried by a member of the B. truncatus group. From the known distribution of urinary schistosomiasis it appears that S. haematobium is represented in western Tanzania by a strain adapted, perhaps exclusively, to the B. africanus group. It is concluded that if B. coulboisi and B. truncatus have any potential importance as intermediate hosts in this region, it will depend upon the introduction of a compatible strain of parasite.