Distribution and habitats of Biomphalaria pfeifferi, snail intermediate host of Schistosoma mansoni, in South Africa

As intermediate host for Schistosoma mansoni, Biomphalaria pfeifferi plays a major role in the transmission of intestinal bilharziasis in the endemic areas of South Africa. This article focuses on the geographical distribution and habitats of this species, as reflected by the 1 639 samples on record in the database of the National Freshwater Snail Collection of South Africa. This snail is well represented in the Northern Province, Mpumalanga and the coastal areas of KwaZulu-Natal, that represent the bilharzia endemic areas of South Africa. Details of each habitat, as well as mean altitude and mean annual temperature and rainfall of each locality, were processed to determine chi-square and effect size values and to construct an integrated decision tree that makes a selection of those variables that could maximally discriminate between this snail and all the other species in the database. The results indicated that temperature and type of water-body are the major factors determining the distribution of B. pfeifferi in South Africa. These findings support the results of demographic studies reported by several authors that led them to the conclusion that B. pfeifferi does best under warm stable conditions. The importance of four isolated and persistent foci occurring further west than the western arm of its range of distribution and far removed from the bilharzia endemic areas, is discussed. Two of these localities are popular holiday resorts and the fact that specimens from both these localities showed a high compatibility with a local strain of S. mansoni is cause for concern