NEOTROPICAL SCHISTOSOMIASIS - AFRICAN AFFINITIES OF THE HOST SNAIL BIOMPHALARIA-GLABRATA (GASTROPODA, PLANORBIDAE)

Schistosoma mansoni, the blood fluke responsible for human intestinal schistosomiasis in the Neotropics, was imported repeatedly with Africa n slaves during the period 1500-1800. This trematode, and its intermed iate host snails of the genus Biomphalaria, are widely distributed acr oss Africa and the disease is thought to have quickly become establish ed in South America and the West Indies because of the presence of an endemic susceptible congener, B. glabrata. We compared B. glabrata wit h four other Neotropical and three African species of Biomphalaria usi ng 20 allozyme loci and found that it is phenetically and phylogenetic ally more like the African species; both parasite and American host sn ail are apparently of historically or geologically recent African orig in. Furthermore, genetic distances, cladistic analyses and fossil data suggest the African Biomphalaria species may themselves have evolved from Neotropical founders following an initial trans-Atlantic dispersa l in the reverse direction 2.3-4.5 Mya. Interpretation of existing pat terns remains problematic as few African snails have been characterize d genetically and bath B. glabrata and African B. pfeifferi to compris e several cryptic species. (C) 1997 The Linnean Society of London.