Neotropical schistosomiasis: African affinities of the host snailBiomphalaria glabrata(Gastropoda: Planorbidae)

Abstract

Schistosoma mansoni, the blood fluke responsible for human intestinal schistosomiasis in the Neotropics, was imported repeatedly with African slaves during the period 1500–1800. This trematode, and its intermediate host snails of the genusBiomphalaria, are widely distributed across Africa and the disease is thought to have quickly become established in South America and the West Indies because of the presence of an endemic susceptible congener,B. glabrata. We comparedB. glabratawith four other Neotropical and three African species ofBiomphalariausing 20 allozyme loci and found that it is phenetically and phylogenetically more like the African species; both parasite and American host snail are apparently of historically or geologically recent African origin. Furthermore, genetic distances, cladistic analyses and fossil data suggest the AfricanBiomphalariaspecies may themselves have evolved from Neotropical founders following an initial trans-Atlantic dispersal in the reverse direction 2.3–4.5 Mya. Interpretation of existing patterns remains problematic as few African snails have been characterized genetically and bothB. glabrataand AfricanB. pfeifferiappear to comprise several cryptic species.