An African or Asian evolutionary origin for human schistosomes?

The origin and the evolution of Schistosomatidae Species, due to their medi cal importance (responsible of the second most important human parasitosis after malaria), arouse a great interest. A combination of phylogenetic stud ies using several molecular markers has provided support for the traditiona l grouping and evolutionary inferences derived from morphological and biolo gical data. The genus Schistosoma, which comprises all species parasitizing Man, is generally split into four evolutionary lineages (mansoni, haematob ium, indicum and japonicum lineages). The group of African schistosomes (in cluding mansoni and haematobium lineages) appears very divergent from the j aponicum lineage. Recent phylogenetic Studies using partial 28S rDNA sequen cing and including Orientobilharzia turkestanicum from Iran, an Asian paras ite of livestock, found, unexpectedly, that this species nested among Schis tosoma species, thus rendering the latter paraphyletic, and suggested an As ian origin for the Schistosoma genus. The present work re-examines the ques tion of the geographical origin of human schistosomes by analysing a new ge nomic marker (ITS2) as well as by including the use of O. turkestanicum ori ginating from northeastern China. Our results are in agreement with previou s work using 28S, in demonstrating that Schistosoma is not monophyletic. Ho wever, O. turkestanicum, whatever the method of analysis used (distance or parsimony), was grouped with members of the japonicum group to the exclusio n Of African Schistosoma species. Then, our data argue strongly for the nee d for further phylogenetic study including new taxa and new genomic sequenc es before definitely concluding either an Asian or African origin for the g enus Schistosoma. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.