ITS2 RIBOSOMAL-RNA INDICATES SCHISTOSOMA-HIPPOPOTAMI IS A DISTINCT SPECIES

The internal transcribed spacer region of the ribosomal RNA, ITS2, was sequenced from a single specimen of S. hippopotami collected from a p ulmonary artery of the hippopotamus, Hippopotamus amphibius in South A frica. The nucleotide sequence was aligned with those of S. mansoni S. rodhaini, S. haematobium, S. intercalatum, S. curassoni, S. bovis and S. japonicum. Both maximum parsimony and genetic distance analyses we re performed on these data sets. Using S. japonicum as outgroup to the African schistosomes, a single most-parsimonious tree was obtained of length 64 steps with a consistency index of 1. S. hippopotami was the sister-group to the remaining African species. This species has later al-spined eggs and its basal position in the tree suggests that this c ondition is primitive and that terminal-spined eggs developed secondar ily. Molecular data clearly show that S. hippopotami cannot be conside red synonymous with S. mansoni. Assuming the hippopotamus is the norma l host of S. hippopotami, phylogenetic analysis is consistent with an ancient association between schistosomes and ungulates.