Molecular phylogenetics of diphyllobothriid cestodes with special reference to the species identification of Sparganum proliferum.

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Sparganum proliferum (Ijima, 1905) is a larval cestode and an etiological agent of proliferative human sparganosis, which is characterized by its agamogenesis by continuous branching and budding in the human body, and invasions on every kind of organs and tissues. Since the first finding by Ijima (J.Coll.Sci.Imp.Univ.Tokyo, 20 : 1-21, 1905), a total of 14 clinical cases has been reported in the world and all of them were fatal. The adult stage of this larval cestode and the life cycle including the final and intermediate hosts in nature has not yet been known in spite of the high medical importance of proliferative human sparganosis.Previous works on S.proliferum has been concentrated in comparison with a putative related species, Spirometra erinaceieuropaei (Rudolphi, 1819)[Platyheiminth : Cestoda : Pseudophyllidea : Diphyllobothriidae], of which larval stage plerocercoid also causes human sparganosis. However significant definitions of S.proliferum are the larval agamous development … More and mortal disease caused by it. Thus, earlier works were summarized that S.proliferum might be abnormally developed Spiro.erinaceieuropaei. While, recently, Kokaze et al.(Parasitol.Internat., 46 : 271-279, 1997) analyzed NADH dehydrognase subunit I (NDIII) gene encoded in the mitochondrial DNA (mtDNA) and revealed that S.proliferum was closely related with Spiro.erinaceieuropaei but both contained differentiable NDIII gene sequence.In this study, we focused on species identification of S.proliferum based on molecular phylogenetic studies. First, we analyzed mitochondrial cytochrome c subunit I (COI) gene sequence of S.proliferum, Spiro.erinaceieuropaei and Diphyllobothrium nihonnkaiense Yamane et al., 1986 [Diphyllobothriidae] to construct phylogenetic tree including teniid cestodes [Cyclophyllidea : Teniidae], and revealed that S.proliferum clearly identified as an pseudophyllidean cestode, also showing high sequence similarity with Spiro.erinaceieuropaei. Second, six species of diphyllobothriids obtained from marine mammalian hosts were added in the analyses. Every phylogenetic analysis failed to find out the species which contained identical sequences or more closely related with S.proliferum, but revealed that the divergence between the cluster included S.proliferum and Spiro.erinaceieuropaei, and the marine species cluster had taken place in earlier period. In addition, the genetic distance between S.proliferum and Spiro. erinaceieuropaei was comparative with or more distant than those between marine species. These results indicate that S.proliferum derived from fresh water origin and may be distinctive species from Spiro.erinaceieuropaei. Less