Intraspecific variation of Spirometra erinaceieuropaei and phylogenetic relationship between Spirometra and Diphyllobothrium inferred from mitochondrial CO1 gene sequences

Spirometra erinaceieuropaei is a diphyllobothriid cestode whose adult stage occurs mainly in cat-like carnivores, but occasionally in canids and humans. Although it is generally accepted that the distribution of S. erinaceieuropaei is cosmopolitan, it is controversial as to whether all of S. erinaceieuropaei reported are the same species. This study determined partial sequences of the CO1 gene from several isolates in Asian countries and compared them to sequence data from the GenBank/EMBL/DDBJ nucleotide sequence database. Then intraspecific variation of S. erinaceieuropaei and its phylogenetic relationship with Diphyllobothrium were evaluated. The level of nucleotide variation in the CO1 gene sequences within S. erinaceieuropaei was less than 2.6%. Although it was a little larger than that within each species of Diphyllobothrium (0.1–1.0%), it was much smaller than the interspecific variation within the genus Diphyllobothrium (6.2–14%). These facts indicate that all isolates of S. erinaceieuropaei used in this study, which were collected from Asia, Australia and New Zealand, belong to the same species. Based on CO1 gene sequences, genus Spirometra is clearly separate from the genus Diphyllobothrium. It seems that the genus Spirometra is not a synonym of the genus Diphyllobothrium. The phylogenetic relationship between S. erinaceieuropaei and Sparganum proliferum inferred from the CO1 gene clearly confirm the previous opinion that S. proliferum is a distinct species from S. erinaceieuropaei.