The phylogenetic placement of Taenia cestodes that parasitize humans.

We estimated phylogenetic relationships among 12 species or variants of the cestode genus Taenia, including all 3 species that typically use humans as the definitive host, using published sequences of cytochrome c oxidase subunit I (COI) and 28s rDNA. Analyses of all the data combined using maximum parsimony, neighbor-joining, and maximum likelihood methods give well resolved trees. The trees are similar regardless of the analytical method used. Most of the phylogenetically informative characters are contained in the COI sequence, and trees obtained from analyses of COI alone are similar to the combined data trees. All of the phylogeny estimates suggest that Taenia tapeworms have switched from carnivore definitive hosts to human definitive hosts twice in their history. This result is also supported by bootstrap analyses using all 3 of the above methods of phylogeny estimation.