Inference of molecular phylogeny of Sarcocystis felis (Sarcocystidae) from cats based on nuclear-encoded ribosomal gene sequences.

The phylogenetic position of four clinical isolates of Sarcocystis felis was assessed using ssurRNA and ITS1 gene sequences in the context of a wide array of other Sarcocystis sp. Phylogenetic reconstructions using neighbour-joining and maximum parsimony methods generated identical tree topologies with strong support values at each node. High ssurRNA sequence similarity (> or =99%) and the resulting phylogeny demonstrated that S. felis and S. neurona are significantly closely related to each other. The two Sarcocystis formed a monophyletic group distinct from the other Sarcocystis sp., irrespective of the alignment algorithms or tree-building method used. The absolute (100%) identity of ssurRNA sequences of sarcocysts and sporocysts obtained from one cat raised the question regarding the cat's role as a potential intermediate host besides its known role as a definitive host of S. felis. On the other hand, S. felis sarcocyst DNA sequence was found to be quite dissimilar over the ITS1 region when compared to S. neurona. These findings indicated that using sequences from two different genetic loci provided a stronger comparative basis than would have been possible using either one.