Species of Hepatozoon are apicomplexan parasites infecting tetrapod vertebrates and hematophagous arthropods. Two species, Hepatozoon catesbianae and Hepatozoon clamatae, have been described inhabiting the erythrocytes of bullfrogs and green frogs. A number of characteristics typically used to distinguish between members of this genus are shared between these 2 species, prompting speculation as to whether or not these organisms are in fact distinct species. To test the species distinction, bullfrogs and green frogs were captured at various sites across Nova Scotia, blood samples were collected, and DNA was extracted from samples containing parasites. The internal transcribed spacer 1 (ITS-1) from geographically diverse samples of both species was amplified by PCR, sequenced, and analyzed. ITS-1 sequences from the 2 species revealed single-nucleotide polymorphisms at 6 sites. Phylogenetic analysis of these molecular data and cytopathological features place isolates of each species in separate monophyletic groups. Comparison of the ITS-1 sequences between isolates from Nova Scotia and Ontario revealed that ITS-1 sequences of H. catesbianae from a previous study were mischaracterized as being those of H. clamatae. Phylogenetic data based on molecular variation and cytopathological features from this study provide the strongest evidence to date supporting the distinction between these 2 species.

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