Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 1999
Publication Date: N/A
Interpretive Summary: Many protozoan parasites of man and animals appear similar under light microscopy. Differentiating these parasites thus requires more sensitive, genetic techniques that are based on DNA sequence differences. The purpose of the present study was to test the hypothesis that two closely related protozoan parasites, Hammondia heydorni and Neospora caninum, both parasites of dogs were distinct species. This work was also undertaken to develop genetic methods for differentiating these parasites from one another given that their morphology is so similar. DNA sequencing was performed on DNA encoding ribosomal DNA which contains highly conserved and highly variable regions. The DNA sequences were aligned and analyzed in computer programs that showed N. caninum and H. heydorni to be unique species. This work also allowed for the development of reagents for identifying these parasites in environmental samples which will be helpful in studying the epidemiology of the diseases caused by them.
The complete sequence of the 18S small subunit (SSU) ribosomal DNA of Hammondia hammondi and Sarcocystis mucosa was obtained and compared to SSU rDNA sequences of Neospora caninum, Toxoplasma gondii, Besnoitia Besnoiti, two species of Frenkelia, three species of Isospora and thirteen species of Sarcocystis. Analyses showed H. hammondi and T. gondii are monophyletic and these taxa shared a common ancestor with N. caninum and B. besnoiti. The weight of evidence shows that S. mucosa, S. neurona and Frenkelia species form a clade thereby supporting the conclusion that Sarcocystis is paraphyletic.