Phylogenetic relationship of Sarcocystis neurona to other members of the family Sarcocystidae based on small subunit ribosomal RNA gene sequence.

This study investigates the evolutionary relationship between a horse disease-causing parasite, Sarcocystis neurona, and other parasites within the same family. The research is based on the analysis of small subunit ribosomal RNA gene sequences and suggests a common ancestor for certain types of these parasites.

Research Method and Analysis

• The researchers focused on the study of Sarcocystis neurona, a parasite that causes neurological disease in horses, particularly in North and South America. The natural host species for this parasite are not yet known, therefore its classification is currently based on ultrastructural analysis.
• The small subunit ribosomal RNA (SSU rRNA) gene of S. neurona was amplified using the polymerase chain reaction (PCR) techniques and then sequenced by Sanger sequencing reactions.
• This sequence was then compared with partial sequences of several other species, including S. muris, S. gigantea, S. tenella, S. cruzi, S. arieticanis, S. capracanis, Toxoplasma gondii, Eimeria tenella, and Cryptosporidium parvum.
• The researchers performed alignments of available sites for all 10 species, and then analyzed these alignments using maximum parsimony and maximum likelihood methods to determine the relative phylogeny, or evolutionary history, of these organisms.

Results and Implications

• The analyses confirmed the placement of S. neurona in the genus Sarcocystis and suggested a close relationship to S. muris, S. gigantea, and T. gondii.
• The molecular phylogeny indicates that Sarcocystis species that utilize the dog (Canis familiaris) as the definitive host evolved from a common ancestor.
• Those species that utilize the cat (Felis domesticus) as the definitive host, including T. gondii, seem to have evolved from another common ancestor.
• Understanding these relationships and possible common ancestors can provide insights into the possible definitive host for S. neurona, which is currently unknown. This could assist in developing strategies for their control and eradication, and contribute to better treatments for the diseases they cause.