Are Sarcocystis neurona and Sarcocystis falcatula synonymous? A horse infection challenge.

This research investigates whether two different species of protozoan parasites (Sarcocystis neurona and Sarcocystis falcatula) are actually the same species. By administering S. falcatula to horses, the researchers found that it did not cause signs of infection, suggesting that the two species are indeed distinct.

Study Purpose and Design

• The study aimed to test the hypothesis that the two parasites, Sarcocystis neurona and Sarcocystis falcatula are identical, or synonymous. This is notable because S. neurona is known to cause a serious horse disease called Equine protozoal myeloencephalitis (EPM).
• To test this, muscles containing S. falcatula sarcocysts were fed to opossums (Didelphis virginiana). Later, five horses were given S. falcatula sporocysts collected from these laboratory opossums.
• Ten horses in total were used in the study. They were tested extensively to ensure they hadn’t been previously exposed to S. neurona and were kept in a controlled environment for 14 days before the experiment.

Results and Observations

• Over 12 weeks, four out of the five challenged horses showed no clinical signs of infection and no trace of S. neurona antibody or DNA in their blood or cerebrospinal fluid.
• Even after a second exposure, these four horses still showed no signs of infection.
• One horse did develop EPM, but the presence of S. neurona antibodies before the test indicated that the infection had occurred before the sporocyst administration.
• The viability of the S. falcatula sporocysts was confirmed in an in-vitro setting with equine bile and by successfully infecting naive brown-headed cowbirds.

Conclusion and Implications

• The results suggested that S. falcatula and S. neurona are not synonymous due to the apparent inability of S. falcatula to infect horses, unlike S. neurona.
• This discovery is vital as it helps clarify the different roles these two parasites play in the disease ecology and could aid in the development of more effective preventions or treatments for diseases caused by these parasites.