Inoculation of Sarcocystis neurona merozoites into the central nervous system of horses.

This research explores the effect of directly injecting Sarcocystis neurona merozoites (a parasite life stage) into the central nervous system of horses, examining its potential as a model for equine protozoal myeloencephalitis (EPM). The findings show that while the horses developed antibodies to S. neurona, they did not present any clinical disease or visible lesions.

Objectives and Rationale of the Study

• The study aimed to establish a horse model for equine protozoal myeloencephalitis (EPM), a neurological condition commonly caused by the parasite Sarcocystis neurona.
• An effective model is needed to examine the efficacy of potential vaccines and drugs for EPM.

Methods and Experimental Design

• Five horses, which previously tested negative for S. neurona antibodies in their serum and cerebrospinal fluid (CSF), were selected for the experiment.
• These horses were injected in the subarachnoid space (a compartment of the brain) with living merozoites (a parasite life cycle stage) of S. neurona’s SN2 isolate.
• The horses were then observed for a period of 132 days.

Findings and Conclusion

• None of the horses developed any clinical signs of disease or died during the observation period. Instead, they all developed antibodies to S. neurona in their CSF and serum about 3-4 weeks post-injection.
• Post-mortem examinations of two horses revealed no parasite-induced lesions in their tissues, and no parasites were found in samples of their spinal cords cultured in a lab.
• The study concluded that while S. neurona merozoites can trigger an immune response (seroconversion), they do not lead to clinical disease when directly injected into the central nervous system of nonimmune horses.