Antibody index and specific antibody quotient in horses after intragastric administration of Sarcocystis neurona sporocysts.

This study examines the use of an antibody index for detecting antibodies from Sarcocystis neurona (a parasite) in horses’ brain fluid, after they’re fed with the parasite’s spores. However, the study found that these antibodies seemed to come from outside the brain, indicating that this method may not reliably show infection in the brain.

Objective and Methodology

• The aim of this study was to evaluate the use of a Specific Antibody Index (AI) which compares the quotient (relative amount) of Sarcocystis neurona-specific Immunoglobulin G (IgG) to the total IgG for identifying an anti-S. neurona antibody fraction originating from the central nervous system (CNS) in cerebrospinal fluid (CSF) samples from horses that have ingested S. neurona spores.
• Eighteen adult horses were involved in the study. Fourteen of them were inoculated intragastrically with the S. neurona spores while the remaining four horses were not challenged and served as the control group. Sequential blood and CSF samples were obtained from all horses before and after the administration of the spores.
• Concentrations of S. neurona-specific IgG in both the CSF and the plasma of the horses were measured using an Enzyme-Linked Immunosorbent Assay (ELISA) method. Total IgG concentrations in both the CSF and plasma were also quantified, from which the quotients and the AI were calculated.

Findings and Conclusions

• Findings of the study showed a significant increase in S. neurona-specific IgG detected in CSF samples from horses challenged with the spores.
• However, the study concluded that, even though there was a significant increase in the amount of S. neurona-specific IgG in CSF samples, the antibodies appeared to be extraneural in origin, meaning that they did not originate from the CNS, therefore implying that the ingestion of spores may not result in a reliable infection of the CNS in the horses.
• Despite these findings, the authors still suggest that calculation of a specific AI may be useful in the diagnosis of S. neurona-associated myeloencephalitis (inflammation of the brain and spinal cord) in horses. Therefore, further studies are needed to conclusively verify the efficacy of this diagnostic approach.