Equine protozoal myeloencephalitis (EPM) is a serious neurologic disease of horses caused primarily by the protozoal parasite Sarcocystis neurona. The parasite causes asymmetric neurologic deficits in horses in both North and South America. EPM has a significant economic impact on the US horse industry, with estimated costs from $55.4 to $110.8 million per year.
Currently, antemortem testing is limited in its specificity in exposed and diseased horses. This paper reports on the development of an IgM capture enzyme linked immunoassay (ELISA) for the identification of acute infection with S. neurona. The ELISA was based on the S. neurona low molecular weight protein SNUCD-1 antigen and the monoclonal antibody 2G5 labeled with horseradish peroxidase. The test was evaluated using serum and CSF from 12 horses experimentally infected with 1.5 million S. neurona sporocysts and 16 horses experimentally infected with varying doses (100 to 100,000) of S. neurona sporocysts, all of whose histopathology results were available.
The hypothesis of this study was that serum and cerebrospinal fluid (CSF) of horses experimentally challenged with S. neurona would have an increased S. neurona-specific IgM (Sn-IgM) concentration relative to their pre-infected state. For horses challenged with 1.5 million sporocysts, the results indicate a significant increase in serum Sn-IgM concentrations relative to pre-inoculation for weeks 2 through 6 post-inoculation.
For horses inoculated with lower doses of S. neurona, there were significant increases in Sn-IgM concentration at various points in time depending on the inoculation dose. Finally, there was a significant increase between the pre- and post-inoculation CSF Sn-IgM concentrations. Our results support the assay as a valuable addition as a diagnostic tool during the acute phase of EPM.