Accurate antemortem diagnosis of equine protozoal myeloencephalitis (EPM) based on detecting intrathecal antibodies against Sarcocystis neurona using the SnSAG2 and SnSAG4/3 ELISAs.

This research emphasizes the importance of the detection of antibodies against Sarcocystis neurona for the accurate diagnosis of Equine protozoal myeloencephalitis (EPM) prior to death, and suggests a simplified diagnostic process by using a serum to cerebrospinal fluid (CSF) titer ratio instead of complex antibody indices.

Study Objective

The study aimed to validate the practical efficacy of antigen-specific antibody indices for the antemortem diagnosis of EPM in horses, and tested if these indices could be simplified to a serum : CSF titer ratio method that retains the same level of diagnostic accuracy.

Methodology

• The study involved paired serum and CSF samples from 128 horses that were postmortem diagnosed.
• The samples came from a variety of horse disease cases, including 44 EPM cases, 35 cases of cervical-vertebral malformation (CVM), 39 neurological cases unrelated to EPM or CVM, and 10 non-neurological cases.
• The researchers measured antibodies against S. neurona in the serum and CSF pairs using two Enzyme-Linked Immunosorbent Assays (ELISAs), SnSAG2 and SnSAG4/3.
• From these measurements, they determined the ratio of serum antibody titers to CSF titers.
• Diagnostic sensitivity and specificity, as well as likelihood ratios, were calculated based on the serum titers, CSF titers, and serum : CSF titer ratios.

Results

• The results demonstrated that high diagnostic sensitivity and specificity could be achieved using the SnSAG2, 4/3 serum : CSF titer ratio method.
• A sensitivity of 93.2% and specificity of 81.1% were achieved using a ratio cutoff of ≤100, while a sensitivity of 86.4% and specificity of 95.9% were achieved using a more stringent cutoff of ≤50.
• The researchers also found that antibody titers in CSF alone provided good diagnostic accuracy.
• However, the use of serum antibody titers alone yielded much lower sensitivity and specificity.

Conclusion

The research validated the value of detecting intrathecal antibody production for their prior-death diagnosis of EPM, and importantly, demonstrated that the antigen-specific antibody indices process could be simplified in practice to a serum : CSF titer ratio without compromising diagnostic robustness. The findings have important implications for improving the ease and accessibility of EPM diagnostic procedures, potentially leading to earlier diagnosis and treatment in clinical practice.