• Open Access

Indirect Fluorescent Antibody Test and Surface Antigen ELISAs for Antemortem Diagnosis of Equine Protozoal Myeloencephalitis


  • Cases were evaluated and samples were collected at New Bolton Center. IFAT was performed commercially at UC Davis School of Veterinary Medicine. SAG2, 4/3 ELISA was performed at Equine Diagnostic Solutions, LLC.
  • This study was presented during the EPM SIG meeting at the 2012 ACVIM Forum, New Orleans, LA

Corresponding author: A.L. Johnson, Department of Clinical Studies – New Bolton Center, University of Pennsylvania School of Veterinary Medicine, 382 W. Street Road, Kennett Square, PA 19348; e-mail: amyjohn@vet.upenn.edu.



Recent research suggests that serum : CSF titer ratios could provide the most accurate antemortem diagnosis of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona.


The purpose of this study was to assess the utility of two commercially available tests, the indirect fluorescent antibody test (IFAT) and the surface antigen 2, 4/3 ELISA (SAG2, 4/3 ELISA), using archived paired serum and CSF samples.


Samples were obtained from 4 types of clinical patients. Confirmed positive cases (n = 9 horses; 11 sample sets) had neurologic deficits and postmortem lesions consistent with EPM. Confirmed negative cases (n = 28) had variable clinical signs and postmortem lesions consistent with another disease. Suspected positive cases (n = 6) had neurologic deficits consistent with EPM, marked improvement after treatment, and exclusion of other diseases. Suspected negative cases (n = 14) had variable signs with a strong presumptive diagnosis of another disease.


For each test, descriptive statistics were calculated using serum results alone, CSF results alone, and a serum : CSF titer ratio.


Overall accuracy was highest for SAG2, 4/3 ELISA titer ratio at 0.97 (95% CI 0.88–0.99) with sensitivity = 0.88 (95% CI 0.66–0.97) and specificity = 1 (95% CI 0.92–1). IFAT CSF and titer ratio results also showed high accuracy at 0.88 (95% CI 0.77–0.94), but lower sensitivity = 0.65 (95% CI 0.41–0.83).

Conclusions and Clinical Importance

Using serum results alone was least accurate for both test types. The more accurate methods, such as the SAG2, 4/3 ELISA serum : CSF titer ratio, should be utilized.