Indirect fluorescent antibody test and surface antigen ELISAs for antemortem diagnosis of equine protozoal myeloencephalitis.

BACKGROUND: Recent research suggests that serum : CSF titer ratios could provide the most accurate antemortem diagnosis of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona.
OBJECTIVES: 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. ANIMALS: 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.
METHODS: For each test, descriptive statistics were calculated using serum results alone, CSF results alone, and a serum : CSF titer ratio.
RESULTS: 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.