Indirect Fluorescent Antibody Test and Surface Antigen ELISA s 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 S arcocystis 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 ( SAG 2, 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 SAG 2, 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 SAG 2, 4/3 ELISA serum :  CSF titer ratio, should be utilized.