Comparison of a Serum Indirect Fluorescent Antibody Test with Two Western Blot Tests for the Diagnosis of Equine Protozoal Myeloencephalitis

A serum indirect fluorescent antibody test (IFAT) was compared with a Western blot (WB) and a modified Western blot (mWB) for diagnosis of equine protozoal myeloencephalitis (EPM). Using receiver-operating characteristic (ROC) analysis, the area under the curve of the IFAT was greater than the area under the curves of the WB and the mWB (P = 0.025 and P = 0.044, respectively). There was no statistically significant difference between the areas under the curves of the WBs (P > 0.05). On the basis of an arbitrarily chosen cut-off titer for a positive test result of 1:80 for the IFAT and interpreting weak positive WB results as positive test results, the sensitivities and 95% confidence intervals (CI) of all 3 tests were identical and equal to 88.9% (51.8–99.7%). The specificities and 95% CIs of the IFAT, WB, and mWB test were 100% (91–100%), 87.2% (72.6–95.7%), and 69.2% (52.4–83%), respectively. The overall accuracy of the IFAT was shown to be better than that of the WBs and, therefore, the test has potential for use in the diagnosis of EPM caused by Sarcocystis neurona.