Antibody Coefficients for the Diagnosis of Equine Protozoal Myeloencephalitis

Background Diagnosis of equine protozoal myeloencephalitis (EPM) remains a challenge for equine practitioners. Current utilized methods have inadequate sensitivity and specificity, because of a high number of false positive results. Hypothesis/Objective Evaluation of antibody indices to Sarcocystis neurona should provide high sensitivity and specificity for diagnosis of EPM. Animals Archived samples from 29 clinical patients. Methods Archived serum and cerebrospinal fluid (CSF) samples from clinical patients with either EPM (14) or cervical vertebral compressive myelopathy (CVM) (15) were examined and tested for anti-S. neurona antibodies by the SnSAG2 ELISA. The results were used to calculate the antibody index (AI) and C-value. Sensitivity and specificity were calculated, and the AI, C-value, immunoglobulin G (IgG) concentrations, and anti-S. neurona titers compared. In addition, negative CSF was spiked in varying concentrations with blood from a horse with a high anti-S. neurona titer, and the tests repeated. Results Results demonstrated that the IgG concentration, anti-S. neurona titer, AI, and C-value were significantly higher (P < .05) in horses with EPM than in those with CVM. Sensitivity and specificity of the AI was 71 and 100%, respectively, and that of the C-value was 86 and 100%, respectively. In addition, the AI and C-value from the samples spiked with S. neurona positive blood remained below 1 (eg, negative) in CSF with a red blood cell (RBC) count up to 105 RBC/mu L. Conclusions/Clinical Importance Results of the study demonstrate the value of calculating the AI and C-value in the diagnosis of EPM in horses. In addition, the test is robust in the presence of blood contamination.