Utility of 2 immunological tests for antemortem diagnosis of equine protozoal myeloencephalitis (Sarcocystis neurona infection) in naturally occurring cases

• Published in: Journal of veterinary internal medicine 2010-09, Vol.24 (5), p.1184-1189
• Main Authors: Johnson, A.L, Burton, A.J, Sweeney, R.W
• Format: Article
• Language: English
• Subjects: Animals; antigens; blood serum; cerebrospinal fluid; ELISA; Encephalomyelitis - diagnosis; Encephalomyelitis - parasitology; Encephalomyelitis - veterinary; enzyme-linked immunosorbent assay; Enzyme-Linked Immunosorbent Assay - methods; Enzyme-Linked Immunosorbent Assay - veterinary; equine protozoal myeloencephalitis; fluorescence; Fluorescent Antibody Technique, Indirect - methods; Fluorescent Antibody Technique, Indirect - veterinary; Horse Diseases - diagnosis; Horse Diseases - immunology; Horse Diseases - parasitology; Horses; Indirect fluorescent antibody test; necropsy; Neurologic; orthopedics; patients; Retrospective Studies; Sarcocystis - immunology; Sarcocystis neurona; Sarcocystosis - diagnosis; Sarcocystosis - veterinary; Sensitivity and Specificity; Western blot
• ISSN: 0891-6640; 1939-1676; 1939-1676
• DOI: 10.1111/j.1939-1676.2010.0576.x

Background: Antemortem diagnosis of equine protozoal myeloencephalitis (EPM) is challenging. Limited information is available regarding a commercial test (surface antigen 1 [SAG-1] ELISA). Performance of another commercial test (indirect fluorescent antibody test [IFAT]) using samples from an independent group has not been well described. Hypothesis/Objectives: The primary goal was to evaluate the SAG-1 ELISA and IFAT using naturally occurring EPM cases. A secondary goal was to obtain more information regarding clinical presentation. Animals: Hospital cases were admitted over 20 months and classified into 4 groups. Confirmed positive cases (n = 9) had asymmetric or multifocal neurologic deficits or both and postmortem lesions consistent with EPM. Confirmed negative cases (n = 17) had variable clinical signs and postmortem lesions consistent with another neurologic disease (or no lesions). Suspected positive cases (n = 10) had asymmetric or multifocal deficits or both, marked improvement after treatment for EPM, and other likely diseases excluded. Suspected negative cases (n = 29) had orthopedic disease and no neurologic deficits. Methods: Results of immunological testing (SAG-1 ELISA and IFAT on serum or cerebrospinal fluid [CSF] or both), neurologic examinations, CSF analyses, and postmortem examinations were analyzed retrospectively. Results: SAG-1 ELISA sensitivity was 12.5% (95% CI, 1.6-38.4) and specificity was 97.1% (95% CI, 84.7-99.9) using serum. IFAT sensitivity was 94.4% (95% CI, 72.7-99.9) and specificity was 85.2% (95% CI, 66.3-95.8) using serum; sensitivity was 92.3% (95% CI, 64.0–99.8) and specificity was 89.7% (95% CI, 72.7-97.8) using CSF. Conclusions and Clinical Importance: Low sensitivity of the SAG-1 ELISA limited its usefulness for antemortem diagnosis of EPM in this patient population.