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


OBJECTIVE
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.


METHODS
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
Low sensitivity of the SAG-1 ELISA limited its usefulness for antemortem diagnosis of EPM in this patient population.
Johnson
A L
AL
Department of Clinical Studies, New Bolton Center, University of Pennsylvania School of Veterinary Medicine, Kennett Square, PA, USA. amyjohn@vet.upenn.edu
Burton
A J
AJ
Sweeney
R W
RW
D000818:Animals; D004679:Encephalomyelitis / Q000175:diagnosis / Q000469:parasitology / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods / Q000662:veterinary*; D006734:Horse Diseases / Q000175:diagnosis* / Q000276:immunology / Q000469:parasitology; D006736:Horses; D012189:Retrospective Studies; D012522:Sarcocystis / Q000276:immunology*; D012523:Sarcocystosis / Q000175:diagnosis / Q000662:veterinary*; D012680:Sensitivity and Specificity