Accurate antemortem diagnosis of equine protozoal myeloencephalitis (EPM) based on detecting intrathecal antibodies against Sarcocystis neurona using the SnSAG2 and SnSAG4/3 ELISAs.

Abstract

BACKGROUND:

Recent work demonstrated the value of antigen-specific antibody indices (AI and C-value) to detect intrathecal antibody production against Sarcocystis neurona for antemortem diagnosis of equine protozoal myeloencephalitis (EPM).

OBJECTIVES:

The study was conducted to assess whether the antigen-specific antibody indices can be reduced to a simple serum : cerebrospinal fluid (CSF) titer ratio to achieve accurate EPM diagnosis.

ANIMALS:

Paired serum and CSF samples from 128 horses diagnosed by postmortem examination. The sample set included 44 EPM cases, 35 cervical-vertebral malformation (CVM) cases, 39 neurologic cases other than EPM or CVM, and 10 non-neurologic cases.

METHODS:

Antibodies against S. neurona were measured in serum and CSF pairs using the SnSAG2 and SnSAG4/3 (SnSAG2, 4/3) ELISAs, and the ratio of each respective serum titer to CSF titer was determined. Likelihood ratios and diagnostic sensitivity and specificity were calculated based on serum titers, CSF titers, and serum : CSF titer ratios.

RESULTS:

Excellent diagnostic sensitivity and specificity was obtained from the SnSAG2, 4/3 serum : CSF titer ratio. Sensitivity and specificity of 93.2 and 81.1%, respectively, were achieved using a ratio cutoff of ≤100, whereas sensitivity and specificity were 86.4 and 95.9%, respectively, if a more rigorous cutoff of ≤50 was used. Antibody titers in CSF also provided good diagnostic accuracy. Serum antibody titers alone yielded much lower sensitivity and specificity.

CONCLUSIONS AND CLINICAL IMPORTANCE:

The study confirms the value of detecting intrathecal antibody production for antemortem diagnosis of EPM, and they further show that the antigen-specific antibody indices can be reduced in practice to a simple serum : CSF titer ratio.

• Authors: S M Reed, D K Howe, J K Morrow, A Graves, M R Yeargan, A L Johnson, R J MacKay, M Furr, W J A Saville, N M Williams
• Journal: Journal of veterinary internal medicine (J Vet Intern Med) 2013 Sep-Oct Vol. 27 Issue 5 Pg. 1193-200 ISSN: 1939-1676 [Electronic] United States
• PMID: 24033423 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2013 by the American College of Veterinary Internal Medicine.

Chemical References

• Antibodies, Protozoan
• Protozoan Proteins

Topics

• Animals
• Antibodies, Protozoan (blood, cerebrospinal fluid)
• Encephalomyelitis (cerebrospinal fluid, parasitology, veterinary)
• Enzyme-Linked Immunosorbent Assay (veterinary)
• Horse Diseases (diagnosis, parasitology)
• Horses
• Predictive Value of Tests
• Protozoan Proteins (cerebrospinal fluid, immunology)
• Sarcocystis (immunology)
• Sarcocystosis (blood, cerebrospinal fluid, parasitology, veterinary)
• Sensitivity and Specificity