Evaluation and Comparison of an Indirect Fluorescent Antibody Test for Detection of Antibodies to Sarcocystis Neurona, Using Serum and Cerebrospinal Fluid of Naturally and Experimentally Infected, and Vaccinated Horses

Abstract

The objectives of this study were to evaluate the accuracy of the indirect fluorescent antibody test (IFAT) using serum and cerebrospinal fluid (CSF) of horses naturally and experimentally infected with Sarcocystis neurona, to assess the correlation between serum and CSF titers, and to determine the effect of S. neurona vaccination on the diagnosis of infection. Using receiver-operating characteristic analysis, the areas under the curve for the IFAT were 0.97 (serum) and 0.99 (CSF). Sensitivity and specificity were 83.3 and 96.9% (serum, cutoff 80) and 100 and 99% (CSF, cutoff 5), respectively. Titer-specific likelihood ratios (LRs) ranged from 0.03 to 187.8 for titers between <10 and 640. Median time to conversion was 22-26 days postinfection (DPI) (serum) and 30 DPI (CSF). The correlation between serum and CSF titers was moderately strong (r = 0.6) at 30 DPI. Percentage of vaccinated antibody-positive horses ranged from 0 to 95% between 0 and 112 days after the second vaccination. Thus, the IFAT was reliable and accurate using serum and CSF. Use of LRs potentially improves clinical decision making. Correlation between serum and CSF titers affects the joint accuracy of the IFAT; therefore, the ratio of serum to CSF titers has potential diagnostic value. The S. neurona vaccine could possibly interfere with equine protozoal myeloencephalitis diagnosis.

Indirect Fluorescent Antibody Test and Surface Antigen ELISAs for Antemortem Diagnosis of Equine Protozoal Myeloencephalitis

“…When results of this study are compared with those of previous studies evaluating the IFAT, 1,7,10 IFAT test performance was not as good, with lower sensitivity and specificity estimates regardless of whether serum or CSF was used. This finding was consistent despite the fact that one of the previous studies was performed at the same institution, albeit with different cases.…”

Sarcocystis fayeri in skeletal muscle of horses with neuromuscular disease

“…[20] However, in the present study only 2 horses had serum IFA titers above the cut-off value considered supportive of probability of clinical disease. [33,34] Although there was no apparent age predilection in this study, diseased equids appeared to be mainly young mature horses (median 7, mean 7.9 + 5.6 years) with 83.3% being younger than 15 years of age. This is in contrast to reports of older animals having higher parasite loads.…”

Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention

“…Descriptions of testing options and reported test performance are shown in Table 1 71, 72, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93. All tests can be performed on serum or CSF, and none is considered a gold standard.…”