SarcoFluor antibody test for the detection of specific antibodies to Sarcocystis

Using a combined serum and CSF antibody test and comparing the comparative levels can give you a 90% chance of detecting an EPM infection.
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A fresh look at the SarcoFluor antibody test for the detection of specific antibodies to Sarcocystis neurona for the diagnosis of equine protozoal myeloencephalitis
Vet Parasitol. 2024 Jun 3:330:110219. doi: 10.1016/j.vetpar.2024.110219. Online ahead of print.
Authors
Pranav S Pandit 1 , Woutrina A Smith 2 , Carrie J Finno 3 , Monica Aleman 4 , Patricia A Conrad 5 , Andrea Packham 2 , Magdalena Plancarte 2 , Kevin Woolard 5 , Antoinette Marsh 6 , Nicola Pusterla 4
Affiliations

1 Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, One Shields Avenue, Davis, CA 95616, USA. Electronic address: pspandit@ucdavis.edu.
2 One Health Institute, School of Veterinary Medicine, University of California, 1089 Veterinary Medicine Drive, VM3B, Davis, CA 95616, USA.
3 Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, One Shields Avenue, Davis, CA 95616, USA.
4 Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, Tupper Hall 2108, One Shields Avenue, Davis, CA 95616, USA.
5 Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA, 95616, USA.
6 Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, 1920 Coffey Road, Columbus, OH, USA.

PMID: 38897057
DOI: 10.1016/j.vetpar.2024.110219

Abstract

Equine protozoal myeloencephalitis (EPM) is a challenging disease to diagnose in horses with neurological signs. To optimize contemporary diagnostic testing, including the use of serum:CSF antibody ratios, the SarcoFluor antibody test for Sarcocystis neurona requires revalidation. The SarcoFluor, a previously validated immunofluorescent antibody test (IFAT) for the detection of antibodies specific to S. neurona in serum and cerebrospinal fluid (CSF) of naturally infected horses was analyzed using recent data and considering a serum:CSF antibody ratio threshold. Utilization of serum and CSF phosphorylated neurofilament heavy protein (pNfH) concentrations in support of an EPM diagnosis was also evaluated. 172 horses were divided into three groups: EPM-positive horses (EPM+, n=42), neurological non-EPM horses (n=74) confirmed with non-EPM neurological diseases (cervical vertebral compressive myelopathy, equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy), and control horses (control, n=56) without neurological signs and neurological abnormalities on histology. Logistic regression was used to compare EPM diagnostic regimens. Specifically, EPM+ horses were compared with neurological non-EPM horses showing neurological signs. To consider diagnostic utility, post-test probabilities were calculated by titer. When differentiating between EPM and other neurological diseases, the combination of serum and CSF SarcoFluor testing added more information to the model accuracy than either test alone. Using serum and CSF for pNfH in support of an EPM diagnosis did not identify cutoffs with statistically significant odds ratios but increased the overall model accuracy when used with the IFAT. Utilization of IFAT titers against S. neurona in serum and CSF result in a high post-test probability of detecting EPM+ horses in a clinical setting.

Keywords: Diagnostic test evaluation; Neurologic diseases; Serology.

Copyright © 2024. Published by Elsevier B.V.