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Author ORCID Identifier

https://orcid.org/0009-0008-9448-198X

Date Available

7-28-2026

Year of Publication

2026

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College

Agriculture, Food and Environment

Department/School/Program

Veterinary Science

Faculty

Daniel K. Howe

Faculty

Theodore Kalbfleisch

Abstract

Equine protozoal myeloencephalitis (EPM) is a neurologic disease of horses prevalent in the Americas, caused by the coccidian parasites Sarcocystis neurona and Neospora hughesi. Toxoplasma gondii is a related parasite that infects nearly all warm-blooded animals, including horses. Prior studies show conflicting results on whether T. gondii contributes to EPM, in part because no validated T. gondii serologic assay exists in horses. This study developed a recombinant TgSAG1 ELISA and confirmatory Western blot. These assays evaluated T. gondii seropositivity in 789 serum samples from healthy and neurologic horses across multiple geographic regions and examined 31 paired serum:CSF samples for evidence of intrathecal antibody production. The rTgSAG1 ELISA showed poor agreement with the Western blot at all cutoffs, possibly due to a weak, inconsistent T. gondii antibody response versus an assay defect. Despite this limitation, one paired sample had a serum:CSF titer ratio below the threshold indicating intrathecal antibody production. However, follow-up Western blots did not corroborate this result, consistent with the ELISA’s overall poor agreement with Western blot. Collectively, the findings did not support the possibility that T. gondii plays a major role in EPM. A reliable, validated serologic assay is needed before the parasite’s contribution can be ruled out.

Keywords: Equine protozoal myeloencephalitis (EPM), Toxoplasma gondii, serology, horses, diagnostics, ELISA

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2026.367

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