Equine protozoal Myeloencephalitis (EPM) is a neurologic disease in horses predominantly caused by the protozoa Sarcocystis neurona. Carried by the North American opossum, Didelphis virginiana, horses are exposed to S. neurona when eating or drinking food or water contaminated with opossum feces. While exposure to the protozoa is high, only around 1% of horses develop clinical disease. While the mechanism by which S. neurona causes central nervous system damage is still unknown, this dissertation examines the histopathologic damage and potential persistence of S. neurona after anti-protozoal treatment between groups of horses with acute and chronic disease. This dissertation also examines the ability of two diagnostic techniques, immunohistochemistry (IHC) and polymerase chain reaction (PCR), to detect S. neurona. Horses were grouped based on duration of clinical signs; acutely affected horses exhibited clinical signs <6 months, while chronically affected horses exhibited clinical signs >6 months, including those previously treated for EPM. A comparison of necropsy reports revealed that chronically affected horses with EPM had more degenerative changes compared to acutely affected horses with EPM. However, when histologic changes were quantified, acutely affected horses had similar degenerative changes compared to chronically affected horses. When IHC and PCR were compared, IHC detected S. neurona presence (9/9 horses with EPM) significantly more often than PCR 4/9 horses with EPM). Our studies also show that S. neurona can be persistent in horses, as evidenced by the detection of S. neurona in the CNS of horses previously treated for EPM. Four horses had previously been treated for EPM, and all four had S. neurona present in their CNS even after anti-protozoal treatment, suggesting the ability for S. neurona to persist. In addition, this dissertation examines the possibility of using soluble CD14 (sCD14) as a supplemental assay for differentiating neurologic diseases such as EPM and cervical vertebral stenotic myelopathy (CVSM). When sCD14 levels were assessed in control EPM, CVSM, and EPM+CVSM horses, sCD14 concentrations in the cerebral spinal fluid (CSF) were significantly different between control and EPM horses and EPM horses and CVSM horses. With this information, clinicians and researchers may use sCD14 as a supplemental assay for differentiating between healthy, EPM, and CVSM horses. Finally, future directions include preliminary data that may lead to a potential for a peptide vaccine protecting horses from EPM clinical disease. Further insight into the persistence of S. neurona after anti-protozoal treatment is needed, the classification of acutely and chronically affected horses and the ability of sCD14 detection as a supplemental assay will be required; this this dissertation allows for the continuation of knowledge in combating the elusive protozoa, S. neurona. / Doctor of Philosophy / Equine protozoal myeloencephalitis (EPM) is a common neurologic disease in horses in North and South America caused predominantly by the parasite Sarcocystis neurona. This disease is carried by the North American opossum (Didelphis virginiana), and horses encounter S. neurona when eating or drinking food or water contaminated with opossum feces. Not all horses who encounter the parasite develop disease and can clear the parasite before disease occurs. One study in this dissertation found that the immunohistochemistry (IHC) test was significantly better at detecting S. neurona than polymerase chain reaction (PCR). Additionally, horses with EPM were broken into two groups: acutely affected horses with neurologic signs <6 months and chronically affected horses with neurologic signs >6 months. The study found that horses chronically afflicted with EPM had more degenerative changes compared to acutely affected horses. In addition, four horses who had previously been treated for EPM had S. neurona in their central nervous system (CNS), suggesting the ability of the parasite to persist after EPM treatment and that persistence of S. neurona may cause greater degenerative changes in horses with long-term neurological signs. The final study in this dissertation examined the potential for an assay to be used to help differentiate EPM from other neurologic diseases such as cervical vertebral stenotic myelopathy (CVSM). By measuring sCD14 concentration in the serum and cerebral spinal fluid (CSF) of control, EPM horses, CVSM horses, and EPM+CVSM horses, significant differences were found between control and EPM horses, and EPM and CVSM horses. This finding indicates the potential for sCD14 to be used to help differentiate between these two devastating neurologic diseases. The future directions include preliminary data that could lead for a potential protein vaccine capable of protecting horses from EPM disease. Overall, the results of these studies improve our knowledge of EPM and potentially improve equine health worldwide.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119311 |
| Date | 05 June 2024 |
| Creators | Helber, Lauren Anne |
| Contributors | Biomedical and Veterinary Sciences, Witonsky, Sharon G., Ramirez Barrios, Roger Antonio, LeRoith, Tanya, Zimmerman, Kurt L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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