Evidence of intrathecally-derived antibodies against Toxoplasma gondii in horses suspected of neurological disease consistent with equine protozoal myeloencephalitis.
Abstract: Among the recognized neurologic diseases in horses, equine protozoal myeloencephalitis (EPM) has been reported around the world and still presents challenges in diagnosis and treatment. Horses can present with clinical neurologic signs consistent with EPM while testing negative for the two main causative agents, Sarcocystis neurona or Neospora hughesi, and may still be clinically responsive to anti-parasitic drug therapy. This context led to our hypothesis that another protozoal parasite, Toxoplasma gondii, which is known to cause toxoplasmosis in other mammalian species, is a potential pathogen to cause neurologic disease in horses. To evaluate this hypothesis, serum and cerebrospinal fluid (CSF) were collected from 210 horses presenting with clinical signs compatible with EPM, and the indirect immunofluorescent antibody test (IFAT) was used to detect antibody titers for T. gondii, S. neurona, and N. hughesi. Additionally, the serum to CSF titer ratio was calculated for T. gondii, S. neurona, and N. hughesi infections, suggesting intrathecally-derived antibodies for each of the three agents if the serum:CSF ratio was ≤ 64. There were 133 (63.3%) horses positive for serum T. gondii antibodies using a cutoff titer of 160, and 31 (14.8%) positive for CSF T. gondii antibodies using a cutoff titer of 5. Overall, 21 (10.0%) of EPM-suspect horses had a serum:CSF ratio ≤ 64 for antibodies for T. gondii, while 43 (20.5%) and 8 (3.8%) horses had a serum to CSF ratio ≤ 64 for antibodies for S. neurona and N. hughesi, respectively. A total of 6 (2.9%) animals presented evidence of concurrent intrathecally-derived antibodies for T. gondii and at least one other apicomplexan parasite in this study. Signalment and clinical signs were not different across the groups aforementioned. These data provide evidence of intrathecal production of anti-T. gondii antibodies, indicative of T. gondii infection in the brain and/or spinal cord of horses with EPM-like disease.
Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.
Publication Date: 2023-03-29 PubMed ID: 37043865DOI: 10.1016/j.vetpar.2023.109919Google Scholar: Lookup
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- Journal Article
- Antibodies
- Cerebrospinal Fluid
- Clinical Signs
- Diagnosis
- Disease Diagnosis
- Disease Treatment
- Epidemiology
- Equine Health
- Equine Protozoal Myeloencephalitis
- Horses
- Immunofluorescence Assay
- Immunology
- Infectious Disease
- Neurological Diseases
- Pathogens
- Protozoa
- Sarcocystis
- Serum
- Toxins
- Veterinary Medicine
- Veterinary Research
Summary
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The research investigates the possibility that the protozoal parasite, Toxoplasma gondii, may be a cause of neurological disease in horses, similar to equine protozoal myeloencephalitis (EPM). Through testing, the study finds evidence that antibodies against this parasite can be detected in a significant number of horses presenting with EPM-like symptoms.
Background and Hypothesis
- Equine protozoal myeloencephalitis (EPM) is a known neurological disease in horses, but its diagnosis and treatment can be challenging.
- Some horses present with EPM symptoms but test negative for Sarcocystis neurona or Neospora hughesi, the main causative agents, yet still respond to anti-parasitic drug treatment.
- This situation led to the hypothesis that another protozoal parasite, Toxoplasma gondii, which causes toxoplasmosis in other mammals, might also cause neurological disease in horses.
Research Methodology and Testing
- Serum and cerebrospinal fluid (CSF) were collected from 210 horses exhibiting EPM symptoms.
- The indirect immunofluorescent antibody test (IFAT) was utilized to detect antibody levels for T. gondii, S. neurona, and N. hughesi.
- A ratio of serum to CSF titer was calculated for each infection. A serum:CSF ratio of ≤ 64 suggested intrathecally-derived antibodies for each of the three agents.
Results
- Out of the tested horses, 63.3% were positive for serum T. gondii antibodies, and 14.8% were positive for CSF T. gondii antibodies.
- 10.0% of EPM-suspect horses had a serum:CSF ratio ≤ 64 for antibodies for T. gondii.
- 20.5% and 3.8% of horses had a serum to CSF ratio ≤ 64 for antibodies for S. neurona and N. hughesi, respectively.
- 2.9% of the animals showed evidence of parallel intrathecally-derived antibodies for T. gondii and at least one other apicomplexan parasite.
- No major differences in signalment and clinical signs were observed across the groups.
Conclusion
- The study finds evidence of intrathecally-produced anti-T. gondii antibodies, indicating T. gondii infection in the brain and/or spinal cord of horses with EPM-like disease.
- This suggests T. gondii may be a potential pathogen responsible for neurological diseases in horses.
Cite This Article
APA
Bernardino PN, Pusterla N, Conrad PA, Packham AE, Tamez-Trevino E, Aleman M, James K, Smith WA.
(2023).
Evidence of intrathecally-derived antibodies against Toxoplasma gondii in horses suspected of neurological disease consistent with equine protozoal myeloencephalitis.
Vet Parasitol, 318, 109919.
https://doi.org/10.1016/j.vetpar.2023.109919 Publication
Researcher Affiliations
- Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
- Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
- Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
- Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
- William R. Pritchard Veterinary Medicine Teaching Hospital, Immunology/Virology Laboratory, 1 Garrod Drive, Davis, CA 95616, USA.
- Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
- Department of Obstetrics, Gynecology and Reproductive Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
- Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, 1 Shields Avenue, Davis, CA 95616, USA. Electronic address: wasmith@ucdavis.edu.
MeSH Terms
- Horses
- Animals
- Sarcocystosis / veterinary
- Sarcocystosis / parasitology
- Toxoplasma
- Antibodies, Protozoan
- Horse Diseases / diagnosis
- Sarcocystis
- Encephalomyelitis / veterinary
- Encephalomyelitis / parasitology
- Mammals
Conflict of Interest Statement
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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