Evidence to support horses as natural intermediate hosts for Sarcocystis neurona.
Abstract: Opossums (Didelphis spp.) are the definitive host for the protozoan parasite Sarcocystis neurona, the causative agent of equine protozoal myeloencephalitis (EPM). Opossums shed sporocysts in feces that can be ingested by true intermediate hosts (cats, raccoons, skunks, armadillos and sea otters). Horses acquire the parasite by ingestion of feed or water contaminated by opossum feces. However, horses have been classified as aberrant intermediate hosts because the terminal asexual sarcocyst stage that is required for transmission to the definitive host has not been found in their tissues despite extensive efforts to search for them [Dubey, J.P., Lindsay, D.S., Saville, W.J., Reed, S.M., Granstrom, D.E., Speer, C.A., 2001b. A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM). Vet. Parasitol. 95, 89-131]. In a 4-month-old filly with neurological disease consistent with EPM, we demonstrate schizonts in the brain and spinal cord and mature sarcocysts in the tongue and skeletal muscle, both with genetic and morphological characteristics of S. neurona. The histological and electron microscopic morphology of the schizonts and sarcocysts were identical to published features of S. neurona [Stanek, J.F., Dubey, J.P., Oglesbee, M.J., Reed, S.M., Lindsay, D.S., Capitini, L.A., Njoku, C.J., Vittitow, K.L., Saville, W.J., 2002. Life cycle of Sarcocystis neurona in its natural intermediate host, the raccoon, Procyon lotor. J. Parasitol. 88, 1151-1158]. DNA from schizonts and sarcocysts from this horse produced Sarcocystis specific 334bp PCR products [Tanhauser, S.M., Yowell, C.A., Cutler, T.J., Greiner, E.C., MacKay, R.J., Dame, J.B., 1999. Multiple DNA markers differentiate Sarcocystis neurona and Sarcocystis falcatula. J. Parasitol. 85, 221-228]. Restriction fragment length polymorphism (RFLP) analysis of these PCR products showed banding patterns characteristic of S. neurona. Sequencing, alignment and comparison of both schizont and sarcocyst DNA amplicons showed 100% identity. Although Koch's postulates have not been demonstrated in this case study, the finding of mature, intact S. neurona schizonts and sarcocysts in the tissues of this single horse strongly suggests that horses have the potential to act as intermediate hosts. Further studies are needed to demonstrate Koch's postulates with repeated transfer of S. neurona between opossums and horses.
Publication Date: 2005-06-23 PubMed ID: 15970386DOI: 10.1016/j.vetpar.2005.05.016Google Scholar: Lookup
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Summary
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This research paper focuses on presenting evidence that horses can act as natural intermediate hosts for Sarcocystis neurona, the parasite responsible for a neurological disease in horses, called equine protozoal myeloencephalitis. Previously, horses were only known to pick up the parasite from contaminated feed, and were thought incapable of transmitting the parasite to definitive hosts, like opossums.
Objective of the Research
- The main goal of this research was to determine if horses could harbour the asexual stage of Sarcocystis neurona and therefore act as an intermediate host and not just as an aberrant host.
Methodology
- The scientists studied a 4-month-old filly with neurological symptoms consistent with equine protozoal myeloencephalitis.
- In this horse, they identified and studied structures known as schizonts in the brain and spinal cord, and mature sarcocysts in the tongue and skeletal muscle.
- The morphology of the parasites was analysed through histological and electron microscopic examinations.
- DNA from these parasites was also extracted and studied using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) techniques.
Findings
- Both the schizonts and sarcocysts that were identified in the horse matched the morphological characteristics of S. neurona as documented in previous research.
- The DNA analysis further confirmed the identity of the schizonts and sarcocysts as S. neurona, with the PCR products showing band patterns typical of S. neurona, and the extracted DNA sequences matching 100% with the S. neurona reference sequence.
Implications and Future Research
- The findings of this study suggest that horses can act as natural intermediate hosts for S. neurona. This is a significant step in understanding the parasite’s life cycle and how it is transmitted.
- This can potentially change our understanding of the parasitic disease in horses and might necessitate changes in prevention and treatment methods.
- However, the authors note that Koch’s postulates, which are a series of criteria designed to establish a causative relationship between a microbe and a disease, have not been fulfilled in this study. Fulfilling Koch’s postulates would require showing a repeated transfer of S. neurona between opossums and horses and observing consistent disease development.
- Therefore, further studies are necessary to definitively determine whether horses can function as intermediate hosts for S. neurona.
Cite This Article
APA
Mullaney T, Murphy AJ, Kiupel M, Bell JA, Rossano MG, Mansfield LS.
(2005).
Evidence to support horses as natural intermediate hosts for Sarcocystis neurona.
Vet Parasitol, 133(1), 27-36.
https://doi.org/10.1016/j.vetpar.2005.05.016 Publication
Researcher Affiliations
- Diagnostic Center for Population and Animal Health (DCPAH), College of Veterinary Medicine, Michigan State University (MSU), East Lansing, MI 48824, USA.
MeSH Terms
- Animals
- Base Sequence
- DNA, Protozoan / chemistry
- DNA, Protozoan / genetics
- Encephalomyelitis / parasitology
- Encephalomyelitis / pathology
- Encephalomyelitis / veterinary
- Fatal Outcome
- Female
- Horse Diseases / parasitology
- Horse Diseases / pathology
- Horses
- Immunohistochemistry / veterinary
- Microscopy, Electron, Transmission / veterinary
- Molecular Sequence Data
- Polymerase Chain Reaction / veterinary
- Polymorphism, Restriction Fragment Length
- Sarcocystis / genetics
- Sarcocystis / isolation & purification
- Sarcocystis / ultrastructure
- Sarcocystosis / parasitology
- Sarcocystosis / pathology
- Sarcocystosis / veterinary
- Sequence Alignment
Citations
This article has been cited 8 times.- O'Byrne AM, Lambourn DM, Rejmanek D, Haman K, O'Byrne M, VanWormer E, Shapiro K. Sarcocystis neurona Transmission from Opossums to Marine Mammals in the Pacific Northwest.. Ecohealth 2021 Mar;18(1):84-94.
- Reed SM, Furr M, Howe DK, Johnson AL, MacKay RJ, Morrow JK, Pusterla N, Witonsky S. Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention.. J Vet Intern Med 2016 Mar-Apr;30(2):491-502.
- Dubey JP, Howe DK, Furr M, Saville WJ, Marsh AE, Reed SM, Grigg ME. An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM).. Vet Parasitol 2015 Apr 15;209(1-2):1-42.
- Awinda PO, Mealey RH, Williams LB, Conrad PA, Packham AE, Reif KE, Grause JF, Pelzel-McCluskey AM, Chung C, Bastos RG, Kappmeyer LS, Howe DK, Ness SL, Knowles DP, Ueti MW. Serum antibodies from a subset of horses positive for Babesia caballi by competitive enzyme-linked immunosorbent assay demonstrate a protein recognition pattern that is not consistent with infection.. Clin Vaccine Immunol 2013 Nov;20(11):1752-7.
- Kutkiene L, Prakas P, Sruoga A, Butkauskas D. The mallard duck (Anas platyrhynchos) as intermediate host for Sarcocystis wobeseri sp. nov. from the barnacle goose (Branta leucopsis).. Parasitol Res 2010 Sep;107(4):879-88.
- Miller MA, Barr BC, Nordhausen R, James ER, Magargal SL, Murray M, Conrad PA, Toy-Choutka S, Jessup DA, Grigg ME. Ultrastructural and molecular confirmation of the development of Sarcocystis neurona tissue cysts in the central nervous system of southern sea otters (Enhydra lutris nereis).. Int J Parasitol 2009 Oct;39(12):1363-72.
- Dahlgren SS, Gjerde B. Sarcocystis in moose (Alces alces): molecular identification and phylogeny of six Sarcocystis species in moose, and a morphological description of three new species.. Parasitol Res 2008 Jun;103(1):93-110.
- Elsheikha HM, Schott HC 2nd, Mansfield LS. Genetic variation among isolates of Sarcocystis neurona, the agent of protozoal myeloencephalitis, as revealed by amplified fragment length polymorphism markers.. Infect Immun 2006 Jun;74(6):3448-54.
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