Funds provided by the Center for Equine Health and the Wayne and Gladys Valley Foundation

Patricia A. Conrad,
Bradd C. Barr,
Ian A. Gardner,
W. David Wilson,
Barbara Daft,
Antoinette E. Marsh,
Andrea E. Packham,
Karen W. Sverlow

Description of the Problem: The diagnosis of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona is often confusing and inconclusive. The most widely used diagnostic test for EPM is the Western blot (immunoblot) assay. This assay is highly sensitive but only moderately specific, and the test results are difficult to interpret and reproduce. To further complicate diagnosis, a new protozoan, Neospora hughesi, was recently identified as another cause of EPM. Veterinarians need improved testing methods to diagnose EPM.

Study Objectives: Long-term -- determine if S. neurona and N. hughesi infections can be distinguished and better diagnosed using newly developed antibody tests. Specifically: 1) complete the development of modified agglutination tests (MAT) to detect equine antibodies to Sarcocystis neurona and Neospora hughesi (year 1), 2) develop enzyme-linked immunosorbent assays (ELISAs) that utilize whole parasite or recombinant antigens for N. hughesi (year 1), and 3) compare the sensitivity and specificity of the indirect fluorescent antibody test (IFAT), MAT, recombinant antigen ELISA, whole parasite ELISA and Western blot assay developed for each parasite using a "gold standard" panel of equine serum and CSF (year 2).

Experimental Approach: Researchers will develop new tests for S. neurona and N. hughesi which should have advantages over the present immunoblot assay. These tests will be compared to existing tests for each parasite using a "gold standard" panel of equine serum (blood) and CSF (cerebral spinal fluid). This panel will include samples from confirmed clinical cases, experimentally infected horses and clinically normal horses, all of which have EPM lesions and parasites in their brains and/or spinal cords. Based on this comparative evaluation, researchers can recommend the best test(s) for use in diagnosing EPM and for use in important field studies to investigate how horses acquire these infections.

Anticipated Benefits to the Equine Industry: EPM is a disease of major concern and economic importance to the equine industry. The long-term goal is to improve the diagnosis, prevention and control of EPM. This study will ensure the development of five different antibody detection tests specifically for the EPM-causing parasites. By comparing these tests, researchers will be able to select the most sensitive and specific test(s) which can be used for EPM diagnosis and epidemiological studies.

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Reprinted with permission of the copyright holder and the Center For Equine Health. The materials offered in this article are intended for educational purposes only. Always consult your veterinarian in matters regarding the health of your animals.

The research conducted by the UC Davis Center for Equine Health is supported with funds provided by the Oak Tree Racing Association, the State of California pari-mutuel fund, and contributions by private donors. Please visit The UC Davis Center For Equine Health website for addtional information at http://www.vetmed.ucdavis.edu/ceh

The Horse Report: Writer/Editor: Laurie FioEditor/WriterCenter for Equine HealthSchool of Veterinary MedicineUniversity of CaliforniaOne Shields AvenueDavis, CA 95616-8589phone: (530) 752-4434fax: (530) 752-9379e-mail: ltfio@ucdavis.edu