S. neurona antibody prevalence in horses at Morehead State

From Equine Disease Quarterly, Funded by Underwriters at Lloyd's, London, Brokers, and Their Kentucky Agents, http://www.uky.edu/Agriculture/VetScience/q_jan02/q-jan02.htm.

Equine Protozoal Myeloencephalitis (EPM) is an infectious, degenerative protozoal disease of the central nervous system of the horse. The causative agent of EPM has been identified as Sarcocystis neurona.  Dr. David Granstrom developed the first pre-mortem test for the presence of S. neurona antibodies in 1993, using a western blot immunoassay. This test is currently the most reliable test that can be performed on serum and cerebrospinal fluid to detect the presence of antibodies to S. neurona.

The incidence of S. neurona is highest in the eastern U.S. because of the geographic habitat of the opossum, which is the definitive host. When ingested in high enough levels, the parasite can cause a broad range of clinical signs, including weight loss, muscle atrophy of the rear limbs, incoordination, urinary and fecal incontinence, gait abnormalities, paralysis, seizures and death.

The purpose of this research was to establish a base-line antibody level for the Morehead State University equine herd in Morehead, Kentucky. The study involved 39 adult horses (stallions, mares, and geldings) of various breeds, ranging in age from 4 years to 33 years of age. All horses were housed at the Derrickson Agricultural Complex on the Morehead State Farm and were housed and fed in a similar fashion.

In this study, one jugular venipuncture was performed on each horse to obtain a sample of whole blood. Each sample was analyzed at Equine Bio-Diagnostics Laboratories, Lexington, Kentucky by western blot to detect the prevalence of S. neurona antibody in this group. The results of the study demonstrate a high rate of exposure to S. neurona in the herd (32/39) or 82% of the horses sampled (positive, low positive, or weak positive). Forty-four percent (17/39) of horses showed a positive reaction, 20% (8/39) a low positive reaction, and 18% (7/39) a weak positive reaction. There were only 7 antibody negative horses in the MSU herd. The exposure rate for positive and low positive horses was 64% (25/39).

This rate is similar to previously published reports in the veterinary literature of the seroprevalence of S. neurona in central Pennsylvania. The high exposure rate of the horses at Morehead State University is indicative of the large reservoir of S. neurona that can be found in the opossum population in Eastern Kentucky. By obtaining this baseline antibody data, this group of horses can now be used for vaccine trials in the future, with less confusion associated with antibody titers from immunization versus titers from actual infection or exposure. The information obtained will be beneficial to horse owners in the Eastern Kentucky region, who may wish to be more informed about the actual incidence of EPM in our area.

Dr. Philip E. Prater, 606/783-2326, p.prater@morehead-st.edu
Department of Agricultural Sciences
Morehead State University, Morehead, Kentucky

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