Texas Equine Veterinary Association

• 15 • Table 1: Characteristics of EPM etiologic agents Sarcocystis neurona Neospora hughesi Toxoplasma gondii Life cycle Two-host life cycle Definitive host: opossum Intermediate hosts: skunks, raccoons, armadillos, cats, passerine birds, sea otters and horses (see Figure 2) Poorly characterized. Definitive host: unknown but likely a wild or domestic canid Intermediate hosts: horses Definitive host: cat Intermediate hosts: birds and mammals Role of horse Dead-end and intermediate host. 4 Intermediate host. Intermediate host. Seroprevalence (U.S.) 78% 2 34% 2 6.5% 5 Risk factors Age (generally young performance horses) Stress Co-morbidity Exercise Environment (wooded areas; previous history of EPM on premises) Immune compromised Older horses Pregnant animals Co-morbidity Cats on premises Immune compromised Clinical signs Asymmetrical weakness, ataxia, dysmetria and focal muscle atrophy (May vary depending on part of central nervous system parasitized) Asymmetrical weakness, ataxia, dysmetria and focal muscle atrophy plus signs of co-morbidity Synonymous with S. neurona in documented EPM cases Notes Horse infected by ingesting food/water contaminated with opossum feces Once infected, infected for life. Evidence of transplacental transmission EPM-suspect horses were 3.6 times more likely to have a serum titer of 320 to T. gondii compared to non-neurologic horses 3 (rose to 6.4 times in autumn) Figure 1: While some regions of the country have a higher seroprevalence than others, overall S. neurona and N. hughesi seroprevalence in healthy adult U.S. horses is 78% and 34%, respectively. 2 Continued on next page... don't know exactly how. ere are two studies documenting a possible association between T. gondii and EPM—one of which was done by our team at the University of California, Davis. is study found a higher likelihood of elevated serum titers for T. gondii in suspect EPM cases. ere is more follow up to be done in this area. Take-Home Message Making sense of the "gray" areas around EPM continues to be the subject of much study, but our learnings have taken leaps and bounds since the 1970s, when the disease was originally recognized. Much of that knowledge has centered around the causative organisms and how they behave in the horse, which has proven to be key to proper diagnosis and management.

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