Sarcocystis fayeri–Induced Granulomatous and Eosinophilic Myositis in Two Related Horses

A new article from Veterinary Pathology is available from entitled “Sarcocystis fayeri–Induced Granulomatous and Eosinophilic Myositis in 2 Related Horses.”Researchers from Oklahoma State University and the University of Tennessee noted that, “Sarcocystosis should be considered a rare cause of granulomatous eosinophilic myositis and choke in horses.”

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This report describes 2 genetically related paint mares, case Nos. 1 and 2, presented to the Oklahoma State University Boren Veterinary Medical Teaching Hospital for chronic weight loss and abnormal gait, respectively. Notable findings in both cases included marked persistent eosinophilia and multiple intramuscular lateral thoracic masses. Histologic examination of masses revealed eosinophilic, centrally necrotic granulomas and marked eosinophilic myositis. Granulomas in case No. 1 also contained intralesional Sarcocystis sp material, and adjacent muscle fibers contained intact protozoal cysts. Case No. 1 developed severe refractory muscle pain and recurrent esophageal dysphagia. At necropsy, disseminated, grossly visible granulomas were present throughout all examined striated muscles. Nested polymerase chain reaction of the 18S rRNA gene revealed >99% homology with Sarcocystis fayeri. Sarcocystis spp are apicomplexan protozoa that infect striated muscle of many omnivorous species, typically without inciting clinical disease. Sarcocystosis should be considered a rare cause of granulomatous eosinophilic myositis and choke in horses.


H.R. Herd, L.A. Starkey, R.J. Panciera, E.M. Johnson, and T.A. Snider, Department of Veterinary Pathobiology, Oklahoma State University; M.M. Sula, Department of Biomedical and Diagnostic Sciences, Collage of Veterinary Medicine, University of Tennessee; and T.C. Holbrook, Department of Veterinary Clinical Sciences, Oklahoma State University.

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