Muscular Sarcocystis Infections in Horses in North America: Etiology, Clinical Disease, Personal Perception, and Deposition of Specimens in the Smithsonian Museum

Uncertainty shrouds the number and identity of the species of Sarcocystis infecting horses in the United States. Horses are intermediate hosts for Sarcocystis fayeri, for which the domestic dog is the definitive host. Clinical signs and lesions associated with S. fayeri are not defined. Granulomatous myositis, especially involving the chest and dysphagia, is one of the clinical presentations associated with S. fayeri infections. Whether S. fayeri is the sole species that forms sarcocysts in equine muscles in the United States is not clear. Little is known of the molecular diagnosis of Sarcocystis species in the muscles of horses. One of us (J.P.D.) has studied equine sarcocystosis for the past 5 decades. Here, we review the status of these aspects from a historical and personal perspective.