Sarcocystis-associated myocarditis in a domestic cat.

This report describes a 2-year-old spayed female domestic shorthair cat presented because of severe, acute respiratory distress and ultimately diagnosed with myocarditis and secondary congestive heart failure associated with Sarcocystis spp. Despite therapy with oxygen, furosemide, and butorphanol, the cat deteriorated rapidly, became moribund, and was euthanized. Lymphohistiocytic myocarditis associated with protozoal organisms with evidence of secondary congestive heart failure was diagnosed based on gross and histological findings. Protozoal cysts were identified within the myocardium and Sarcocystis-containing cysts were also seen in lingual and periocular striated muscles with associated myositis. Immunohistochemical analysis confirmed that the protozoal organisms were Sarcocystis spp. Molecular identification using polymerase chain reaction identified the etiologic agent as S. arctica/caninum. Although Sarcocystis infection has been documented in striated muscles of cats worldwide, this is typically an incidental finding. If disease occurs, it usually leads to neurologic signs from a Sarcocystis-induced encephalomyelitis. To the best of our knowledge, this is the first report of Sarcocystis spp. affecting the cardiac muscle of a domestic cat with a fatal outcome. Key clinical message: Sarcocystis spp. is a novel cause of heart failure in cats due to lymphohistiocytic myocarditis.