Spontaneous cardiomyopathy: histopathologic and ultrastructural alterations of turkey heart tissue.

Twelve turkeys poults, 4 to 5 weeks of age, were selected from a farm chosen for the study of spontaneous cardiomyopathy (SC) because of repeated outbreaks in successive flocks. An augmented myocardial mass accompanied the characteristic gross features of cardiomegaly and biventricular dilatation in SC-affected birds. Histologic alterations in myocardium were attributed to artifacts, resulting from unopposed cardiac muscle contraction prior to formalin fixation; specific pathologic lesions were not detected. Ultrastructural artifacts were minimized by perfusion fixation. Salient ultrastructural changes were mild when compared with the changes in the myocardium of nonaffected poults and consisted mainly of Z-band abnormalities. Virus-like particles were identified within sarcoplasmic reticulum of 2 SC-affected birds. The pathogenesis of SC, including acquired and inherited etiologic factors, is discussed.