Cardio-histopathological observations on aborted equine fetuses infected with equid herpesvirus 1 (EHV-1)

Twenty-five aborted equine fetuses infected with equid herpesvirus 1 (EHV-1) were examined cardio-histopathologically. The main changes in the heart consisted of interstitial myocarditis and intramyocardial vascular lesions accompanied by degeneration and necrosis of the cardiac myocytes. Vascular pathology of intramyocardial small arteries and arterioles was characterized by endothelial cell necrosis and fibrinoid changes in the media. Eosinophilic intranuclear inclusion bodies characteristic of herpesvirus infection were detected in the myocardial cells and macrophages within and around the inflammatory lesions and in the endothelial cells and medial smooth muscle cells of the damaged vessels. This observation, taken in conjunction with the fact that EHV-1 antigens were detected immunohistochemically in some myocardial and endothelial cells, provides morphological evidence in support of the viral aetiology of the cardiac lesions.