PATHOGENESIS OF MYOCARDITIS IN ROCKY-MOUNTAIN SPOTTED-FEVER

Abstract

Because [human] myocarditis was frequently present at necropsy in fatal Rocky Mountain spotted fever (RMSF) and ECG alterations may accompany the disease, the pathogenesis of myocarditis in RMSF was studied. Increased heart wt in 8 of 9 cases and increased interstitial volume in 6 of 9 cases suggest that myocardial edema is present. Specific immunofluorescent demonstration of Rickettsia ricketsii in myocardial capillaries, venules and arterioles in 8 of 9 cases correlates well with the patchy distribution of interstitial mononuclear myocarditis and provides the pathogenic mechanism for vascular injury-induced myocardial edema. Absence of left ventricular dilation suggests that severe myocardial failure was not the apparent cause of hypotension, shock and death in RMSF.