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Considerable advances in the clinical pathological and pathogenic aspects of Chagas disease have been made since the Brazilian physician Carlos Chagas described the disease in 1909. The disease caused by the flagellate protozoon parasite Trypanosoma cruzi is transmitted to humans by a blood sucking triatomine and much less frequently by blood transfusion. It is estimated that 18 million are infected and that about 100 million people from Latin America are at risk of contracting T. cruzi infection. One of the most important contributions to the knowledge of Chagas' disease has been the recognition of the natural history of the disease, which can be divided into three well defined periods: 1. The acute stage; 2. An undetermined or undifferentiated stage and 3. The chronic stage. The primary infection (first stage) occurs mostly unrecognized and clinically apparent acute chagasic myocarditis may appear in less than 5% of the infected individuals, usually children living in endemic areas. The majority of the cases of acute myocarditis are mild and reversible. Autopsied cases of acute chagasic myocarditis are uncommon and correspond to exceptionally severe or fulminant forms showing diffuse myocardial damage with myocytolisis, degenerative changes of myocardial fibers and marked intersticial cellular infiltration. The acute clinical manifestations of the infected individuals include fever, muscular pain, sweating, swollen lymph nodes, hepatospienomegaly. Following this initial stage, all patients enter the undifferentiated or undetermined stage of the chronic period (second stage), which lasts between 10 to 20 years. Of these, 20 to 30% (depending on marked geographical differences) develop symptoms or signs of visceral damage conforming the cohort that enter the third stage. Although megaesophagous and megacolon are not uncommon (mainly in Brazil), the most frequent and important clinical manifestation is a dilated cardiomyopathy. Thus, 70% or more of the infected individuals will never show any clinical manifestation of the disease. The ajmaline test and the endomyocardial biopsy are, probably, the most sensitive methods to unmask latent forms of chagasic myocarditis during the undifferentiated stage. In the most advanced stages of chronic chagasic myocarditis, pathological findings are those of a dilated cardiomyopathy. At autopsy, the apical aneurysm with thrombus in it is a frequent and distinctive finding. The histopathological picture is that of an active and chronic microfocal and disseminated myocarditis. In some cases fibrosis may be confluent, which accounts for the electrocardiographic patterns of myocardial necrosis. The widespread distribution of cardiac lesions also constitute the substrate for atrioventricular and intraventricular conduction disturbances and for atrial and ventricular arrhythmias. The clinical diagnosis of Chagas' heart disease is based on a triad of: positive epidemiology, positive serology and a combination of clinical findings (suggestive electrocardiograhic abnormalities, apical aneurysm, cardiac enlargement). The electrocardiogram in the most advanced forms, usually shows sinus bradycardia, right bundle branch block with or without left anterior hemiblock, primary T wave abnormalities, pathological Q waves and multiform ventricular premature beats. The pathogenesis of the myocardial lesions of acute and also chronic chagasic myocarditis appears to be related in large part to autoimmune mechanisms. The lack of correlation between the location and number of parasitized fibers and the severity, type, and extension of degenerative and inflammatory lesions supports this assumption. Experimental and clinical studies have demonstrated the presence of antibodies directed against different components of T. cruzi and crossreacting with human antigens in patients with chronic chagasic myocarditis. Microvascular dysfunction, myocardial ischemia and autonomic nervous system impairment have also been implica |
