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American trypanosomiasis, or Chagas disease, is a zoonotic protozoal infection caused by Trypanosoma cruzi. Chagas is spread by triatomine insects with a large variety of mammals serving as natural reservoirs. Disease is limited to the Western hemisphere and is most common in areas of substandard housing as the vector insects proliferate in adobe, unfinished brick walls, and in thatched roofs. Chagas is considered the most important protozoal disease in the Americas, surpassing malaria in morbidity and mortality. It is estimated that 10 million people are infected, including 300,000 immigrants within the United States.
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Chagas is usually acquired during childhood and persists for life. Infection occurs when the insect defecates while taking a blood meal and the infectious stool is rubbed into the bite wound or a mucous membrane (often the conjunctiva). Acutely, infection is often asymptomatic but can present with a skin lesion at the infection site (chagoma), fever, adenopathy, myocarditis, and hepatosplenomegaly. The organism can be isolated during the indeterminate phase (years or even lifespan). Chronically, about 30% develop a cardiomyopathy with progressive biventricular heart failure. Severe arrhythmias, including complete heart block, are common. Approximately 10% of patients will develop digestive complications due to loss of lumen wall neurons, including megaesophagus and megacolon.
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During acute infection, trypanosomes are seen on the blood smear and polymerase chain reaction (PCR) is useful for diagnosis, but serology is typically negative. Serologic assays are used to diagnose chronic disease. Blood culture and xenodiagnosis can also be used but lack sensitivity.
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Management and Disposition
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Patients presenting with acute symptoms are treated with benznidazole or nifurtimox. Patients with chronic disease should be worked up with an electrocardiogram (ECG) and echocardiography and referred as indicated. Antitrypanosomal treatment is warranted in the indeterminate phase of chronic infection and in those with early-stage cardiomyopathies.
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Chagas is the most common cause of cardiomyopathy in many Latin American countries. The disease should also be considered in patients with complete heart block or other arrhythmias.
Chagas is surprisingly common in wild and domestic mammals in the Southern and Southwest United States. The prevalence in Tennessee dogs is 6.4% and is higher in wild animals such as raccoons, skunks, and rodents.
Human infection in the United States is rare since the vector insects are uncommon inside modern housing, but occasional cases have been reported in those without a history of travel.
Universal screening of blood for Chagas is now routine in the United States.
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