Chagas Disease

Chagas disease, also known as American trypanomyiasis, is the most important parasitic disease of Latin America, affecting 10 to 20 million people or more. Of these, 1 million will die prematurely as a result of the disease. Chagas disease affects mostly impoverished people from Mexico to southern South America. Recent population movements and the chronic asymptomatic nature of the disease mean that there are hundreds of thousands of infected individuals in nonendemic countries. Due to its transmissibility by transfusion, transplantation, and transplacentally, Chagas disease can be spread in nonendemic countries where there is no screening of the blood and organ supply for the disease.

Chagas disease is caused by the flagellated protozoan parasite Trypanosoma cruzi. It is transmitted by multiple species of blood-sucking triatomine insects (also known as kissing bugs or reduvid bugs) that interact with humans when they infest thatched homes in poor rural and periurban communities. Chagas disease is a zoonisis (a disease that normally affects animals but may also affect humans) with a variety of animal reservoirs including armadillos, opposums, and domestic animals.

When an infected triatomine bug consumes a blood meal from a human, T. cruzi parasites are excreted in the feces. If the feces come in contact with mucous membranes or penetrates skin, then the resulting local infection may cause a chagoma or a pathognomonic unilateral conjunctivitis known as Romana's sign. A very small number of individuals suffer from fulminant myocarditis or meningoencephalitis; more commonly, acute infection is asymptomatic and unrecognized.

The chronic form of Chagas disease surfaces in about one-third of infected individuals between 10 to 40 years after initial infection. Reactivation of T. cruzi can occur much earlier in the setting of human immunodeficiency virus (HIV) coinfection or in transplant patients.

During the long latent phase, T. cruzi parasites infect and multiply within cardiac and smooth muscle cells. As such, chronic infection affects primarily the cardiac and gastrointestinal systems. Cardiovascular effects include cardiomegally, cardiac aneurysms, and conduction abnormalities from benign electrocardiogram (ECG) changes to serious arrhythmias. These conditions often lead to progressive heart failure or to sudden cardiac death. Gastrointestinal manifestations are due to inflammation and destruction of the autonomic ganglia in the gastrointestinal tissues leading to megacolon and megaesophagus in the most severe cases.

T. cruzi is increasingly being recognized as a heterogenous complex of organisms with variable [Page 372]phenotypic, genotypic, and clinical features. For example, gastrointestinal manifestations of chronic Chagas disease are much more common north of the equator because of the type of T. cruzi strains found in those areas.

Diagnosis of Chagas disease in the acute phase is accomplished by identifying parasites in peripheral blood. During the chronic phase, there are few parasites in the blood and even blood or aspirate cultures are often negative. Other strategies include xenodiagnosis (examining feces of triatomine bugs that are allowed to have a blood meal on the suspect patient) and serologic tests, which are available but have relatively high false-positive rates. Detection of parasite DNA by polymerase chain reaction (PCR) amplification is the most sensitive, specific, and expensive means of diagnosis.

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