Pathophysiology

Transmission of T cruzi infection occurs when the triatomine bug defecates near the site of the bite wound, depositing the parasite T cruzi where it enters through mucosa located in the eyes, mouth, or skin.6 The parasite then invades macrophages at the initial entry site and enters the bloodstream, resulting in an immunoinflammatory response manifesting primarily in tissues of the heart, gastrointestinal tract, and central nervous system.6


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Clinical Presentation

Chagas disease may have a sudden presentation followed by a brief illness phase. The World Health Organization (WHO) categorizes disease presentation into 2 phases.  The initial acute illness occurs immediately after contact with the organism and lasts a few weeks to several months.  During the acute phase, which involves a high concentration of circulating parasites in the blood stream, symptom presentation may include fever, swelling at the site of infection, lymphadenopathy, fatigue, rash, myalgia, anorexia, eyelid swelling/purplish in color (Romana’s sign), headache, and/or tachycardia.1,7,8 Mortality due to myocarditis or encephalitis/meningitis has been reported in rare cases during the acute phase.9


The “chronic indeterminate” phase is characterized by a prolonged period of time during which the patient is asymptomatic, and there is no evidence of circulating parasitic infection in the blood stream.7

Untreated parasitic infection may progress to the chronic phase, which would not present until 10 to 20 years after initial infection.  The chronic phase is characterized by severe inflammation of the myocardium or brain lining.  According to the US Centers for Disease Control and Prevention (CDC), an estimated 20% to 30% of infected individuals will develop life-threatening and debilitating medical conditions usually complicated with cardiac, digestive, and neurologic sequelae including cardiac arrhythmias, heart failure, sudden cardiac arrest, esophageal enlargement with difficulty swallowing, and dilated colon with difficulty passing stool.1,7-9

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Signs and symptoms of acute and chronic presentations of Chagas disease are listed in Table 1.

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Differential Diagnosis

Depending on the duration of time elapsed from inoculation, severity of the infection, and the tissue and/or organ involvement, the differential diagnosis can range from simple flu or viral presentation to myocardial tissue involvement, which may include myocarditis and myopericarditis.9

Other differential diagnoses to consider are listed in Figure 1.

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Diagnosis

Diagnostic technique used to identify the presence of Chagas disease is dependent on the phase of the infection (eg, acute vs chronic).  In the acute phase, a diagnosis of Chagas disease is made by observation of T cruzi in the bloodstream or cerebrospinal fluid.10 The presence of trypomastigotes can be noted on blood film examination during the acute phase.11 Because parasitemia is low in the chronic phase of Chagas disease, diagnosis requires careful consideration of the patient’s history and symptomatology, as well as confirmation of suspicion by 2 different serologic tests.  Currently, the US Food and Drug Administration has approved 2 enzyme-linked immunosorbent assays (ELISAs) for clinical testing and one ELISA for confirmatory testing.10