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Microbiology and Pathology
Trypanosoma cruzi causes Chagas disease (American trypanosomiasis) and is transmitted among mammalian hosts by hematophagous reduviid bugs. Organisms disseminate through the lymphatics and the bloodstream, often parasitizing muscles particularly heavily.
T. cruzi is found exclusively in the Americas and causes disease mostly among the poor in rural areas of Mexico and Central and South America. An estimated 8 million people are chronically infected, with 14,000 deaths annually.
An indurated area of erythema and swelling (the chagoma) with local lymphadenopathy develops ≥1 week after parasite invasion and generally precedes malaise, fever, anorexia, and edema of the face and lower extremities.
- Romaña’s sign—unilateral painless edema of the palpebrae and periocular tissues—occurs when the conjunctiva is the portal of entry.
- Acute disease resolves spontaneously within 4–8 weeks, and pts enter an asymptomatic phase of chronic infection.
- Symptomatic chronic disease becomes apparent years or even decades after initial infection.
- Cardiac symptoms are common and include rhythm disturbances, segmental or dilated cardiomyopathy, and thromboembolism.
- Pts can develop megaesophagus and suffer from dysphagia, odynophagia, chest pain, and regurgitation.
- Megacolon may develop, leading to abdominal pain, chronic constipation, fecaloma formation, obstruction, and volvulus.
Microscopic examination of fresh anticoagulated blood, the buffy coat, or blood smears may reveal organisms in cases of acute Chagas disease. Serology has no major diagnostic role in acute disease, but PCR assays can be helpful. Chronic Chagas disease is diagnosed by detection of specific IgG antibodies. Given the frequency of false-positive results, a positive result should be confirmed by at least two additional assays.
- Only two drugs—nifurtimox and benznidazole—are available to treat Chagas disease; neither is entirely effective.
- Nifurtimox (8–10 mg/kg qd in four divided oral doses for 90–120 days) reduces symptom duration, parasitemia level, and mortality rate but offers a parasitologic cure in only ~70% of cases.
- Benznidazole (5 mg/kg qd in two or three divided doses for 60 days) is the drug of choice in Latin America and may provide parasitologic cure rates >90%.
- Both drugs have a number of side effects.
- Treatment of chronic Chagas disease is controversial; no adequate studies demonstrate efficacy. However, a panel of experts convened by the CDC recommends that pts <50 years old with presumably long-standing T. cruzi infection be offered treatment.