Microbiology and Pathology
Trypanosoma cruzi causes Chagas disease (American trypanosomiasis) and is transmitted among mammalian hosts by blood-sucking triatomine bugs. Organisms disseminate through the bloodstream, preferentially infecting cardiac, skeletal, and smooth-muscle cells.
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; however, given rapid urbanization and migration, the distribution of cases is extending to cities. An estimated 5.7 million people are infected, including >1 million individuals with chronic cardiomyopathy.
Acute infection resolves spontaneously—without treatment—in 5–10% of pts infected with T. cruzi; otherwise, pts develop chronic infection, with 30–40% sustaining detectable organ damage of variable severity.
- Acute disease develops 1–2 weeks after a bite by the triatomine bug, with >90% of individuals remaining asymptomatic or having a mild febrile illness. Local swelling develops at the inoculation site and is referred to as a chagoma if on the skin or as Romaña’s sign if on the eyelid. Disease resolves spontaneously within 4–8 weeks.
- Chronic disease is indeterminate until there are clinically apparent complications (the determinate form of chronic disease), which generally present as cardiac and/or digestive disorders years to decades after the initial infection. Symptoms include dyspnea, chest pain, palpitations, syncope, sudden death, stroke, dysphagia, regurgitation, constipation, fecaloma, volvulus, and peripheral neuropathy. The 5-year mortality rate is as high as 63% and is typically related to cardiac issues.
- Immunosuppressed pts may develop reactivation of acute disease, which can present as myocarditis, erythema nodosum, panniculitis, Toxoplasma-like focal brain lesion, or meningoencephalitis.
Microscopic or PCR examination of peripheral blood, CSF, or other body fluids may reveal organisms in cases of acute Chagas disease. Chronic Chagas disease is diagnosed by detection of specific IgG antibodies. Given the frequency of false-positive results, diagnosis requires confirmation by at least two serologic assays.
Treatment: Chagas Disease
- Treatment is effective during the acute and early chronic phases (i.e., in pts <18 years of age), but its efficacy in pts >18 years of age is not known.
- Treatment may protect against the development of later cardiac damage, but it is ineffective against digestive complications or preexisting chronic cardiomyopathy.
- Only two drugs—nifurtimox and benznidazole—are available to treat Chagas disease.
- Benznidazole (5 mg/kg qd in two divided doses for 30–60 days) is the recommended first-line drug.
- Nifurtimox (15 mg/kg qd in 3–4 divided oral doses for 60–90 days) reduces symptom duration, parasitemia level, and mortality rate but offers a parasitologic cure in only ∼70% of cases.
- Both drugs have a number of side effects. Benznidazole is better tolerated in adults.
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