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Chagas' disease
is infection with Trypanosoma cruzi,
transmitted by Triatominae bug bites. Symptoms begin with a skin
lesion or unilateral periorbital edema; progress to fever, malaise,
generalized lymphadenopathy, and hepatosplenomegaly; in some, chronic cardiomyopathy,
megaesophagus, or megacolon occurs. Diagnosis is by detecting
trypanosomes in peripheral blood or aspirates from infected organs.
PCR, serologic tests, and xenodiagnosis may be helpful. Treatment
is with nifurtimox or benznidazole.
Etiology
and Pathophysiology
T. cruzi is transmitted by Triatominae (reduviid, kissing, or assassin) bugs. While biting, infected bugs deposit feces containing metacyclic trypomastigotes on the skin. These infective forms enter through the bite wound or penetrate mucous membranes. The parasites then invade macrophages at the site of entry, transform into amastigotes that multiply by binary fission, and are released as trypomastigotes into the blood and tissue spaces, whence they infect other cells. Cells of the reticuloendothelial system, myocardium, muscles, and nervous system are most commonly involved. Reservoirs include dogs, cats, opossums, rats, and other animals. Infection can also be transmitted by blood transfusion, organ transplantation, or transplacentally.
Infected Triatominae are found in North, Central, and South America. More than 20 million people in the Americas are infected with T.
cruzi, but the prevalence has been decreasing due to control measures. In some rural parts of South America, Chagas' disease has been a leading cause of death. Vector-borne disease is rare in the US, but some Latin American immigrants living in the US are chronically infected. These people are potential sources of transmission by blood transfusion or organ donation.
Symptoms and Signs
Acute infection is followed by a latent (indeterminate) period, which may remain asymptomatic or progress to chronic disease. Immunosuppression may reactivate latent infection, with high parasitemia and a 2nd acute stage, skin lesions, or brain abscesses. Congenital transmission occurs in 1 to 5% of pregnancies and results in abortion, stillbirth, or chronic neonatal disease with high mortality.
Acute infection in endemic areas usually occurs in childhood and can be asymptomatic. When present, symptoms start 1 to 2 wk after exposure. An indurated, erythematous skin lesion (a chagoma) appears at the site of parasite entry. When the inoculation site is the conjunctiva, unilateral periocular and palpebral edema with conjunctivitis and preauricular lymphadenopathy are collectively called Romaña's sign. Acute Chagas' disease is fatal in a small percentage of patients due to acute myocarditis with heart failure or acute meningoencephalitis. In the remainder, symptoms subside without treatment. Primary acute Chagas' disease in immunocompromised patients, such as those with AIDS, may be severe and atypical, with skin lesions and brain abscesses, although the latter are rare.
Chronic disease develops in 20 to 40%, after a latent phase that may last years or decades. Chronic cardiomyopathy leads to flaccid enlargement of all chambers, apical aneurysms, and localized degenerative lesions in the conduction system, producing heart failure, syncope, sudden death due to heart block or ventricular arrhythmia, and thromboembolism. ECG may show right bundle branch or complete heart block. GI disease produces symptoms resembling achalasia or Hirschsprung's disease. Chagas' megaesophagus presents as dysphagia and may lead to pulmonary infections from aspiration or to severe malnutrition. Megacolon may result in prolonged periods of obstipation and intestinal volvulus.
Diagnosis
The number of trypanosomes in peripheral blood is high during the acute phase and readily detected by examination of thin or thick smears. In contrast, few parasites are present in blood during latent infection or chronic disease. Definitive diagnosis may be made by examination of aspirates from organs such as lymph nodes. Serologic tests are sensitive but may yield false-positive results in patients with visceral or mucocutaneous leishmaniasis or other diseases. Other diagnostic approaches include xenodiagnosis (by examining the rectal contents of laboratory-raised bugs after they take a blood meal from a suspected patient) and detecting PCR-amplified parasite DNA in blood or tissue fluids.
Treatment
and Prevention
Treatment in the acute stage rapidly reduces parasitemia, shortens the clinical illness, and reduces risk of mortality but often does not eradicate the infection. Treatment of children and young adults with indeterminate infections has been recommended, but many are not cured. Treatment in the chronic stage is symptomatic. Chronic organ damage, which may be caused in part by host inflammatory responses, appears to be largely irreversible. Supportive measures include drugs for heart failure, pacemakers, antiarrhythmic drugs, cardiac transplantation, esophageal dilation, and GI tract surgery.
The only effective drugs are nifurtimox (2 to 2.5 mg/kg po qid for 3 to 4 mo in adults; 4 to 5 mg/kg qid for 3 mo in 1- to 10-yr-old children; 3 to 3.75 mg/kg qid for 3 mo in 11- to 16-yr-old children) or benznidazole (2.5 to 3.5 mg/kg po bid for 1 to 3 mo for adults; 5.0 mg/kg bid for children ≤ 12 yr). These long treatment courses are often associated with severe GI adverse effects, peripheral neuropathy, poor tolerance, and low compliance.
Plastering walls and replacing thatched roofs or repeated spraying of houses with residual insecticides can control Triatominae bugs. Infection in travelers is rare and can be avoided by not sleeping in such dwellings or by using bed nets if forced to do so.
Transfusion-induced Chagas' disease is a major health problem in endemic areas. A small number of cases have been reported in the US. Although screening for antibodies has been proposed,US blood banks currently rely on historical information to exclude potentially infected donors. Transfusion-induced Chagas' disease can also be prevented by adding gentian violet to blood in endemic areas if blood screening with serologic tests is not possible.
Last full review/revision November 2005
Content last modified November 2005
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