Chagas Disease (American Trypanosomiasis)

Definition

• Goldman-Cecil Medicine, Chapter 318

The Pathogen

Epidemiology

• Transmitted by triatomine bugs (reduviid "kissing bugs"), which defecate near their bite wound after taking a blood meal at night. The trypomastigote in insect feces enters through abraded skin or mucous membranes - not through the bite itself.
• Reservoirs: armadillos, wood rats, raccoons, opossums. Dogs are the main domestic reservoir.
• Vectors are found from southern Argentina to the southern United States.

• ~6-8 million people chronically infected in 21 endemic countries (Latin America, not Caribbean islands)
• ~28,000 new cases and ~12,000 deaths annually (PAHO, 2018)
• Vector control programs since 1991 have dramatically reduced transmission; Uruguay (1997), Chile (1999), and Brazil (2006) were certified free of vector transmission.

• Estimated 240,000-350,000 T. cruzi-infected persons in the US, mainly Latin American immigrants
• Autochthonous (locally acquired) acute Chagas disease is extremely rare - only 7 confirmed cases ever reported
• Blood donor screening started in 2007; ~1 in 13,300 donors confirmed positive
• 63-315 babies estimated born with congenital Chagas disease per year in the US

• Blood transfusion and organ transplantation
• Congenital (mother-to-child)
• Oral (contaminated food or juice - documented outbreaks in Brazil)
• Laboratory accidents
• Goldman-Cecil Medicine, Chapter 318; Rosen's Emergency Medicine, Chapter

Lifecycle

1. Triatomine bug ingests blood from an infected mammal, taking up trypomastigotes
2. Trypomastigotes differentiate into epimastigotes in the midgut, then back into metacyclic trypomastigotes in the hindgut
3. Bug defecates near the bite; trypomastigotes in feces enter host through wound, conjunctiva, or mucosa
4. Inside host cells (cardiac myocytes, smooth muscle, macrophages), trypomastigotes convert to amastigotes and replicate by binary fission
5. Amastigotes convert back to trypomastigotes, rupture the cell, and disseminate via bloodstream
6. A feeding bug ingests trypomastigotes from infected blood, completing the cycle

Pathobiology

Histology: T. cruzi amastigotes in cardiac muscle of a child who died of acute Chagas myocarditis (H&E x900) - Goldman-Cecil Medicine

Clinical Phases

1. Acute Phase

• Usually affects children; can occur at any age
• Chagoma: indurated skin lesion at site of parasite entry, with local lymphadenopathy
• Romaña sign (pathognomonic but rarely seen): painless, unilateral periorbital/palpebral edema when conjunctiva is the entry point
• Systemic: fever, malaise, anorexia, facial and lower extremity edema, generalized lymphadenopathy, hepatosplenomegaly
• Severe myocarditis (occasionally fatal) and rare meningoencephalitis can occur
• Resolves spontaneously in 6-8 weeks even without treatment, transitioning to the indeterminate phase

2. Indeterminate (Latent) Phase

• Subpatent parasitemia, no symptoms or signs
• Specific IgG antibodies detectable
• Can persist for the patient's lifetime (~70-80% of infected people remain here forever)

3. Chronic Phase (develops in ~20-30% of infected persons over years to decades)

• ECG changes: RBBB, left anterior fascicular block, PVCs - often the earliest signs
• Arrhythmias: ventricular tachycardia, complete heart block, atrial fibrillation, sudden cardiac death
• Sustained monomorphic VT from scar-related reentry (typically inferolateral LV, RBBB morphology with right axis)
• Biventricular dilated cardiomyopathy; right-sided failure predominates in advanced disease
• Apical LV aneurysm - characteristic feature
• Mural thrombi leading to stroke, pulmonary embolism, or peripheral arterial embolism
• Chronic Chagas disease is an independent risk factor for stroke

• Megaesophagus: dysphagia, regurgitation, aspiration - indistinguishable from idiopathic achalasia manometrically and radiographically; LES dysfunction occurs late
• Megacolon: constipation, obstipation, toxic megacolon risk
• Other: megaduodenum, megaureter

Diagnosis

• Wet mount / Giemsa-stained blood smear: motile trypomastigotes in anticoagulated blood or buffy coat
• PCR: most sensitive method; also used for congenital disease and immunosuppression-driven reactivation
• Culture in special liquid media (slower)

• Serology (standard): requires two different positive tests (ELISA + indirect immunofluorescence, or chemiluminescence) detecting IgG against T. cruzi antigens
• Cross-reactions can occur with malaria, syphilis, leishmaniasis, and some collagen vascular diseases
• PCR sensitivity in chronic disease is 44-100% - useful for borderline serology, suspected congenital/acute disease, or post-treatment monitoring; a negative PCR does not exclude infection

Treatment

Antiparasitic Drugs

• All patients with acute or congenital infection
• All chronically infected children up to age 18
• Reasonable to treat anyone up to age 18 years known to have acquired infection within the past 17 years

• Congenital Chagas in neonates: >90% cure with benznidazole
• Acute phase (nifurtimox): ~70% parasitologic cure; reduces symptoms and mortality
• Adults with long-standing chronic infection: cure rates may be <10%
• The landmark BENEFIT trial (adults with established Chagas cardiomyopathy treated with benznidazole) showed that parasitemia suppression did not translate into reduced cardiac outcomes - this remains the subject of ongoing debate

• Benznidazole: rash, peripheral neuropathy, granulocytopenia
• Nifurtimox: anorexia, nausea/vomiting, weight loss, insomnia, restlessness, paresthesias, polyneuritis, seizures

Symptomatic Management (Chronic Chagas Cardiomyopathy)

• Heart failure: standard therapy (ACE inhibitors, beta-blockers, diuretics, aldosterone antagonists)
• Arrhythmias: antiarrhythmics, ICD placement for sustained VT or high risk of sudden death
• Heart block: permanent pacemaker
• Thromboembolism: anticoagulation
• End-stage: cardiac transplantation (with immunosuppression monitoring for reactivation)

GI Mega-syndromes

• Treatment of megaesophagus/megacolon mirrors that of idiopathic achalasia (pneumatic dilation, surgical myotomy for esophagus; bowel resection for severe megacolon)
• Antiparasitic treatment is of no proven benefit for established chronic GI disease

Special Populations

• T. cruzi reactivation can occur, presenting with severe myocarditis or meningoencephalitis
• A 2024 systematic review (PMID 38697392) found pooled reactivation rates are substantial and that this remains a serious concern in transplant recipients

• Congenital transmission rate ~5% in seropositive mothers
• Most congenitally infected babies are asymptomatic, but some have fever, hepatosplenomegaly, myocarditis
• All babies born to seropositive mothers should be tested

Prevention and Control

• Vector control: insecticide spraying of domiciliary triatomines, housing improvement (replastering walls, replacing thatched roofs)
• Blood donor screening: universal in endemic countries; selective in the US since 2007
• Organ donor screening: recommended for donors from endemic regions
• No vaccine currently available

Key Points Summary