Chagas disease, also known as American trypanosomiasis, is a tropical parasitic illness caused by the protozoan Trypanosoma cruzi . It is endemic to Central and South America and is primarily transmitted to humans by triatomine bugs (also known as “kissing bugs”).
Epidemiology
- Affects approximately 6–7 million people globally .
- Most prevalent in rural and poor housing areas in Latin America.
- Increasingly seen in non-endemic regions (e.g., the U.S., Europe) due to migration.
Life Cycle and Pathogenesis
Vector: Triatomine bugs (Reduviidae family) transmit the parasite through contaminated feces , not the bite itself.
Life Cycle Steps:
- Triatomine bug feeds on human blood, defecating near the bite site.
- Metacyclic trypomastigotes in the feces are introduced via:
- Scratching the bite site,
- Contact with mucous membranes (e.g., conjunctiva),
- Transplacental transmission,
- Blood transfusion or organ transplantation,
- Ingestion of contaminated food or drinks.
- In the host:
- Parasites invade various cell types , especially cardiac and smooth muscle .
- Multiply intracellularly as amastigotes , forming pseudocysts .
- Cells rupture, releasing trypomastigotes into the bloodstream → infect more cells.
Pathogenesis:
- Acute damage from cell lysis and inflammation .
- Chronic damage due to:
- Persistent low-level infection,
- Autoimmune responses ,
- Neuronal destruction , especially of the enteric nervous system and myocardium .
Modes of Transmission
- Vector-borne : Feces of triatomine bug (most common).
- Vertical transmission : Congenital (transplacental).
- Blood transfusion or organ transplant .
- Oral transmission : Ingestion of food or drink contaminated with infected bug feces.
- Laboratory accidents .
Clinical Manifestations
1. Acute Phase (first 4–8 weeks)
- Often asymptomatic (in ~70% of cases).
- Symptoms (when present):
- Fever , malaise, lymphadenopathy,
- Hepatosplenomegaly ,
- Chagoma : Inflammatory nodule at inoculation site,
- Romaña's sign : Unilateral periorbital edema if entry is via conjunctiva,
- Myocarditis and meningoencephalitis (in severe pediatric cases).
💡 Note : Parasitemia is highest during this stage, aiding in diagnosis.
2. Indeterminate Phase
- Lasts for years or decades .
- Patients are asymptomatic , but parasites persist in tissues.
- 60–70% remain in this phase for life.
3. Chronic Chagas Disease (10–30% of cases)
Develops 10–20 years after initial infection.
Cardiac Manifestations (most common)
- Dilated cardiomyopathy ,
- Arrhythmias (especially right bundle branch block),
- Apical aneurysms ,
- Heart failure ,
- Thromboembolism , sudden cardiac death.
Gastrointestinal Manifestations
- Megaesophagus → Dysphagia, aspiration.
- Megacolon → Severe constipation, abdominal distension.
- Due to destruction of enteric plexus neurons .
Reactivation (in immunosuppressed individuals)
- Seen in HIV/AIDS , transplant recipients.
- Presents as meningoencephalitis or myocarditis .
Diagnosis
Acute Phase
- Microscopy : Trypomastigotes seen on peripheral blood smear .
- PCR : High sensitivity for parasite DNA.
- Culture or xenodiagnosis in specialized labs.
Chronic Phase
- Serology (IgG) : ELISA and indirect immunofluorescence assay (IFA).
🧠 At least two serological tests with different principles are recommended.
- PCR may assist but has lower sensitivity in this phase.
Treatment
Antiparasitic Therapy
Most effective in the acute and congenital phases.
| Drug | Mechanism | Notes |
|---|---|---|
| Benznidazole | Produces reactive radicals to damage parasite DNA | First-line; better tolerated |
| Nifurtimox | Generates oxidative stress | More side effects (GI, neurological) |
- Duration : 60–90 days.
- Cure rate : ~60–80% in acute infections.
- Limited efficacy in chronic phase , but may reduce disease progression in early chronic stage.
❌ Contraindications : Pregnancy, severe hepatic/renal failure.
Supportive Management
- Heart failure or arrhythmia : Managed per cardiology guidelines.
- Pacemakers/ICDs : For advanced conduction defects.
- Surgical interventions : For GI megasyndromes if symptomatic.
Prevention and Control
Vector Control
- Insecticide spraying (pyrethroids) in endemic areas.
- Improved housing (cement walls, sealed roofs).
Blood and Organ Screening
- Routine screening of donors in endemic and non-endemic regions with migrant populations.
Congenital Transmission
- Screen pregnant women from endemic areas.
- Treat infected neonates promptly.
High-Yield Notes (USMLE/NCLEX Style)
- 🦠 Trypanosoma cruzi is transmitted by fecal contamination , not the bug bite.
- ❤️ Chronic phase often leads to biventricular heart failure , apical aneurysm , and sudden death .
- 🧠 Romaña’s sign is a key indicator of acute Chagas if entry is via the eye.
- 💊 Benznidazole is first-line for acute and early chronic disease.
- 🏡 Prevention focuses on vector control and housing improvement .
- ⚠️ Always screen blood donors and pregnant women in endemic populations.
