Pathophysiology of Chagas disease
1)Â Chagas disease is a s systemic infection caused by protozoan Trypanosoma cruzi 2) occurs in an acute and chronic form (which is usually asymptomatic but can affect heart and cause megacolon and megaesophagus) 3) transmitted via bite of triatomine or reduviid bug, which defecates onto skin after taking a blood meal
Signs and Symptoms
Acute phase – 1) fever 2) malaise 3) anorexia 4) indurated lesion at site of parasite entry (chagoma) 5) hyperplasia of regional lymph nodes 6) positive Romana’s sign – unilateral painless swelling of periocular tissue 7) morbilliform rash 8) facial swelling 9) lower extremity edema 10) hepatosplenomegaly 11) in virtually patients, the acute illness resolves Chronic phase – 12) can appear years to decades later 13) chronic constipation 14) abdominal pain 15) volvulus 16) chest pain 17) dysphagia 18) odynophagia 19) regurgitation 20) aspiration pneumonitis due to achalasia 21) sudden cardiac arrest (especially in young people)22) sudden cardiac rupture
Characteristic Test Findings
EKG – 1) right bundle branch block 2) complete AV block 3) bradyarrhythmias and tachyarrhythmias Laboratory – 4) diagnosis in acute phase is by direct visualization of organism; in chronic phase, by antibody titers
Histology/Gross Pathology
1) apical aneurysms in heart 2) mural thrombi 3) thinned ventricular walls 4) biventricular enlargement 5) lymphocytic infiltrate and interstitial fibrosis in myocardium 6) myocardial cell atrophy 7) pseudocysts in affected tissue 8) decreased number of neurons in myenteric plexus 9) C-shaped organism
Associated Conditions
1) increased mortality in HIV/AIDS 2) increased mortality in transplant patients
Inheritance/Epidemiology
1)Â Chagas disease is most common in extreme southern USA and throughout Central and South America in poor rural areas 2) occurs in USA in immigrant population from these areas – likely 100,000 people iwth Chagas disease at least living in USA are infected 3) not screened for in many blood and organ donors in USA and many cases of transfusion-related infection have occurred
Treatment
1) nifurtimox for 90-120 days with variable results (only drug available in the USA) 2) benznidazole (available in South America)
Tips for USMLE
1) Romana sign is the classic finding in acute Chagas disease and is painless unilateral swelling of periocular tissues when portal is the eye/conjunctiva 2) the two main areas of involvement are the heart and the GI tract 3) most deaths in Chagas disease are the result of cardiac involvement
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