CHAGAS' DISEASE



I. Microbiology and epidemiology
  1. Caused by a flagellated protozoan, Trypanosoma cruzi
  2. The "triatomine" ("kissing") bug takes a blood meal from a human, then defecates trypomastigotes onto the human's skin that invade cells near the bite.  In a complex lifecycle, eventually they are released into the human's bloodstream and invade the tissues
  3. Can also be transmitted in contaminated blood products or organs and through vertical transmission
  4. Endemic from southern U.S. to Argentina, primarily in rural areas
II. Clinical Features
  1. Acute phase
    1. Can last weeks to months
    2. Fever & swelling at site of inoculation ("chagoma")
    3. Rarely can get "Romana's sign" (unilateral palpebral and periocular swelling due to conjunctival exposure to the triatomine bug's feces)
    4. May be subclinical
  2. Chronic phase-Occurs in most patients who aren't treated during the acute phase
    1. 75% remain asymptomatic and have mortality rate similar to general population
    2. 25% develop clinical chronic disease but make not occur until years after infection
    3. Chagasic cardiomyopathy-Most common chronic manifestation
      1. Conduction abnormalities, most often right bundle branch block and left anterior fascicular block, but can get complete heart block
      2. Dilated cardiomyopathy and heart failure
      3. Tachyarrhythmias
      4. Left ventricular aneurysm
    4. Gastrointestinal involvement
      1. Achalasia
      2. Dysphagia
      3. Esophageal reflux
      4. Mega-esophagus and mega-colon with severe constipation and abdominal pain
  3. Congenital disease can occur (may be asymptomatic or manifest with nonspecific signs e.g. low birth weight or prematurity; sometimes have cardiac manifestations)
III. Diagnosis
  1. Peripheral blood smear may show circulating trypomastigotes but usually only in acute disease (requires special preparations, e.g. Giemsa stain)
  2. Antibody testing-Sensitivity and specificty may be suboptimal
IV. Management
  1. Patient should be instructed not to donate blood
  2. 12-lead ECG to screen for heart disease; If abnormalities are found, consider echocardiogram, Holter, and exercise stress testing
  3. If GI symptoms are present consider Barium contrast studies and/or upper & lower endoscopy
  4. Medication
    1. In patients > 50yo with chronic disease, risks of treatment may outweight benefits
    2. As of 2012 the medications for Chagas' disease are available only from CDC under investigational protocols
    3. Evidence of benefit is limited to patients with acute disease
    4. Contraindicated in severe hepatic or renal impairment
    5. Benznidazole x 60d (can cause cutaneous reactions, neuropathy, anorexia, and insomnia)
    6. Nifurtimox x 90d (can cause neuropathy, anorexia, nausea, vomiting, headache, and dizziness)
(Sources include Core Content Review of Family Medicine, 2012)