Entamoeba histolytica

Aka: Entamoeba histolytica, E. histolytica, Amebiasis, Amebic Dysentery, Ameboma

1. See Also
   1. Diarrhea
   2. Infectious Diarrhea
2. Epidemiology
   1. Prevalence: 10% worldwide
   2. Asymptomatic cyst carriage in 90% cases
   3. Symptomatic cases per year: 50 million worldwide
   4. Fatalities per year: 100,000
3. Risk factors
   1. Mental health institutions (High Prevalence)
   2. Crowded living conditions
   3. Poor sanitation
   4. Travel to endemic areas
      1. Asia
      2. Africa
      3. Latin America
4. Pathophysiology
   1. Two forms
      1. Cyst (12 um diameter): Spheres with up to 4 nucleii
         1. Divides into trophozoites in Small Intestine
         2. Cysts can survive weeks in moist environment
      2. Trophozoite (25 um long)
         1. Contains 1 nucleus and ingested RBCs
         2. Moves via finger-like pseudopods toward colon
         3. Some trophozoites transform into cysts
   2. Results in enterocolitis
      1. Intraluminal disease
         1. Profuse Diarrhea with malabsorption
         2. Ulceration of colon and terminal ilium
         3. Intestinal bleeding
      2. Systemic dissemination
         1. Liver Abscess
         2. Lung Abscess
         3. Brain abscess
   3. Transmission via fecal-oral route
      1. See Waterborne Illness
      2. See Foodborne Illness
      3. Food preparation contaminated by poor hygiene
      4. Human waste used for crop fertilization
      5. Oral-anal sex
5. Symptoms
   1. Acute
      1. Fulminant onset
      2. Cramping, moderate to severe Abdominal Pain
      3. Bloody, profuse Diarrhea
      4. Mucus in stools
      5. Tenesmus
      6. Malaise
   2. Chronic
      1. Normal stools alternate with symptomatic phase
6. Signs
   1. Acute
      1. Fever
      2. Diffuse abdominal tenderness
      3. Dehydration
      4. Weight loss
   2. Chronic
      1. Fever
      2. Tenderness and cramping of cecum and ascending colon
   3. Liver Abscess (within 5 months of onset)
      1. Fever (10-15 of cases)
      2. RUQ Abdominal Pain or liver tenderness
      3. Liver friction rub if Liver Abscess present
      4. Diarrhea (33% of cases)
7. Differential Diagnosis
   1. See Waterborne Illness
   2. See Foodborne Illness
   3. Appendicitis
   4. Inflammatory Bowel Disease (especially Crohn's Disease)
8. Complications
   1. Ameboma growth into intestinal lumen
      1. Risk of Bowel Obstruction
      2. Risk of Intussusception
   2. Toxic Megacolon
   3. Pneumatosis coli
   4. Abscess formation
      1. Lung Abscess
      2. Brain abscess
      3. Liver Abscess
         1. See signs above
         2. Risk of rupture
         3. Risk factors for complication
            1. Multiple cysts or cysts >10 cm in size
            2. Superior right liver lobe involvement
            3. Left liver lobe involvement
         4. Course
            1. Spontaneous resolution by 6 months in 66%
            2. Persist >1 year in 10%
9. Labs
   1. Entamoeba histolytica stool antigen testing (preferred)
      1. Test Sensitivity: 87%
      2. Test Specificity: >90%
   2. Ova and Parasite exam (3 samples required)
      1. Fresh Stool Exam with Microscopy and gross exam
      2. Motile or encysted organisms
      3. Watery stool with mucus or blood
   3. Other tests
      1. Fecal Leukocytes positive
      2. Occult blood positive
      3. Fecal Eosinophilia (Charcot-Leyden crystals present)
10. Diagnostic Testing
    1. Endoscopy
       1. Mimics Crohn's Disease
       2. Colonic Ulcerations
          1. Discrete ulcers of variable depth in right colon
          2. Exudative hyperemic ulcers with small Hemorrhages
    2. Biopsy
       1. Intramural trophozoites at edge of Ulceration
11. Radiology
    1. Barium Enema may show Ameboma
       1. Irregular barium distribution in ascending colon
    2. Right Upper Quadrant Ultrasound
       1. Hepatic Abscess (oval hypoechoic cyst)
12. Management: Acute
    1. Requires combined use of both tissue and luminal agent
    2. Luminal agents for cysts (choose one)
       1. Iodoquinol (Yodoxin) 650 mg PO tid for 20 days
       2. Diloxanide furoate (Furamide) 500 mg PO tid x10 days
       3. Paromomycin 500 mg PO tid for 7 days
    3. Tissue agents for trophozoites
       1. Metronidazole (Flagyl) 750 mg PO tid for 10 days
13. Management: Liver Abscess
    1. Option 1 (preferred)
       1. Metronidazole (Flagyl) 750 mg PO tid for 5 days, then
       2. Paromomycin 500 mg PO tid for 7 days
    2. Option 2
       1. Chloroquine 600 mg PO qd for 2 days, then
       2. Chloroquine 200 mg PO qd for 2-3 weeks
14. References
    1. Kucik (2004) Am Fam Physician 69(5):1161-8
    2. Petri (1999) Clin Infect Dis 29:1117-25