• Overview: amebiasis
  • Causative agent of amebiasis call-in protozoan parasite Entamoeba histolytica
    • Two distinct (morphologically identical species) in the Entamoeba complex
      1. E. dispar-resides in the colon; as a stable commensal
      2. E. histolytica (10% of the complex)-shows virulence (varying degrees)
         • severe intestinal infection (dysentery)
         • mild/moderate symptomatic intestinal infection
         • asymptomatic intestinal infection
         • ameboma
         • liver abscess or other type of extraintestinal infection
  • Diagnostic Criteria:
    • Suggestive:
      • Primary: Travelers/immigrants (from E histolytica-endemic regions)-presenting with intestinal symptoms which a range from mild complaints to acute fulminant colitis.
    • Definitive:
      • Cysts or trophozoites in stool or rectal biopsy or trophozoites in other organs, e.g. the liver
      • 95% sensitivity of serology in patients with extraintestinal amebiasis
        • Serology assay much less sensitive in patient with intestinal amebiasis
        • Serologic response: may remain positive for years

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  • Clinical Manifestations-Subjective
    • Intestinal Amebiasis:
      •  90% of infected individuals: asymptomatic (most do not develop illness; infection clears within weeks or months spontaneously)
      •  Symptomatic patient-noninvasive disease {only cysts}:
        •  abdominal pain
        •  increased bowel movement frequency
        •  increasing bowel movement frequency may be intermittent and may alternate with constipation
      •  Symptomatic patients-invasive disease {only trophozoites seen}
        •  symptoms gradual, nonspecific
        •  abdominal pain
        •  watery diarrhea
        •  blood + mucus in stool {amebic dysentery}
        •  Other symptoms relatively mild (appetite often retained) -- generally in contrast to invasive bacterial diarrheas.
        •  With colitis present-segmental ulceration may occur:
          •  Coalescing of segmental ulcers can become superinfected (bacterial) and may lead to toxic megacolon (unlikely)
          •   Ulcerations may perforate, causing peritonitis-alternatively ulcerations may become fibrotic ultimately forming an ameboma.
    • Extraintestinal Amebiasis (Amebic Liver Abscess)
      •  Occurs as a result of previous intestinal infection & may occur concurrently with colitis (frequency: 15%)
      •  Typically:
        • no history of intestinal amebiasis
        • stool examination -- negative
      •  Symptoms/characteristics of liver abscess
        •  acute onset
        •  abdominal dull pain localized to right upper quadrant, epigastrum
        •  dull right shoulder pain-
          • if abscess is in the left liver lobe-pain can radiate to the left shoulder
        •  Patients are likely (frequency: 90%) to have fever, malaise and become anorexic

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  • Clinical Manifestations: Objective
    • Intestinal Amebiasis
      • Physical Exam:
        • Relatively non-ill patient-nonspecific findings
          •  possible lower quadrant pain to palpation
          •  some hepatic tenderness
          • hepatomegaly (abscess not required)
        • More seriously ill patient:
          •  "toxic" appearance with dehydration
          •  abdominal pain (diffuse)
          •  possible palpable mass (ameboma)
          •  possible colonic distention {toxic megacolon}
      • Laboratory: may be normal; most patients-heme-positive stool
    • Extraintestinal Amebiasis (amebic liver abscess)
      • Physical Exam:
        • Most Important Sign: Liver enlargement + pain on palpation (point tenderness, a frequent finding)
        • If abscess located high under diaphragm:
          •  intercostal tenderness
          •  dullness to percussion over right lower chest
          •  decreased breath sounds
      • Laboratory:
        •  > 50% anemia, leukocytosis {left shift}
        •  high fevers: common
        • jaundice: rare
        • eosinophilia: absent
        • often minimal abnormalities in liver tests

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    • Differential Diagnosis
    • Summary of Clinical Features:
      • "A wide spectrum, from asymptomatic carriers ("luminal amebiasis"), to invasive intestinal amebiasis (dysentery, colitis, appendicitis, toxic megacolon, amebomas), to invasive extraintestinal amebiasis (liver abcess, peritonitis, pleuropulmonary abcess, cutaneous and genital amebic lesions)."-CDC http://www.dpd.cdc.gov/DPDx/HTML/Amebiasis.htm

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    • Life-cycle/Laboratory/Microscopy
      • Life Cycle Entamoeba histolytica
      • Laboratory Diagnosis
      • Microscopy 1: Trophozoites of Entamoeba histolytica/dispar
      • Microscopy 2: Trophozoites of Entamoeba histolytica/dispar with ingested erythrocytes
      • Microscopy3: Cysts of Entamoeba histolytica/dispar

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