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For further information, see CMDT Part 35-07: Amebiasis

Key Features

Essentials of Diagnosis

  • Fever, abdominal pain

  • Amoebae or antigen in stool or abscess aspirate

  • Positive serologic tests but may represent prior infections

  • Hepatomegaly, hepatic abscess on imaging studies

General Considerations

  • The Entamoeba complex contains three morphologically identical species

    • E dispar, which is avirulent

    • E moshkovskii, which is also avirulent

    • E histolytica, which may be an avirulent intestinal commensal or lead to serious disease

  • Humans are the only established host for E histolytica

  • Transmission occurs through ingestion of cysts from fecally contaminated food or water

  • Infection can be transmitted person-to-person

  • Flies and other arthropods also serve as mechanical vectors

  • Disease follows penetration of the intestinal wall, resulting in

    • Diarrhea

    • Dysentery

    • Extraintestinal disease, most commonly liver abscess


  • E histolytica infections are present worldwide but are most prevalent in subtropical and tropical areas under conditions of crowding, poor sanitation, and poor nutrition

  • Of 500 million persons worldwide infected with Entamoeba, most are infected with E dispar and an estimated 10% (50 million) are infected with E histolytica

  • Mortality from invasive E histolytica is about 100,000 per year

  • Severe disease is more common in

    • Young children

    • Pregnant women

    • Persons who are malnourished

    • Persons receiving corticosteroids

  • Hepatic abscesses more common in men

Clinical Findings

Symptoms and Signs

  • Many patients do not have current or a past history of intestinal symptoms

  • Acute or gradual onset of abdominal pain

  • Fever

  • Enlarged and tender liver

  • Anorexia

  • Weight loss

  • Intercostal tenderness

  • Diarrhea is present in a small number of patients

  • Abscesses are most commonly single and in the right lobe of the liver

  • Amebic infections may rarely occur throughout the body, including the lungs, brain, and genitourinary system


Laboratory Tests

  • Leukocytosis and elevated liver biochemical tests

  • Serologic tests for anti-amebic antibodies are almost always positive, except very early in the infection

  • Thus, a negative test in a suspicious case should be repeated in about a week

  • The stool E histolytica antigen test is positive in ~40% of cases; the TechLab II test can also be used to test serum, with good sensitivity if used before the initiation of therapy

  • Examination of stools for the organisms or antigen is frequently negative

Imaging Studies

  • Ultrasonography, CT, or MRI show abscesses as round or oval low-density nonhomogeneous lesions with abrupt transition from normal liver to the lesion and hypoechoic centers

Diagnostic Procedures

  • Percutaneous aspiration

    • May be needed to distinguish between amebic and pyogenic abscesses

    • Best done by an image-guided needle

    • Typically yields brown or yellow fluid

    • Detection of organisms in the aspirate ...

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