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Key Features

Essentials of Diagnosis

  • Mild to moderate colitis with recurrent diarrhea

  • Severe colitis including bloody diarrhea, fever, and abdominal pain, with potential progression to hemorrhage or perforation

  • Hepatic abscess with fever, hepatomegaly, and abdominal pain

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, and extraintestinal disease (see Amebic Liver Disease)

Demographics

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

  • Urban outbreaks have occurred because of common-source water contamination

  • 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

Clinical Findings

Symptoms and Signs

  • In most infected persons, the organism lives as a commensal, and the carrier is without symptoms

Mild disease

  • Diarrhea may begin within a week of infection, although an incubation period of 2–4 weeks is more common

  • Onset of abdominal pain and diarrhea is gradual

  • Fever is uncommon

  • Periods of remission and recurrence may last days to weeks or longer

  • Abdominal examination may show

    • Distention

    • Tenderness

    • Hyperperistalsis

    • Hepatomegaly

Severe disease

  • Includes colitis and dysentery, with more extensive diarrhea (10–20 stools per day) and the appearance of bloody stools

  • Physical findings of dysentery

    • High fevers

    • Prostration

    • Vomiting

    • Abdominal pain and tenderness

    • Hepatic enlargement

    • Hypotension

  • Fulminant amebic colitis can progress to

    • Necrotizing colitis

    • Intestinal perforation

    • Mucosal sloughing

    • Severe hemorrhage

  • Localized granulomatous lesions (amebomas)

    • Can present after either dysentery or chronic intestinal infection

    • Clinical findings include pain, obstructive symptoms, and hemorrhage and may suggest intestinal carcinoma

Differential Diagnosis

  • Inflammatory bowel disease

  • Giardiasis, Shigella, Salmonella, Campylobacter

  • Irritable bowel syndrome

  • Lactase deficiency

  • Cryptosporidiosis, cyclosporiasis

  • Annular colonic carcinoma, tuberculosis, or lymphogranuloma venereum

Diagnosis

Laboratory Tests

  • Diagnosis is most commonly made by identifying organisms in the stool

  • E histolytica and E dispar cannot be distinguished, but identification of amebic trophozoites or cysts in a symptomatic patient is highly suggestive of amebiasis

  • Stool evaluation for organisms

    • Not highly sensitive (~30–50% ...

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