Amebiasis

KEY FEATURES

Essentials of Diagnosis

• Organisms or antigen present in stools or abscess aspirate

• Positive serologic tests with colitis or hepatic abscess, but these may represent prior infections

• Mild to moderate colitis with recurrent diarrhea

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

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

• Use of human excrement as fertilizer also contributes to transmission

• Disease follows penetration of E histolytica into the intestinal wall, resulting in diarrhea, dysentery, and extraintestinal disease (see Amebic Liver Abscess)

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

• About 100,000 people die from invasive E histolytica each 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 bloody stools

• Physical findings with 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

• Amebic liver abscess is most common extraintestinal manifestation (see Amebic Liver Abscess)

DIAGNOSIS

Laboratory Tests

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

• E histolytica and E dispar cannot ...