Amebiasis

Key Features

Essentials of Diagnosis

• Mild to moderate colitis with recurrent diarrhea

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

• Hepatic abscess: 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 worse 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 typically made by identifying organisms in the stool

• Molecular diagnosis is possible from multi-pathogen panels, which are sensitive and specific, but expensive

• E histolytica and E dispar cannot be distinguished, but identification of amebic ...