Entamoeba histolytica infection (amebiasis)
Entamoeba histolytica is a fecal-orally transmitted protozoan that ranges from asymptomatic cyst passage to invasive amebic colitis with bloody diarrhea to amebic liver abscess, a single right-lobe collection reached by portal spread. Diagnosis requires a stool antigen or molecular test to distinguish it from the nonpathogenic look-alike Entamoeba dispar, and treatment always pairs a tissue amebicide with a luminal agent to eradicate residual cysts.
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What this article covers
- Overview
Definition: amebiasis is infection with the protozoan parasite Entamoeba histolytica, acquired by ingesting infective cysts, that ranges from asymptomatic cyst passage to invasive amebic colitis to…
- Epidemiology
Developing-region and travel exposure: most United States cases are diagnosed in travelers returning from unsanitary tropical or developing regions and in immigrants from areas where amebiasis is endemic.
- Risk factors
Travel to or residence in endemic areas: unsanitary tropical and developing regions with contaminated water or food are the dominant exposure.
- Pathophysiology
Fecal-oral ingestion of cysts: the mature, environmentally resistant cyst is the infective form and survives passage through gastric acid.
- Clinical features
Amebic colitis, the more common presentation: subacute (days to weeks) bloody or mucoid diarrhea with lower abdominal cramping and tenesmus, in contrast to the acute, fulminant onset of bacterial dysentery.
- Differential diagnosis
Shigella dysentery: acute-onset high fever and bloody diarrhea over hours, more fulminant than the subacute course of amebic colitis, with stool culture positive for Shigella.
- Diagnosis
Establish the diagnosis with species-specific stool testing, because microscopy alone cannot confirm it: stool microscopy can visualize Entamoeba cysts or trophozoites but cannot morphologically distinguish pathogenic E.
- Management
Treat every documented E. histolytica infection, including asymptomatic cyst passage, because carriers remain a source of invasive disease and further transmission.
- Complications
Fulminant amebic colitis with perforation or toxic megacolon: the most life-threatening intestinal complication, more likely after inappropriate corticosteroid exposure or in immunodeficient patients.
- Prognosis
Excellent with appropriate two-drug therapy: most patients with uncomplicated amebic colitis or a small-to-moderate liver abscess recover fully with a tissue amebicide followed by a luminal agent.
- Prevention
Safe water and food practices while traveling to or living in endemic regions: drink only bottled or boiled water (boil at least 1 minute, 3 minutes above 6,500 ft altitude), avoid ice of uncertain…
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