Amebiasis is intestinal and extraintestinal disease caused by the protozoan parasite Entamoeba histolytica, transmitted by ingestion of cysts from fecally contaminated food, water, or hands. WHO estimates 35-50 million symptomatic cases globally each year and 40,000-100,000 deaths, making it the second deadliest parasitic infection worldwide after malaria.
Amebiasis (ICD-10: A06) is infection of the colon and occasionally other organs by Entamoeba histolytica, a pseudopod-forming protozoan parasite. The lifecycle has two forms. Cysts — the infective, environmentally hardy quadrinucleate stage — are shed in feces and ingested by the next host. Once inside the small intestine, cysts excyst into trophozoites that colonize the colon.
The key symptoms of Amebiasis are: Gradual onset over 1-4 weeks of crampy abdominal pain and loose stools — slower than the abrupt presentation of bacterial dysentery, helping distinguish amebic from shigella or salmonella colitis., Bloody mucoid diarrhea with small-volume stools and tenesmus — the classic amebic dysentery picture, often 6-10 stools per day with visible blood and mucus., Lower abdominal pain and cramping that worsens with defecation, sometimes localized to the right lower quadrant if cecal involvement predominates., Variable or absent fever — many patients with amebic colitis are afebrile, in contrast to the high fevers typical of shigellosis or bacterial enterocolitis., Weight loss and fatigue over weeks of untreated invasive disease, sometimes the dominant symptom in chronic amebic colitis., Right upper quadrant pain, fever, and hepatomegaly in amebic liver abscess — pain is dull, constant, and may radiate to the right shoulder., Cough, pleuritic chest pain, and 'anchovy paste' brown sputum in pleuropulmonary amebiasis from rupture of liver abscess through the diaphragm..
Diagnosing amebiasis requires distinguishing E. histolytica from morphologically identical non-pathogenic Entamoeba species — a task that traditional stool microscopy cannot do reliably. Microscopy that identifies 'Entamoeba histolytica/dispar/moshkovskii' on the basis of cyst morphology is reported in many laboratories worldwide and overestimates true infection rates roughly 10-fold. The 2015 WHO position and the CDC current recommendation is to use either a stool antigen test specific for the E. histolytica galactose/N-acetylgalactosamine lectin or stool PCR to confirm the pathogen. Antigen tests have sensitivity 80-95% and specificity over 90% on fresh unpreserved stool; PCR exceeds 90% sensitivity and remains positive on preserved or refrigerated specimens. For amebic colitis, colonoscopy can reveal flask-shaped ulcers with relatively normal intervening mucosa; biopsy edges show trophozoites with ingested erythrocytes — pathognomonic when seen. For amebic liver abscess, ultrasound is the first-line imaging modality, showing a round or oval hypoechoic lesion typically in the right lobe; CT and MRI further characterize the lesion and exclude pyogenic abscess. Serology (indirect hemagglutination assay or ELISA) is highly sensitive (over 90%) in invasive disease, especially liver abscess, but does not distinguish past from current infection in endemic populations. The combination of compatible imaging plus positive serology plus exclusion of pyogenic abscess by clinical context is usually diagnostic. Differential diagnoses include shigellosis, salmonellosis, campylobacter, inflammatory bowel disease, ischemic colitis, and pseudomembranous colitis for intestinal disease, and pyogenic liver abscess, hydatid cyst, and hepatocellular carcinoma with central necrosis for liver disease.
With timely diagnosis and adequate combined tissue-plus-luminal therapy, the prognosis for amebiasis is excellent. Amebic colitis resolves clinically within 3-7 days of starting metronidazole or tinidazole, with parasitological cure exceeding 90% when paired with a luminal agent. Uncomplicated amebic liver abscess has mortality under 1% with prompt medical treatment; radiographic cavity resolution lags clinical recovery by months but typically completes by 9 months. Mortality rises sharply with complications: fulminant colitis with perforation exceeds 50%, rupture of liver abscess into pericardium can exceed 70%, and pleuropulmonary disease carries 15-30% mortality even with treatment. Risk factors for poor outcome include delayed diagnosis (especially when steroids were given for misdiagnosed IBD), pregnancy, malnutrition, age extremes, large or multiple abscesses, and immunosuppression. Recurrence is uncommon after adequate treatment but reflects ongoing exposure in endemic regions — prevention focuses on water and food safety rather than long-term prophylaxis. Children in highly endemic communities can have repeated infections; cumulative growth and cognitive impacts of recurrent diarrheal disease are well-documented.
Infectious disease or tropical medicine specialist input is recommended for any imaging-confirmed amebic liver abscess, any suspected amebic colitis requiring distinction from inflammatory bowel disease before starting steroids, any failure of first-line therapy, any case in pregnancy or immunosuppression, and any institutional outbreak. Primary care manages straightforward asymptomatic cyst passage well using standard luminal regimens.
Find specialists →Clinical improvement in amebic colitis begins within 24-48 hours of starting nitroimidazole therapy; full symptom resolution within 7-10 days. Amebic liver abscess pain and fever resolve within 3-7 days; radiographic cavity persists for 3-9 months, with progressive shrinkage on serial ultrasound. The luminal-agent course adds 7-10 days. Confirmatory stool testing is recommended 4-6 weeks after treatment completion. Return to normal activities is generally possible within 2 weeks of starting therapy for uncomplicated colitis; 4-6 weeks for liver abscess.
Rest during acute disease and abscess resolution. Light activity may resume once fever and diarrhea have settled, typically within 1-2 weeks. After amebic liver abscess, avoid heavy lifting and contact sport for 4-6 weeks to reduce risk of bleeding into a partially-resolved cavity.
Look for a clinician with access to E. histolytica-specific antigen testing or PCR — many regions still rely on microscopy that overdiagnoses non-pathogenic Entamoeba. For suspected liver abscess, interventional radiology backup is essential. In endemic countries, public hospitals and government infectious disease departments routinely handle large case volumes and tend to have established protocols.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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