Amoebiasis is infection by Entamoeba histolytica — a protozoan parasite transmitted fecal-orally through contaminated food, water and close personal contact. Most infections (approximately 90%) are asymptomatic or caused by the non-pathogenic E. dispar. Approximately 10% of E. histolytica infections cause disease: amoebic colitis (bloody diarrhoea, abdominal cramps) or — rarely — amoebic liver abscess, the most common extraintestinal parasitic disease in humans.

How does amoebic liver abscess present?

Amoebic liver abscess (ALA) typically affects young to middle-aged men in endemic areas. Classical presentation: fever (often high, spiking); right upper quadrant pain or tenderness (sometimes radiating to the right shoulder from diaphragmatic irritation); liver enlargement; weight loss and malaise. Laboratory: elevated liver enzymes, leukocytosis, elevated CRP/ESR. Serology: anti-amoeba IgG positive in >95% (the key diagnostic test for ALA). Ultrasound: hypoechoic round mass in the right lobe. Note: simultaneous amoebic colitis is only present in approximately 30% of ALA cases — absence of diarrhoea does NOT exclude ALA.

How is amoebiasis treated?

Invasive amoebiasis (colitis or liver abscess): metronidazole 750mg three times daily × 7-10 days (IV if severe, oral if mild-moderate). This kills tissue trophozoites. MUST be followed by a luminal agent to clear intestinal cysts: diloxanide furoate (500mg TDS × 10 days) or paromomycin (25-35mg/kg/day in 3 doses × 7 days). Metronidazole alone has a significant relapse rate from persistent intestinal cysts. Liver abscess drainage: reserved for very large abscesses (>10cm), left lobe abscesses (rupture risk into pericardium), impending rupture, or failure of medical treatment — not routinely needed.

How is amoebiasis distinguished from IBD?

Amoebiasis can closely mimic inflammatory bowel disease (IBD — Crohn's disease, ulcerative colitis) clinically and endoscopically — both cause bloody diarrhoea, abdominal pain and mucosal inflammation. Critical importance: if IBD treatment (corticosteroids, biologic therapy) is given to a patient who actually has amoebic colitis, it can cause life-threatening amoebic dissemination. Before starting immunosuppression for suspected IBD: always test for E. histolytica (stool antigen or PCR). Key differences: amoebiasis serology positive; flask-shaped discrete ulcers; responds rapidly to metronidazole.

Is amoebiasis an STI?

E. histolytica is increasingly recognised as sexually transmitted in men who have sex with men (MSM) — through anal-oral sexual contact. Clusters of amoebiasis have been reported among MSM in Japan, Taiwan and Western cities. Most MSM-associated E. histolytica infections are asymptomatic or cause mild GI symptoms; invasive liver abscess is less common than in heterosexual tropical exposure. WHO recommends E. histolytica antigen testing (rather than serology) for asymptomatic MSM.

How does GMJ News cover amoebiasis?

GMJ News covers WHO amoebiasis burden data, amoebic liver abscess recognition, metronidazole treatment plus luminal agent, IBD vs amoebiasis distinction, MSM transmission, and NTD status. Amoebiasis is important in clinical differential diagnosis in Georgia — any returning traveller or migrant with liver mass or bloody diarrhoea should be assessed for E. histolytica.

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Amoebiasis

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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Amoebiasis — caused by Entamoeba histolytica — infects approximately 50 million people symptomatically per year and kills an estimated 40,000-100,000 annually, predominantly in tropical and subtropical LMICs, causing the classical clinical syndromes of amoebic colitis (bloody diarrhoea with characteristic flask-shaped ulcers) and amoebic liver abscess — the most common extraintestinal parasitic disease of humans (WHO). Amoebic liver abscess — typically a single large right-lobe abscess in adult men with fever, right upper quadrant pain and elevated liver enzymes — responds dramatically to metronidazole, which is both the clinical treatment and a satisfying demonstration of targeted antiparasitic therapy. Amoebiasis is a WHO Neglected Tropical Disease.

Key messages

50 million symptomatic infections — liver abscess

Amoebiasis causes approximately 50 million symptomatic infections and 40,000-100,000 deaths per year — with amoebic liver abscess (ALA) being the most common extraintestinal parasitic disease in humans. WHO NTD (WHO).

Only E. histolytica causes disease

Approximately 90% of Entamoeba infections are caused by the morphologically identical but non-pathogenic E. dispar or non-invasive E. histolytica. Molecular diagnosis distinguishing E. histolytica from E. dispar prevents unnecessary treatment.

Classic amoebic liver abscess

ALA — a single, right-lobe liver abscess in a middle-aged man with fever, right upper quadrant pain and elevated liver enzymes — responds dramatically to metronidazole. It is one of the most satisfying diagnoses in tropical medicine: antibody serology positive, ultrasound confirmation, dramatic clinical response.

Flask-shaped ulcers — amoebic colitis

Invasive amoebic colitis causes profuse bloody diarrhoea with characteristic flask-shaped ulcers on colonoscopy (wide mouth, undermined edges — from lateral spread beneath intact mucosa). Must be distinguished from inflammatory bowel disease.

Metronidazole then luminal agent

Treatment: metronidazole (tissue amoebiasis) followed by a luminal agent (diloxanide furoate, paromomycin) to eradicate cysts in the intestinal lumen. Metronidazole alone leaves cysts that cause recurrence.

Sexual transmission in MSM

E. histolytica is increasingly recognised as sexually transmitted in MSM — through anal-oral contact. Testing for amoebiasis in MSM with GI symptoms is recommended.

Key statistics

~50M

symptomatic amoebiasis cases/year

WHO

40-100K

amoebiasis deaths/year

WHO

90%

of E. histolytica infections are asymptomatic or non-invasive E. dispar

WHO

Right lobe

amoebic liver abscess predominantly affects right lobe (70-80% of cases)

WHO/Clinical

WHO NTD

amoebiasis is on the WHO Neglected Tropical Diseases list

WHO

90%

response rate to metronidazole in amoebic liver abscess

WHO/Cochrane

Amoebiasis global burden — symptomatic cases by clinical form (WHO)

Source: WHO. Liver abscess represents a minority of cases but carries the highest morbidity.

Glossary of key terms

Entamoeba histolytica
WHOThe only Entamoeba species definitively pathogenic in humans. Morphologically identical to E. dispar (non-pathogenic) and E. moshkovskii — molecular methods (antigen detection ELISA, PCR) are required for definitive species identification. Life cycle: trophozoites (active, motile — invasive form) and cysts (dormant — infectious form transmitted fecal-orally).

Amoebic liver abscess (ALA)
WHO/ClinicalThe most common extraintestinal complication of E. histolytica — affecting the liver parenchyma (predominantly the right lobe). Typically: single abscess; male > female (5:1); ages 20-50; contents are chocolate-brown "anchovy paste" liquid (lysed hepatocytes). Classical presentation: fever, right upper quadrant pain, weight loss, elevated liver enzymes, positive serology. Responds to metronidazole in >90% of cases.

Metronidazole
WHO EMLThe drug of choice for invasive amoebiasis — including amoebic colitis and liver abscess. Metronidazole 750mg three times daily × 7-10 days kills trophozoites. It does not adequately eradicate intestinal cysts — a luminal agent (diloxanide furoate 500mg TDS × 10 days, or paromomycin) must follow to prevent relapse and ongoing transmission.

Flask-shaped ulcer
WHO/PathologyThe characteristic endoscopic finding of invasive amoebic colitis — discrete ulcers with a narrow neck opening into the intestinal lumen but spreading laterally beneath the intact mucosa (undermined edges), creating a flask or bottle shape in cross-section. This pattern reflects amoebic trophozoites tunnelling through the mucosa while sparing the epithelial surface.

Antigen detection vs microscopy
WHOStool microscopy cannot reliably distinguish E. histolytica from E. dispar (morphologically identical). E. histolytica-specific antigen detection ELISA (or PCR) is the recommended test for diagnosis — it specifically identifies pathogenic E. histolytica. Serology (anti-amoeba IgG) is positive in invasive disease (especially ALA) but not in asymptomatic colonisation.

Amoeboma
WHO/ClinicalA rare granulomatous mass in the colon or caecum caused by chronic E. histolytica infection — clinically mimicking colorectal carcinoma (palpable abdominal mass, weight loss, altered bowel habit). Diagnosed by biopsy; responds to metronidazole.

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