Amoebiasis: comprehensive intestinal colitis, liver abscess, diagnosis and management

Learning outcomes

• Describe cyst and trophozoite morphology and the faecal–oral life cycle.
• Explain adherence, flask-shaped ulcers, portal spread and liver abscess formation.
• Differentiate asymptomatic carriage, amoebic colitis, fulminant colitis and extraintestinal disease.
• Interpret stool microscopy, antigen/PCR, serology and liver imaging.
• Manage dysentery, liver abscess, complications and treatment failure safely.
• Prevent transmission through sanitation, water safety and sexual-health counselling.

Organism and life cycle

After cyst ingestion, excystation occurs in the small bowel. Trophozoites migrate to the caecum and colon, multiply and either remain luminal or invade. Encystation occurs during distal transit and cysts are passed in formed stool.

Transmission and risk factors

• Faecally contaminated water, food, hands and household surfaces.
• Inadequate sanitation, crowded institutions and unsafe sewage disposal.
• Oral–anal sexual exposure and household contact.
• Travel/residence in endemic tropical settings.
• Malnutrition, pregnancy, immunosuppression and corticosteroid exposure, which can worsen invasive disease.

Cysts are the major environmental and transmission form. Trophozoites in fresh diarrhoeal stool die quickly but may transmit directly during sexual contact.

Pathogenesis

E. histolytica uses lectin-mediated adherence to colonic mucin and epithelial cells, then releases proteases and cytotoxic molecules that damage cells and extracellular matrix. Initial mucosal lesions enlarge into characteristic flask-shaped ulcers with a narrow mucosal neck and broad submucosal base. Trophozoites can enter venules and travel through the portal system to the liver. The liver lesion contains necrotic material and inflammatory cells; it may be sterile initially but can become secondarily infected with bacteria.

Clinical spectrum

Asymptomatic intestinal infection

Many infected people pass cysts without symptoms. Confirmed E. histolytica carriage matters because transmission and future invasion are possible. A luminal eradication regimen is generally required, but a non-specific microscopy report should be clarified before labelling every Entamoeba as pathogenic.

Amoebic colitis

• Gradual abdominal pain, tenesmus and frequent loose stools.
• Mucus and blood ranging from mild dysentery to severe colitis.
• Weight loss, anorexia, fatigue and low-grade fever.
• Right iliac fossa tenderness or an amoeboma-like inflammatory mass.

Fulminant necrotising colitis

Extensive ulceration may cause severe pain, high fever, ileus, peritonism, toxic megacolon, perforation, massive haemorrhage, shock and death. Corticosteroids given for presumed inflammatory bowel disease can accelerate fulminant amoebiasis.

Amoebic liver abscess

• Fever, right-upper-quadrant pain and tender hepatomegaly.
• Referred right shoulder pain, pleuritic pain or cough from diaphragmatic irritation.
• Often solitary and right-lobe dominant, but multiple lesions occur.
• Jaundice, respiratory distress, pleural effusion or peritonism suggest obstruction or rupture.

Rupture may occur into the pleura, lung, pericardium, peritoneum or skin. Brain abscess is rare and rapidly life-threatening.

History and examination

Ask about water and sanitation, travel, household diarrhoea, oral–anal exposure, previous dysentery, recent antibiotics, steroid use, HIV/immunosuppression, weight loss and duration. For suspected liver abscess ask about RUQ/shoulder pain, cough, alcohol, biliary disease and prior treatment.

Assess hydration, pulse, blood pressure, fever, pallor, abdominal tenderness, guarding, distension, bowel sounds, hepatomegaly, jaundice, pleural signs, skin lesions and mental status. Toxic appearance, peritonism, shock, severe anaemia or altered consciousness requires admission and urgent specialist review.

Diagnosis and interpretation

Intestinal disease

• Specific stool antigen or PCR: preferred where available because it distinguishes E. histolytica from look-alikes.
• Fresh microscopy: may show trophozoites or cysts; rapid examination is important. Multiple specimens increase yield.
• Haematophagous trophozoites: a classic clue, but erythrophagocytosis is not perfectly specific and should not replace antigen/PCR.
• Endoscopy/biopsy: reserved for uncertainty, severe colitis or suspected inflammatory bowel disease/amoeboma; biopsy risks must be considered.

Extraintestinal disease

• Ultrasound: accessible first-line imaging for liver abscess.
• CT/MRI: defines size, number, rupture, pleural/peritoneal extension and alternative pathology.
• Serology: often positive in liver abscess but may remain positive after previous infection; interpret with imaging.
• Aspirate: may contain thick brown “anchovy-sauce” material; send for bacterial culture and amebic antigen/PCR where possible.

Differential diagnosis

For dysentery consider shigellosis, campylobacteriosis, salmonellosis, Yersinia, inflammatory bowel disease, intestinal tuberculosis, schistosomiasis, colorectal cancer and ischemic colitis. For liver lesions consider pyogenic abscess, hydatid disease, malignancy, tuberculosis, fungal abscess and infected biliary cysts. Amoebic and bacterial abscess may coexist.

Management of intestinal infection

• Use oral or IV fluids according to dehydration and ability to drink.
• Avoid loperamide and other antimotility drugs in severe bloody diarrhoea or suspected invasive colitis.
• Do not give corticosteroids for presumed IBD until amoebic colitis is excluded; if steroids were started, involve specialists urgently.
• Review pregnancy, breastfeeding, liver disease, drug interactions and alcohol use before nitroimidazole therapy.

Amoebic liver abscess

1. Obtain ultrasound and baseline FBC/LFTs; take blood cultures if febrile/toxic.
2. Start a tissue-active nitroimidazole promptly under UCG guidance.
3. Follow with a luminal agent after the tissue-active course.
4. Provide analgesia, fluids, nutrition and fever monitoring.
5. Consider image-guided aspiration/drainage for a very large lesion, left-lobe abscess, impending rupture, pleural/peritoneal extension, bacterial superinfection, diagnostic uncertainty or lack of improvement after several days.
6. Send aspirate for bacterial culture and amebic PCR/antigen where possible.
7. Manage rupture into pleura, lung, peritoneum or pericardium with interventional, surgical and respiratory teams.

Fulminant colitis and surgical complications

Admit patients with systemic toxicity, severe bleeding, ileus, peritonism, distension or suspected megacolon. Give broad supportive care, tissue-active antiamoebic therapy and antibiotics when bacterial translocation/sepsis is suspected. Obtain urgent surgical review for perforation, uncontrolled haemorrhage, toxic megacolon or necrotising colitis. Avoid colonoscopy in an unstable patient or when perforation is suspected.

Complications

• Fulminant necrotising colitis, toxic megacolon, perforation and haemorrhage.
• Amoeboma, strictures and recurrent colitis.
• Liver abscess rupture into pleura, lung, peritoneum or pericardium.
• Secondary bacterial infection, sepsis and respiratory failure.
• Rare brain, skin or genitourinary disease.

Prevention

• Safe water, sanitation and handwashing after toileting and before food preparation.
• Wash produce with safe water and avoid uncooked food prepared in unsafe conditions.
• Do not prepare food for others while experiencing diarrhoea.
• Use barrier protection and avoid oral–anal contact during diarrhoeal illness.
• Identify confirmed carriers through specific testing and treat according to UCG/public-health advice.
• Investigate household or institutional clusters and improve sewage disposal.

Exam and OSCE pearls

• E. histolytica invades; E. dispar usually does not.
• Flask-shaped ulcers and haematophagous trophozoites are classic but not substitutes for specific tests.
• Bloody diarrhoea with tenesmus suggests colitis; RUQ pain/hepatomegaly suggests liver abscess.
• Always follow metronidazole/tinidazole with a luminal agent.
• Worsening after corticosteroids is a red flag for unrecognised amoebiasis.
• Image the liver when fever and RUQ pain persist even if stool testing is negative.

References

• SlideShare: Amoebiasis.
• Uganda Clinical Guidelines: GI006.
• CDC: Amebiasis.
• CDC DPDx: Amebiasis diagnosis.
• MSD Manual Professional: Amebiasis.

Safety note: Confirm treatment, dose and drainage decisions against current UCG, local resistance patterns and specialist advice for severe colitis, pregnancy, children and liver abscess.