Amoebic Colitis

Amoebic colitis (amoebic dysentery) is invasion of the colonic mucosa by Entamoeba histolytica, acquired through faeco oral transmission by contaminated water, food or poor sanitation. It is common in Kenyan informal settlements and among travellers.

• Risk factors: poor sanitation, malnutrition, HIV, alcohol use, corticosteroid use, pregnancy, institutional living, men who have sex with men.
• Trophozoites invade the caecum, ascending and sigmoid colon, forming flask shaped ulcers.

Gradual onset over 1 to 3 weeks of bloody mucoid diarrhoea, cramping, tenesmus, low grade fever and weight loss.

• Fulminant colitis with high fever, profuse bloody diarrhoea, toxaemia, abdominal distension and perforation.
• Extraintestinal: liver abscess (right upper quadrant pain, fever, tender hepatomegaly), lung and brain involvement.
• Differential diagnosis: shigellosis, Campylobacter, Salmonella, enterohaemorrhagic E. coli, inflammatory bowel disease, ischaemic colitis, CMV colitis, schistosomiasis (S. mansoni), colon cancer, Clostridioides difficile, appendicitis, diverticulitis.
• Complications: toxic megacolon, perforation and peritonitis, haemorrhage, amoeboma, stricture, liver abscess, empyema, pericarditis, cutaneous amoebiasis, death.

Combine stool microscopy with antigen or PCR.

• Fresh stool: trophozoites with ingested red cells (diagnostic), cysts (cannot separate E. histolytica from non pathogenic species by microscopy); stool antigen or PCR for E. histolytica; three samples.
• Serology (positive in most invasive disease); colonoscopy with biopsy (flask shaped ulcers) when stool tests are negative or inflammatory bowel disease is possible.
• Full blood count, electrolytes, albumin, CRP; ultrasound for liver abscess; abdominal radiograph and CT for perforation.

Give a tissue active agent followed by a luminal agent.

• Supportive: oral rehydration solution or IV Ringer lactate for dehydration, nutrition, correction of electrolytes, analgesia (paracetamol 1 g; avoid opioids and anticholinergics), avoid antimotility drugs and corticosteroids.
• Pharmacological: metronidazole 750 mg orally three times daily for 7 to 10 days (children 35 to 50 mg/kg/day in 3 doses for 7 to 10 days), or tinidazole 2 g orally once daily for 3 days (children 50 mg/kg/day for 3 days); severe or fulminant disease: metronidazole 500 mg IV every 8 hours with ceftriaxone 2 g IV daily for enteric bacteria. Follow with a luminal agent to eliminate cysts: paromomycin 25 to 35 mg/kg/day in 3 doses for 7 days (adults 500 mg three times daily), or diloxanide furoate 500 mg three times daily for 10 days (children 20 mg/kg/day).
• Procedures: surgery for perforation, toxic megacolon or uncontrolled haemorrhage (resection with stoma, peritoneal lavage); percutaneous drainage for large or non responding liver abscess.
• Special groups: pregnancy, metronidazole after the first trimester (paromomycin first trimester); children, weight based dosing; HIV, prolonged disease and relapse more common; alcohol, avoid during and for 48 hours after metronidazole or tinidazole.
• Red flags: severe abdominal pain with distension, peritonism, high fever with toxaemia, haemodynamic instability, hepatic abscess signs, failure of response at 3 days.
• Follow-up: stool microscopy at 2 to 4 weeks; colonoscopy in persistent symptoms; advise on water, hygiene and food safety.