Amoebiasis is caused by Entamoeba histolytica (an amoeboid protozoan) and spread by the faecal-oral route.

It is estimated that 10% of the world's population is chronically infected.

Infection can be asymptomatic, cause mild diarrhoea or severe amoebic dysentery. Amoebiasis also causes liver and colonic abscesses.

Amoebic dysentery

• profuse, bloody diarrhoea
• there may be a long incubation period
• stool microscopy may show trophozoites if examined within 15 minutes or kept warm (known as a 'hot stool')
• treatment is with metronidazole

Amoebic liver abscess

• usually a single mass in the right lobe (may be multiple). The contents are often described as 'anchovy sauce'
• features: fever, RUQ pain
• serology is positive in > 90%

Treatment for invasive amoebiasis should be followed by a luminal amoebicide to eradicate the cystic stage which is resistant to metronidazole and tinidazole (which are used against the invasive stage).