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  • Protozoan- Entamoeba histolytica
  • Incubation: days-years


Faecal-oral (usually contaminated water): infection by ingestion of 4-nucleated cysts.


Humans are the only reservoir
10% world population are infected (rare in temperate climates)


Cyst is digested in gut releasing trophozoites (active parasites) which can colonise and invade colonic mucosa and cause cell lysis and ulcerations. Trophozoites may remain in the bowel or invade extra-intestinal tissues leaving ‘flask-shaped ulcers’. Cysts pass in the stools of carriers indefinitely and are viable for up to 2 months.

Amoebiasis life cycle
[image from wikipedia]

Clinical features

Leads to bloody diarrhoea, abdo pains and pyrexia (over period of 3 weeks)
Presentation may vary between:
  • asymptomatic (90%)
  • mild diarhoea
  • severe amoebic dysentery


Fulminant colitis (in immunosuppressed, elderly or pregnant)
Amoeboma- inflammatory mass, usually ileocaecal
Amoebic liver abscess
Chronic amoebiasis – intermittent non-bloody mucoid diarrhoea


Motile amoeba seen in fresh stool
Faecal antigen detection
US/CT = aspiration may confirm amoebic liver abscess
Positive serology


Diloxanide furoate (after metronidazole to destroy gut cysts)


Sanitation and good personal hygiene


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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