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Organism

  • Protozoan- Entamoeba histolytica
  • Incubation: days-years

Transmission

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

Epidemiology

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

Pathogenesis

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

Complications

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

Diagnosis

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

Treatment

Metronidazole
Diloxanide furoate (after metronidazole to destroy gut cysts)

Prevention

Sanitation and good personal hygiene

 

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