Amoebiasis

Amoebiasis is a parasitic infection due to the intestinal protozoa Entamoeba histolytica. Transmission is faecal-oral, by ingestion of amoebic cysts from food or water contaminated with faeces. Usually, ingested cysts release non-pathogenic amoebae and 90% of carriers are asymptomatic.
In 10% of infected patients, pathogenic amoebae penetrate the mucous of the colon: this is the intestinal amoebiasis (amoebic dysentery). The clinical picture is similar to that of shigellosis, which is the principal cause of dysentery.
Occasionally, the pathogenic amoebae migrate via the blood stream and form peripheral abscesses. Amoebic liver abscess is the most common form of extra-intestinal amoebiasis.

Clinical features

• Amoebic dysentery
  • diarrhoea containing red blood and mucus
  • abdominal pain, tenesmus
  • no fever or moderate fever
  • possibly signs of dehydration
• Amoebic liver abscess
  • painful hepatomegaly; mild jaundice may be present
  • anorexia, weight loss, nausea, vomiting
  • intermittent fever, sweating, chills; change in overall condition

Investigations

• Amoebic dysentery: identification of mobile trophozoites (E. histolytica histolytica) in fresh stool samples
• Amoebic liver abscess: indirect haemoagglutination and ELISA
• POCUS a Citation a. POCUS should only be performed and interpreted by trained clinicians. : perform an EFAST (extended focused assessment with sonography for trauma) examination, with additional views of the liver and spleen to evaluate for signs of amoebic lesions. Contact an expert (local or via telemedicine services) to help interpret the images and differentiate amoebic abscesses from other pathologies with similar characteristics.

Treatment

• Amoebic dysentery
  • The presence of cysts alone should not lead to the treatment of amoebiasis.
  • Amoebiasis confirmed with a parasitological stool examination: 
    tinidazole PO
    Children: 50 mg/kg once daily for 3 days (max. 2 g daily)
    Adults: 2 g once daily for 3 days
    or metronidazole PO
    Children: 15 mg/kg 3 times daily for 5 days
    Adults: 500 mg 3 times daily for 5 days
  • If there is no laboratory, first line treatment for dysentery is for shigellosis. Treat for amoebiasis if correct treatment for shigellosis has been ineffective.
  • Oral rehydration salts (ORS) if there is risk of, or if there are signs of dehydration (see Dehydration, Chapter 1).
• Amoebic liver abscess
  • tinidazole PO: same treatment for 5 days
  • metronidazole PO: same treatment for 5 to 10 days