Amoebiasis

Description

Amoebiasis is caused by the protozoan parasite Entamoeba histolytica. Infection is acquired by the faecal-oral route, either by person-to-person contact or indirectly by eating or drinking faecally contaminated food or water.

Occurrence

Amoebiasis occurs worldwide, especially in regions with poor sanitation. E. histolytica antibody prevalence rates (reflecting past or recent infection), commonly range from 6% to 25% in developing countries, but may exceed 50% in some communities.

Risk for Travellers

For travellers to developing countries, risk for infection is highest for those who live in or visit rural areas, spend time in backcountry areas, or eat or drink in settings of poor sanitation.

Clinical Presentation

The incubation period is commonly 2-4 weeks but ranges from a few days to years. The clinical spectrum of intestinal amoebiasis ranges from asymptomatic infection to fulminant colitis and peritonitis. The parasite initially infects the colon, but it occasionally may spread to other organs, most commonly the liver (amebic liver abscess). In persons infected with E. histolytica who are symptomatic, the most common symptom is diarrhoea. The diarrhoea can worsen to painful, bloody bowel movements, with or without fever (amebic dysentery). Entamoeba dispar, a nonpathogenic amoeba that also inhabits the colon, cannot be distinguished from the pathogen E. histolytica by routine microscopy; however, an enzyme immunoassay kit for distinguishing the two organisms in fresh stool specimens is commercially but not widely available. Similarly, polymerase chain reaction (PCR)-based diagnostic tests have been developed but are not widely available.

Prevention

No vaccine is available. Travellers to developing countries should be advised to follow the precautions detailed in the section Risks from Food and Water in Chapter 2 and avoid sexual practices that may lead to faecal-oral transmission.

Treatment

Travellers may be advised to consult with an infectious disease specialist to ensure proper diagnosis and treatment. Iodoquinol or paromomycin are the drugs of choice for asymptomatic but proven E. histolytica infections. For mild or moderate to severe intestinal disease and extraintestinal disease (e.g., hepatic abscess), treatment with metronidazole or tinidazole should be immediately followed by treatment with paromomycin or iodoquinol. E. dispar infection does not require treatment.

Bibliography
  • Ravdin JI, editor. amoebiasis. Human infection by Entamoeba histolytica. New York: John Wiley & Sons; 1988.
  • Ravdin JI. Entamoeba histolytica (amoebiasis). In: Mandell GL, Bennett JE, Dolin R, editors. Mandell, Douglas and Bennett's principles and practice of infectious diseases. 5th ed. Philadelphia, PA: Churchill Livingstone; 2000. p. 2798-810.
  • Sanuki JT, Asai E, Okuzawa S, et al. Identification of Entamoeba histolytica and E. dispar cysts in stool by polymerase chain reaction. Parasitol Res. 1997;83:96-8.
  • Tanyuksel M, Petri WA Jr. Laboratory diagnosis of amoebiasis. Clin Microbiol Rev. 2003;16:713-29.
  • Verweij JJ, Blotkamp J, Brienen A, et al. Differentiation of Entamoeba histolytica and Entamoeba dispar cysts using polymerase chain reaction on DNA isolated from faeces with spin columns. Eur J Clin Microbiol Infect Dis. 2000;19:358-61.

- Dennis Juranek

© Medic8 ® All Rights Reserved.