Encyclopedia / A / Amebiasis



Amebiasis is an infection of the intestine, liver, or other tissues by pathogenic amebas (protozoan parasites).


Infection is typically by the organism Entamoeba histolytica, acquired by ingesting food or water contaminated by infected feces.

Entamoeba histolytica is an ameba, a type of single-celled animal that multiplies by simple division and moves around in the intestine, scavenging for small morsels of food and bacteria.

People can have the ameba in their intestines and excrete amebic cysts, but have no symptoms.

Most cases of amebiasis have very mild symptoms or none.

More severe infection may cause fever, profuse diarrhea, abdominal pain, jaundice, anorexia, and weight loss.

In severe cases, it can lead to development of abscesses (pockets of amebae and inflammatory cells) in the liver or, more rarely, the brain.


Amebiasis is most prevalent in tropical and subtropical countries where standards of public hygiene and sanitation may be low.

Most cases in the U.S. and other developed countries occur among travelers who have recently returned from developing tropical or subtropical countries. About 5,000 to 10,000 cases are diagnosed each year in the U.S., leading to about 20 deaths annually. It is most serious in infants, the elderly, and debilitated people.

Transmission generally occurs through ingestion of cysts from food or water contaminated by feces. All household members should have their stools examined because person to person transmission can occur.


Some strains of amebae are harmless but others, for unknown reasons, invade the intestinal wall, causing mucus secretion into the intestines and diarrhea - an illness called amebic dysentery. Additional symptoms may include fever, and abdominal cramping and pain.

In severe cases, ulcers may form in the intestinal wall; the amebae gain access to the bloodstream and travel to the liver to form abscesses.


Diagnostic tools may include:

  • Medical history, physical examination, lab tests, and stool studies
  • Blood tests for revealing antibodies to the organism
  • Sigmoidoscopy to evaluate the intestinal wall
  • Radiological studies including ultrasound and CT (computed tomography) scans to detect liver abscesses


The choice of drug depends on the type of clinical presentation and the site of drug action (in the intestinal wall versus inside the intestine itself). Drugs may include metronidazole, paromomycin, iodoquinol, or diloxanide furoate. These drugs have side effects that your physician can discuss with you.

Occasionally, it may be necessary to drain a liver abscess.

Follow-up care includes stool studies 2 to 4 weeks after completing treatment.


Do any other tests need to be done to determine the extent of involvement?

What kind of treatment will you be recommending?

Will you be prescribing any medication? What are the side effects?

Has the liver been affected?

If exploratory surgery or drainage of a liver abscess is recommended, what are the risks?

Is this condition contagious?

What precautions should be taken?

Travelers to countries where sanitary standards are low can reduce their chances of acquiring amebiasis by:

  • Drinking only water that has been bottled in sanitary conditions or boiled (water-purifying tablets are ineffective against amebic cysts)
  • Eating only cooked or peeled vegetables or fruits
  • Protecting food from fly contamination
  • Washing hands after defecation and before preparing or eating food