Amebiasis is an infection caused by amebas or protozon, especially Entamoeba histolytica. It initially involves the intestine following the consumption of contaminated food or water.

Most often, the infected host experiences no symptoms and the infection clears within eight to 12 months. While dwelling in the intestine of the host, the amoeba multiplies, living off of bacteria, food residues, blood cells, and other tissue. Some of these parasites form hard, acid-resistant shells or cysts around themselves. When excreted, these cysts can survive for lengthy periods and are not easily destroyed by hostile environments or water purification systems.

If water or food is contaminated with cysts (common in countries where human waste is used as fertilizer), infection may spread. Rare in the United States, amebiasis infects as many as half the inhabitants of some underdeveloped countries.

Serious complications include the formation of a liver abscess that can then rupture into the abdominal cavity (peritonitis), the pleural membranes covering the lungs, or the tissues surrounding the heart (pericarditis). In rare cases, infection may spread via the bloodstream to the lungs or brain.

Amebiasis usually responds quickly and completely to therapy. Relapse and fatality are unlikely with proper treatment, though in developing countries reinfection is common.

What Causes Amebiasis?

  • Infection occurs from ingestion of the fecally excreted, acid-resistant, cystic form of the amoeba. Transmission commonly results from fecal contamination of water or food, which is most prevalent in regions with poor sanitary conditions. Another mode of transmission is oral sex preceded by anal sex.
  • At highest risk for severe illness from amebiasis are those who are malnourished; under two years of age; receiving corticosteroid therapy; pregnant; or who have compromised immune systems.

Symptoms of Amebiasis

  • Diarrhea, possibly containing blood or mucus
  • Rectal pain during bowel movements (tenesmus)
  • Intestinal gas (excessive flatulence)
  • Severe abdominal cramping and tenderness
  • Excessive gas
  • Loss of weight
  • High fever
  • Fatigue
  • Nausea and vomiting (with liver abscess)


  • When visiting underdeveloped countries, drink only boiled or purified water (chlorine is ineffective against amoebic cysts; water treated with iodine or globaline tablets is safe, however). In addition, do not eat uncooked vegetables (especially leafy greens, which are often fertilized with human waste) or fruit that is already sliced or peeled. Immunization is not available.
  • Always wash hands thoroughly with soap and warm water after using the toilet, after changing diapers, before preparing food or drink, and before eating.
  • Drink only pasteurized milk and dairy products.
  • Practice safer sex, including using condoms for anal contact and dental dams for oral contact to help prevent infection.


  • Patient history and physical examination are needed.
  • Confirmation of the diagnosis requires identification of E. histolytica in stool or tissue samples.
  • Blood tests may be done to look for antibodies to the parasite.
  • An abdominal ultrasound scan may be performed to check for liver abscess.
  • Sigmoidoscopy (use of a lighted rectal scope) and a barium enema (use of barium to create a clear image of the intestine on x-ray) may be done to rule out other disorders of the colon that can mimic or occur in conjunction with amebiasis. Tissue biopsies from sigmoidoscopy are sometimes needed to confirm the presence of the amoeba.

How to Treat Amebiasis

  • Replacement of fluids, electrolytes (mineral salts), and blood may be needed.
  • Standard treatment includes oral antiparasitic medication.
  • Several drugs (including diloxanide furoate, tinidazole, iodoquinol, and metronidazole) are used to eliminate the amoeba. Metronidazole is most often used to treat symptomatic disease; iodoquinol helps eradicate cysts in patients with no symptoms.
  • A liver abscess may be treated with needle aspiration (removal of pus with a syringe) or may require surgical drainage.

When to Call a Doctor

  • Call a doctor for persistent or recurrent diarrhea.


Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference

Simeon Margolis, M.D., Ph.D., Medical Editor

Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 23 Aug 2011

Last Modified: 22 Sep 2015