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Amebiasis is an infection of the intestines caused by the parasite Entamoeba histolytica.

Entamoeba histolytica can live in the large intestine (colon) without causing disease. However, sometimes, it invades the colon wall, causing colitis, acute dysentery, or long-term (chronic) diarrhea. The infection can also spread through the blood to the liver and, rarely, to the lungs, brain or other organs.

This condition can be seen anywhere in the world, but it is most common in tropical areas with crowded living conditions and poor sanitation. Africa, Mexico, parts of South America, and India have significant health problems associated with this disease.

Entamoeba histolytica is spread through food or water contaminated with stools. This is common when human waste is used as fertilizer. It can also be spread from person to person -- particularly by contact with the mouth or rectal area of an infected person.

Risk factors for severe amebiasis include:

• Alcoholism
• Cancer
• Malnutrition
• Old age
• Pregnancy
• Recent travel to a tropical region
• Use of corticosteroid medication to suppress the immune system

In the United States, amebiasis is most common among those who live in institutions and people who have anal intercourse.

Usually, the illness lasts about 2 weeks, but it can come back if treatment is not given.

Mild symptoms:

• Abdominal cramps
• Diarrhea
  • Passage of 3 - 8 semiformed stools per day
  • Passage of soft stools with mucus and occasional blood
• Fatigue
• Intestinal gas (excessive flatus)
• Rectal pain while having a bowel movement (tenesmus)
• Unintentional weight loss

Severe symptoms:

• Abdominal tenderness
• Bloody stools
  • Passage of liquid stools with streaks of blood
  • Passage of 10 - 20 stools per day
• Fever
• Vomiting

Note: In 90% of people with amebiasis there are no symptoms.

Examination of the abdomen may show liver enlargement or tenderness in the abdomen.

Tests include:

• Blood test for amebiasis (serology)
• Examination of the inside of the lower large bowel (sigmoidoscopy)
• Microscope examination of 3 stool specimens several days apart

Oral antiparasitic medication is the standard treatment for amebiasis. The choice of drug depends on the severity of the infection. Typically oral metronidaloze is used for 10 days.

If you are vomiting, you may need treatment through a vein (intravenous) until you can tolerate medications by mouth. Antidiarrheal medications are usually not prescribed because they can make the condition worse.

After treatment, the stool should be rechecked to ensure that the infection has been cleared.

The outcome is usually good with treatment.

• Liver abscess
• Medication side effects, including nausea
• Spread of the parasite through the blood to the liver, lungs, brain, or other organs

Call your health care provider if you have persistent diarrhea.

When traveling in tropical countries where poor sanitation exists, drink purified or boiled water and do not eat uncooked vegetables or unpeeled fruit. Public health measures include water purification, water chlorination, and sewage treatment programs.

Safer sex measures, such as the use of condoms and dental dams for oral or anal contact, may help prevent infection.

Amebic dysentery; Intestinal amebiasis

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Jatin M. Vyas, PhD, MD, Instructor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.