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Amebiasis

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

Alternative Names

Amebic dysentery; Intestinal amebiasis

Causes, incidence, and risk factors

Entamoeba histolytica can live in the large intestine (colon) without causing damage to the instestins. 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 occurs worldwide, 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 contamination 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
  • Older or younger 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 or people who have returned from travel to an area where amebiasis is common.

Symptoms

Most people with this infection do not have symptoms. If symptoms occur, they are seen 7 to 28 days after being exposed to the parasite.

Mild symptoms:

  • Abdominal cramps
  • Diarrhea
    • Passage of 3 - 8 semiformed stools per day
    • Passage of soft stools with mucus and occasional blood
  • Fatigue
  • Excessive gas
  • 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

Signs and tests

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

Tests include:

  • Blood test for amebiasis
  • Examination of the inside of the lower large bowel (sigmoidoscopy )
  • Stool test
  • Microscope examination of stool samples, usually over several days

Treatment

Treatment depends on the severity of infection. Usually, metronidazole is given by mouth for 10 days. This is followed by paromomycin or diloxanide.

If you are vomiting, you may need to medications through a vein (intravenously ) until you can take them by mouth. Medicines to stop diarrhea are usually not prescribed because they can make the condition worse.

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

Expectations (prognosis)

The outcome is usually good with treatment. Usually, the illness lasts about 2 weeks, but it can come back if treatment is not given.

Complications

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

Calling your health care provider

Call your health care provider if you have persistent diarrhea.

Prevention

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.

References

Petri WA Jr, Haque R. Amebiasis. In: Goldman L, Schafer AI,eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 360.

Petri WA Jr, Haque R. Entamoeba species, including amebiasis.In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 273.

Updated: 8/15/2012

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


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