Amebiasis

Amebic brain abscess — Amebiasis, normally an infection of the intestinal tract, may spread and infect other organs such as the liver or brain. Infection of the brain can be fatal. In this slide, ameba are shown in a sample of brain tissue. Ameba represent a serious infection in immunocompromised individuals. (Image courtesy of the Centers for Disease Control and Prevention.)

Also known as: Amebic dysentery and Intestinal amebiasis

Definition

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

Causes, incidence, and risk factors

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 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
Malnutrition
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 and people who have anal intercourse.

Symptoms

Most people with this infection do not have symptoms If symptoms occur, they are seen 7 to 10 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)
Microscope examination of stool samples, usually several days apart

Treatment

Treatment depends on the severity of infection. Usually, metronidaloze is given by mouth for 10 days.

If you are vomiting, you may need to receive medications through a vein (intravenously) until you can tolerate them by mouth. Antidiarrheal medications 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.

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

References

Schuster FL, Glaser CA. Amebiasis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 373.

Review date:: September 15, 2010
Reviewed by:: 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., Inc.

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