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

Causes

E histolytica can live in the large intestine (colon) without causing damage to the intestine. In some cases, it invades the colon wall, causing colitis, acute dysentery, or long-term (chronic) diarrhea. The infection can also spread through the bloodstream to the liver. In rare cases, it can spread to the lungs, brain, or other organs.

Colitis

Colitis is swelling (inflammation) of the large intestine (colon).

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This condition occurs worldwide. It is most common in tropical areas that have crowded living conditions and poor sanitation. Africa, Mexico, parts of South America, and India have major health problems due to this condition.

The parasite may spread:

• Through food or water contaminated with stool
• Through fertilizer made of human waste
• From person to person, particularly by contact with the mouth or rectal area of an infected person

Risk factors for severe amebiasis include:

• Alcohol use
• Cancer
• Malnutrition
• Older or younger age
• Pregnancy
• Recent travel to a tropical region
• Use of corticosteroid medicine to suppress the immune system

In the United States, amebiasis is most common among those who live in institutions or people who have traveled 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 may include:

• Abdominal cramps
• Diarrhea: passage of 3 to 8 semiformed stools per day, or passage of soft stools with mucus and occasional blood
• Fatigue
• Excessive gas
• Rectal pain while having a bowel movement (tenesmus)

  Tenesmus

  Tenesmus is the feeling that you need to pass stools, even though your bowels are already empty. It may involve straining, pain, and cramping....

  

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• Unintentional weight loss

  Unintentional weight loss

  Unexplained weight loss is a decrease in body weight, when you did not try to lose the weight on your own. Many people gain and lose weight. Uninten...

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Severe symptoms may include:

• Abdominal tenderness
• Bloody stools, including passage of liquid stools with streaks of blood, passage of 10 to 20 stools per day

  Bloody stools

  Black or tarry stools with a foul smell are a sign of a problem in the upper digestive tract. It most often indicates that there is bleeding in the ...

  

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• Fever
• Vomiting

Exams and Tests

The health care provider will perform a physical exam. You will be asked about your medical history, especially if you have recently traveled overseas.

Examination of the abdomen may show liver enlargement or tenderness in the abdomen (typically in the right upper quadrant).

Liver enlargement

Enlarged liver refers to swelling of the liver beyond its normal size. Hepatomegaly is another word to describe this problem. If both the liver and ...

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Tests that may be ordered include:

• Blood test for amebiasis
• Examination of the inside of the lower large bowel (sigmoidoscopy)

  Sigmoidoscopy

  Sigmoidoscopy is a procedure used to see inside the sigmoid colon and rectum. The sigmoid colon is the area of the large intestine nearest to the re...

  

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• Stool test
• Microscope examination of stool samples, usually with multiple samples over several days

  Microscope examination of stool samples

  Stool ova and parasites exam is a lab test to look for parasites or eggs (ova) in a stool sample. The parasites are associated with intestinal infec...

  

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Treatment

Treatment depends on how severe the infection is. Usually, antibiotics are prescribed.

If you are vomiting, you may be given medicines 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 antibiotic treatment, your stool will likely be rechecked to make sure the infection has been cleared.

Outlook (Prognosis)

Outcome is usually good with treatment. Usually, the illness lasts about 2 weeks, but it can come back if you do not get treated.

Possible Complications

Complications of amebiasis may include:

• Liver abscess (collection of parasites and pus in the liver)

  Liver abscess

  Amebic liver abscess is a collection of pus in the liver in response to an intestinal parasite called Entamoeba histolytica.

  

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

When to Contact a Medical Professional

Contact your provider if you have diarrhea that does not go away or gets worse.

Prevention

When traveling in countries where sanitation is poor, drink purified or boiled water. Do not eat uncooked vegetables or unpeeled fruit. Wash your hands after using the bathroom and before eating.

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