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 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.

The bacteria 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.

Intestinal amebiasis causes frequent diarrhea, often with abdominal pain. Rectal pain during the diarrhea (tenesmus ) is also common. The diarrhea may contain blood or mucus. Usually, the illness lasts about 2 weeks, but it can come back again and again if not treatment is given.

Risk factors for severe amebiasis include malnutrition, old age, pregnancy, use of steroids, malignancy (cancer), and alcoholism. Recent travel to a tropical region is also a risk factor.

In the United States, amebiasis is most common among those who live in institutions and people who have anal intercourse. There are an estimated 50 million cases worldwide of amebiasis with 40,000 to 50,000 deaths annually.

Mild symptoms:

• Diarrhea
  • Passage of 3 to 8 semiformed stools per day
  • Passage of soft stools with mucus and occasional blood
• Abdominal cramps
• Fatigue
• Unintentional weight loss
• Intestinal gas (excessive flatus )

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

Examination of the abdomen may show liver enlargement and abdominal tenderness.

Tests include:

• Stool culture of 3 stool specimens several days apart
• Serology for amebiasis
• Sigmoidoscopy

Oral antiparasitic medication is the standard treatment for amebiasis. The choice of drug depends on the severity of the infection.

When the patient is vomiting, intravenous therapy may be necessary until medications can be tolerated by mouth. Antidiarrheal medications are usually not prescribed and can make the condition worse.

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

The outcome is likely to be 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 persistent diarrhea occurs.

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.