Definition: Amebiasis is an infection of the intestines. It is caused by the microscopic parasite Entamoeba histolytica.
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.
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 stools
- 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
- Older or younger age
- Recent travel to a tropical region
- Use of corticosteroid medicine to suppress the immune system
In Canada and 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.
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
- Excessive gas
- Rectal pain while having a bowel movement (tenesmus)
- Unintentional weight loss
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
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.
Tests that may be ordered include:
- Blood test for amebiasis
- Examination of the inside of the lower large bowel (sigmoidoscopy)
- Stool test
- Microscope examination of stool samples, usually with multiple samples over several days
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.
Outcome is usually good with treatment. Usually, the illness lasts about 2 weeks, but it can come back if you do not get treated.
Complications of amebiasis may include:
- Liver abscess (collection of pus in the liver)
- Medicine 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 diarrhea that does not go away or gets worse.
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.
Petri WA, Lima AAM. Amebiasis. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 352.