DefinitionAmebiasis is an infection of the intestines caused by the parasite Entamoeba histolytica.
Alternative NamesAmebic dysentery; Intestinal amebiasis
Causes, incidence, and risk factorsEntamoeba 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:AlcoholismCancerMalnutritionOlder or younger agePregnancyRecent travel to a tropical regionUse of corticosteroid medication to suppress the immune systemIn 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.
SymptomsMost 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 crampsDiarrhea
Passage of 3 - 8 semiformed stools per dayPassage of soft stools with mucus and occasional bloodFatigueExcessive gasRectal pain while having a bowel movement (tenesmus)Unintentional weight lossSevere symptoms:Abdominal tendernessBloody stoolsPassage of liquid stools with streaks of bloodPassage of 10 - 20 stools per dayFeverVomiting
Signs and testsExamination of the abdomen may show liver enlargement or tenderness in the abdomen.Tests include:Blood test for amebiasisExamination of the inside of the lower large bowel (sigmoidoscopy)Stool testMicroscope examination of stool samples, usually over several days
TreatmentTreatment 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.
ComplicationsLiver abscessMedication side effects, including nausea
Spread of the parasite through the blood to the liver, lungs, brain, or other organs
Calling your health care providerCall your health care provider if you have persistent diarrhea.
PreventionWhen 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.
ReferencesPetri 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.