Waterborne Diseases

Amebiasis is a disease caused by a one-celled parasite called Entamoeba histolytica.

It is most common in people who live in developing countries that have poor sanitary conditions,in people who have traveled to developing countries and in people who live in institutions that have poor sanitary conditions.

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Infection is acquired by the fecal-oral route, either by person-to-person contact or indirectly by drinking or eating fecally contaminated water or food
By putting anything into your mouth that has touched the stool of a person who is infected with E. histolytica. 
By swallowing something, such as water or food, that is contaminated with E. histolytica. 
By touching and bringing to your mouth cysts (eggs) picked up from surfaces that are contaminated with E. histolytica. 

The clinical spectrum of intestinal amebiasis ranges from asymptomatic infection to fulminant colitis. A newly recognized species, Entamoeba dispar, cannot be distinguished from E. histolytica by routine diagnostic methods. This organism appears to be responsible for asymptomatic infections. In infected persons who are symptomatic,the most common symptom is diarrhea. The diarrhea may evolve to painful, bloody bowel movements, with or without fever (amebic dysentery). Occasionally, amebiasis causes disease outside the intestines, most notably in the liver (amebic liver abscess). Even less commonly, it spreads to other parts of the body, such as the lungs or brain.

Usually 1 to 4 weeks later but sometimes more quickly or more slowly.

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See your health care provider.

Your health care provider will ask you to submit stool samples. Because E. histolytica is not always found in every stool sample, you may be asked to submit several stool samples from several different days.
Diagnosis of amebiasis can be very difficult. One problem is that other parasites and cells can look very similar to E. histolytica when seen under a microscope. Therefore, sometimes people are told that they are infected with E. histolytica even though they are not. Entamoeba histolytica and another amoeba, Entamoeba dispar, which is about 10 times more common, look the same when seen under a microscope. Unlike infection with E. histolytica, which sometimes makes people sick, infection with E. dispar never makes people sick and therefore does not need to be treated.
If you have been told that you are infected with E. histolytica but you are feeling fine, you might be infected with E. dispar instead. Unfortunately, most laboratories do not yet have the tests that can tell whether a person is infected with E. histolytica or with E. dispar. Until these tests become more widely available, it usually is best to assume that the parasite is E. histolytica.
A blood test is also available. However, the test is recommended only when your health care provider thinks that your infection has invaded the wall of the intestines (gut) or some other organ of your body, such as the liver. One problem is that the blood test may still be positive if you had amebiasis in the past, even if you are no longer infected now.

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Several antibiotics are available to treat amebiasis. Treatment must be prescribed by a physician.
No vaccine is available.

Travelers to developing countries are advised to follow the precautions included under "Risks From Food and Drink For travelers to developing countries". Risk of infection is highest for those who live in or visit rural areas, trek in backcountry areas, or eat or drink in settings of poor sanitation.

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This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.