Parasites - Amebiasis (also known as Entamoeba histolytica infection)
What is amebiasis?
Amebiasis is a disease caused by a one-celled parasite called Entamoeba histolytica.
Who is at risk for amebiasis?
Although anyone can have this disease, it is more common in people who live in tropical areas with poor sanitary conditions. In the United States, amebiasis is most common in:
- People who have traveled to tropical places that have poor sanitary conditions
- Immigrants from tropical countries that have poor sanitary conditions
- People who live in institutions that have poor sanitary conditions
- Men who have sex with men
How can I become infected with E. histolytica?
E. histolytica infection can occur when a person:
- Puts anything into their mouth that has touched the feces (poop) of a person who is infected with E. histolytica.
- Swallows something, such as water or food, that is contaminated with E. histolytica.
- Swallows E. histolytica cysts (eggs) picked up from contaminated surfaces or fingers.
What are the symptoms of amebiasis?
Only about 10% to 20% of people who are infected with E. histolytica become sick from the infection. The symptoms are often quite mild and can include loose feces (poop), stomach pain, and stomach cramping. Amebic dysentery is a severe form of amebiasis associated with stomach pain, bloody stools (poop), and fever. Rarely, E. histolytica invades the liver and forms an abscess (a collection of pus). In a small number of instances, it has been shown to spread to other parts of the body, such as the lungs or brain, but this is very uncommon.
If I swallowed E. histolytica, how quickly would I become sick?
Only about 10% to 20% of people who are infected with E. histolytica become sick from the infection. Those people who do become sick usually develop symptoms within 2 to 4 weeks, though it can sometimes take longer.
What should I do if I think I have amebiasis?
See your health care provider.
How is amebiasis diagnosed?
Your health care provider will ask you to submit fecal (poop) 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 ameba, 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 does not make 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 but is only recommended when your health care provider thinks that your infection may have spread beyond the intestine (gut) to some other organ of your body, such as the liver. However, this blood test may not be helpful in diagnosing your current illness because the test can be positive if you had amebiasis in the past, even if you are no longer infected now.
How is amebiasis treated?
Several antibiotics are available to treat amebiasis. Treatment must be prescribed by a physician. You will be treated with only one antibiotic if your E. histolytica infection has not made you sick. You probably will be treated with two antibiotics (first one and then the other) if your infection has made you sick.
I am going to travel to a country that has poor sanitary conditions. What should I eat and drink there so I will NOT become infected with E. histolytica or other such germs?
The following items are safe to drink:
- Bottled water
- Tap water that has been boiled for at least 1 minute
- Carbonated (bubbly) water from sealed cans or bottles
- Carbonated (bubbly) drinks (like soda) from sealed cans or bottles
*You can also make tap water safe for drinking by filtering it through an "absolute 1 micron or less" filter and dissolving chlorine, chlorine dioxide, or iodine tablets in the filtered water. "Absolute 1 micron" filters can be found in camping/outdoor supply stores.
More on: Guide to Water Filters
The following items are NOT safe to drink or eat:
- Fountain drinks or any drinks with ice cubes
- Fresh fruit or vegetables that you did not peel yourself
- Milk, cheese, or dairy products that may not have been pasteurized.
- Anything sold by street vendors
Should I be concerned about spreading the infection to others?
Yes, but the risk of spreading infection is low if the infected person is treated with antibiotics and practices good personal hygiene. This includes thorough handwashing with soap and warm water after using the toilet, after changing diapers, and before handling food.
More on: Handwashing and Nail Hygiene
This information 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 parasites described above or think that you may have a parasitic infection, consult a health care provider.