Amebiasis is a parasitic infection of the intestines caused by the
protozoan Entamoeba histolytica, or E. histolytica. The symptoms of
amebiasis include loose stool, abdominal cramping, and stomach pain. However,
most people with amebiasis won’t experience significant symptoms.
Is at Risk for Amebiasis?
Amebiasis is common in tropical countries with underdeveloped
sanitation. The Merck
Manual states that amebiasis is most common in the Indian subcontinent,
parts of Central and South America, and parts of Africa. It’s relatively rare
in the United States.
Persons at greatest risk for amebiasis include:
- people who have traveled to tropical locations
with poor sanitation
- immigrants from tropical countries with poor sanitary
- people who live in institutions with poor
sanitary conditions, such as prisons
- men who have sex with other men
- people with compromised immune systems and other
E. histolytica is a
single-celled protozoan that usually enters the human body when a person
ingests cysts through food or water. It can also enter the body through direct
contact with fecal matter. The cysts are a relatively inactive form of the
parasite that can live for several months in the soil or environment where they
were deposited in feces. The microscopic cysts are present in soil, fertilizer,
or water that’s been contaminated with infected feces. Food handlers may
transmit the cysts while preparing or handling food. Transmission is also
possible during anal sex or colonic irrigation.
When cysts enter the body, they lodge in the digestive tract.
They then release an invasive form of the parasite called a trophozite. The
parasites reproduce in the digestive tract and migrate to the large intestine.
There, they can burrow into the intestinal wall or the colon. This causes
bloody diarrhea, colitis, and tissue destruction. The infected person can then
spread the disease by releasing new cysts into the environment through infected
Once the trophozites have breached the intestinal walls, they can
enter the bloodstream and travel to various internal organs. If they invade an
internal organ, they can potentially cause:
- severe illness
Are the Symptoms of Amebiasis?
When symptoms occur, they tend to appear one to four weeks after
ingestion of the cysts. According to the Centers for
Disease Control and Prevention (CDC), only about 10 to 20 percent of people
who have amebiasis become ill from it. Symptoms at this stage tend to be mild
and include loose stools and stomach cramping.
If the parasite invades the lining of your intestine, it can
produce amebic dysentery. Amebic dysentery is a more dangerous form of the
disease with frequent watery and bloody stools and severe stomach cramping. If
the parasite enters your bloodstream, it can end up in your liver, heart,
lungs, brain, or other organs, where it causes tissue destruction and
abscesses. The liver is a frequent destination for the parasite. Symptoms of
amebic liver disease include fever and tenderness in the upper-right part of
Is Amebiasis Diagnosed?
A doctor may suspect amebiasis after asking about your recent
health and travel history. Your doctor may test you for the presence of E. histolytica. You may have to give stool
samples over several days to screen for the presence of cysts. Your doctor may order
lab tests to check liver function, which can help determine if the ameba has
damaged your liver.
If damage to your internal organs is a concern, your doctor will
probably order an ultrasound or CT scan to check for lesions on your liver. If
lesions appear, your doctor may need to perform a needle aspiration to see if
the liver has any abscesses. An abscess in the liver is a serious consequence
Finally, a colonoscopy may be necessary to check for the presence
of the parasite in your intestinal or colon tissue.
Treatments Are Available for Amebiasis?
Treatment for uncomplicated cases of amebiasis generally consists
of a 10-day course of metronidazole (Flagyl) given by mouth. Your doctor may
also prescribe medication to control nausea if you need it.
If the parasite is present in your intestinal tissues, the
treatment must address not only the organism but also any damage to your
infected organs. Surgery may be necessary if the colon or peritoneal tissues have
Is the Outlook for People with Amebiasis?
Amebiasis generally responds well to treatment and should clear
up in about two weeks. If you have a more serious case where the parasite
appears in your internal tissues or organs, your outlook is still good as long
as you receive appropriate medical treatment. If amebiasis is left untreated,
however, it can be deadly.
Can I Prevent Amebiasis?
Proper sanitation is the key to avoiding amebiasis. Follow this
regimen when preparing and eating food:
- Thoroughly wash fruits and vegetables before
- Avoid eating fruits or vegetables unless you
wash and peel them yourself.
- Stick to bottled water and soft drinks.
- If you must drink water, boil it or treat it
- Avoid ice cubes or fountain drinks.
- Avoid milk, cheese, or other unpasteurized dairy
- Avoid food sold by street vendors.
As a general rule, thoroughly wash hands with soap and water
after using the bathroom and before handling food.