Amebic Dysentery


Amebiasis is a parasitic infection of the intestines caused by entamoeba histolytica. It is common in tropical areas of the world where sanitation is poor, allowing food and water supplies to be exposed to fecal contamination.

Who Is at Risk for Amebiasis?

Amebiasis is common in tropical countries with underdeveloped sanitation. It is more common in Mexico, Central American, parts of South America, South Asia, Egypt, the Middle East, and parts of Africa. It is relatively rare in the United States. Only 134 deaths from amebiasis were recorded in the U.S. from 1990 to 2007. Most cases came from California and Texas.

Persons at greatest risk for amebiasis include:

  • People who have traveled to tropical locations with poor sanitation.
  • Immigrants from tropical counties with poor sanitary conditions.
  • People who live in institutions with poor sanitary conditions.
  • Men who have sex with other men.
  • People with compromised immune systems and other health conditions.

What Causes Amebiasis?

Entamoeba histolytica is a single-celled protozoan that enters the human body primarily through ingestion of cysts in food or water. It can also enter the body via 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 fecally contaminated soil, fertilizer, or water. They can be transmitted by food handlers. Transmission can also happen during anal sex or colonic irrigation.

When cysts enter the body, they embed in the digestive tract where they release an invasive form of the parasite called the 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. Once the trophozites have breached the intestinal walls, they can enter the blood stream and travel to various internal organs. If they invade an internal organ, they can cause abscesses, infections, severe illness, and death.

The lifecycle of the ameba is completed when the host releases new cysts into the environment through infected feces.

What are the Symptoms of Amebiasis?

When symptoms occur, they tend to appear from one to four weeks after ingestion of the cysts. Only about 10 to 20 percent of people who have amebiasis become ill from it. Symptoms at this stage tend to be mild, including loose stools and stomach cramping.

If the parasite invades the lining of the 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 the bloodstream, it can end up in the 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 right upper quadrant of the torso.

How Is Amebiasis Diagnosed?

A doctor may suspect amebiasis after asking about your recent health and travel history. If amebiasis is suspected, your doctor may order a diagnostic test for entamoeba histolytica. Stool samples may also be taken over several days to screen for the presence of cysts. The doctor may order lab tests to check liver function to determine if the ameba has damaged the liver.

If damage to 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, a needle aspiration may be required to determine whether the liver is abscessed or not. An abscess in the liver is a much more serious consequence of amebiasis.

Finally, a colonoscopy may be performed to determine whether the parasite has invaded the intestinal or colon tissue.

What Treatments are Available for Amebiasis?

Treatment for uncomplicated cases of amebiasis generally consists of a ten-day course of metronidazole given by mouth. Your doctor may also prescribe medication to control nausea if you are unable to keep food or the medication down.

If the parasite has invaded the intestinal tissues or gone systemic, the treatment must address not only the organism, but any damage done to the infected organs. If the infection has caused perforations in the colon or peritoneal tissues, surgery may be required.

What Is the Outlook for People with Amebiasis?

Amebiasis generally responds well to treatments and should clear up in about two weeks. If the ameba has penetrated the internal tissues and organs, survival is still good as long as appropriate medical treatment is received. Left untreated, however, it can be deadly. About 70,000 people around the world die of amebiasis each year.

How Can I Prevent Amebiasis?

Proper sanitation is the key to avoiding amebiasis:

  • Thoroughly wash hands with soap and water after using the bathroom and before handling food.
  • Thoroughly wash fruits and vegetables before eating.
  • 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 with iodine.
  • Avoid ice cubes or fountain drinks.
  • Avoid milk, cheese, or other unpasteurized dairy products.
  • Avoid food sold by street vendors.