What Is It?

Gastrointestinal amebiasis is an infection of the large intestine caused by microscopic one-celled parasites commonly known as amoebas. Their scientific name is Entamoeba histolytica. Because these parasites live in the large intestine, they are carried in the feces of infected persons, and they can contaminate drinking-water supplies in places where sanitation is poor. They also can contaminate fruits and vegetables grown in areas where human feces are used as fertilizer, or can be transferred on the dirty hands of infected people who have poor hygiene.

Once amoebas enter the mouth, they travel through the digestive system and settle in the large intestine. The harmless strains of the parasite (Entamoeba dispar) live there without causing damage. E. histolytica also can live in the intestine without causing symptoms, but this parasite can cause severe disease. These amoebas may invade the wall of the intestine, causing amoebic dysentery, an illness characterized by intestinal ulcers, bleeding, increased mucus production and diarrhea. These amoebas also may pass into the bloodstream and travel to the liver or, infrequently, the brain, where they form abscesses (pockets of infection).

About 10 percent of the world’s population is infected with amoebas, particularly people who live in Mexico, India, Central America, South America, Africa and the tropical portions of Asia. In industrialized countries, amebiasis is most common in recent immigrants and travelers who visit countries where amoebas are prevalent. Cases also have been reported in homosexual men, prisoners and residents of other institutions.

In more than 90 percent of cases, the infecting strain of amoeba does not cause any symptoms. When symptoms occur, they usually begin within months after amoebas first enter the body. In some people, symptoms are mild, consisting of mild pain and gurgling sounds in the lower abdomen, with two or three loose stools daily. In other people, however, there can be full-blown symptoms of amoebic dysentery, including high fever, severe abdominal pain and 10 or more episodes of diarrhea daily. Typically, this diarrhea is watery or contains blood and mucus.

When amoebas spread to the liver and cause liver abscess, symptoms can include fever, nausea, vomiting, pain in the upper right portion of the abdomen, weight loss and an Enlarged liver. It is possible for a person to develop symptoms of an amoebic liver abscess without ever having had the diarrhea associated with amoebic infection of the intestines.

Diagnosis

Your doctor will ask you about your history of exposure to amoebas, especially about any recent trips to areas where amoebas are common. Your doctor also will look for specific symptoms of amoebic infection, especially frequent Diarrhea or loose stools and the presence of blood and mucus in your bowel movements. Since other conditions can cause bloody diarrhea and there are other types of infectious diarrhea, information about bowel disease in the family and travel are particularly important.

Usually a series of three fresh stool samples will be checked in the laboratory for the presence of E. histolytica. In many cases, this stool test is all that is needed to confirm the diagnosis. Several different blood tests that can make a diagnosis with a high degree of accuracy also are available. In special cases, when the diagnosis is not clear after stool and blood tests, a test called a proctosigmoidoscopy or colonoscopy may be needed to allow your doctor to examine the intestinal wall directly and to take tissue samples for laboratory examination. In these tests, the rectum and colon are examined with a thin, lighted instrument.

When symptoms of fever and abdominal pain, especially on the right upper side, suggest a possible liver abscess, an Ultrasound or CT scan of the liver may be done. Since patients who only have a liver abscess may no longer have parasites in the intestines, stool tests may be less helpful. In these situations, the diagnosis is confirmed either by a blood test or examination of the abscess by a needle aspiration or biopsy. In a needle aspiration or biopsy, a small piece of tissue from the abscess is removed and examined in a laboratory.

Expected Duration

Harmless amoebas can live in the intestines for years without causing symptoms. When invasive amoebas cause symptoms of amoebic dysentery, attacks can last from a few days to several weeks. Unless you are treated, you can have another attack.

There is no immunization to protect against gastrointestinal amebiasis. If you are traveling to areas where amebiasis is common, you can decrease your risk of infection by drinking only canned or bottled sodas or water that has been boiled or bottled. Eat only foods that have been cooked thoroughly, and drink only pasteurized milk and dairy products. If you eat raw fruit, eat only fruits that you have freshly peeled.

Gastrointestinal amebiasis is treated with nitroimidazole drugs, which kill amoebas in the blood, in the wall of the intestine and in liver abscesses. These drugs include metronidazole (Flagyl) and tinidazole (not available in the United States). Metronidazole usually is given for 10 days, either orally (by mouth) or intravenously (directly into the veins). To kill amoebas and cysts confined to the intestine, three drugs, called luminal drugs, are also available: iodoquinol (Diquinol, Yodoquinol, Yodoxin), paromomycin (Humatin) and diloxanide furoate (Furamide). One of these drugs is used in patients along with metronidazole when active gastrointestinal symptoms are present. In people who pass amoebas in their stools without having symptoms of amebiasis, the luminal drugs alone can clear the cysts from the bowel.

Call your doctor whenever you have continuing diarrhea, especially when Diarrhea contains blood and mucus. If you have severe Abdominal pain, especially in the right upper side, and a fever, you should visit a doctor the same day. When you have nonbloody diarrhea that is frequent, and you have symptoms of dehydration such as dizziness, you also should call your doctor.

Drug treatment can cure amebiasis within a few weeks. However, because medication does not prevent reinfection, repeat episodes of amebiasis may occur if the patient continues to live in, or travel to, areas where amoebas are found. Among children in developing countries, especially infants and those younger than 5, gastrointestinal amebiasis can be fatal. Worldwide, amebiasis is the third most common cause of death from parasitic infections.

Last Edited: 15 Aug. 2005