What is amebiasis?

Causes and Symptoms

Amebiasis entails infection of the colon by the single-cell parasite
Entamoeba histolytica. The majority of people infected—about 80 to 90 percent—do not develop symptoms and may be chronic carriers, a fact that is difficult to detect. Most of those who are symptomatic experience loose stools, intermittent diarrhea, intensified flatulence, and stomach cramps. Severe cases involve bloody diarrhea (dysentery), abdominal tenderness, mucus in the stool, or fever.

The parasite spreads when a person swallows food or water containing infected feces. Infection occurs in two forms, the active parasite (trophozoite) or dormant parasite (cyst form, which may activate in the intestinal tract). The trophozoites attack the lining of the colon, feeding on bacteria and tissue, and may cause ulcers. Sometimes a lump (ameboma) forms that is large enough to obstruct the intestines.

Occasionally, the trophozoites penetrate the bowel wall and enter the abdominal cavity, causing peritonitis, or they may travel to other organs. The liver may be infected, with the parasite forming an abscess that can cause fever, chills, and weight loss. Much more rarely, the lungs, brain, or skin on the buttocks becomes infected.

Treatment and Therapy

Physicians test for amebiasis by examining three to six stool samples for evidence of the parasite. A colonoscopy may be used to locate ulcers and take a tissue sample. Abscesses in the liver can be located by ultrasound or computed tomography (CT) scan but cannot directly confirm the presence of Entamoeba histolytica.

The standard treatment is to give the patient antibacterial drugs. For those who are not sick, one antibiotic is given; for those with symptoms, there are usually two. The most common combination is metronidazole and iodoquinol, administered orally for ten days. Paromomycin and diloxanide furoate are also used, and for liver abscess, tinidazole. Follow-up tests of stool samples after two to four weeks are used to check for the presence of the parasite, as relapses may occur. Antidiarrheal medications may be needed to help patients control their bowels.

Perspective and Prospects

The vast majority of amebiasis infections occur in countries with poor sanitation or that use human waste as a crop fertilizer. Therefore, amebiasis is a form of travelers’ diarrhea for tourists in Mexico, Central America, parts of South America and Africa, and South Asia. Sexual transmission is possible. Mass outbreaks are rare, but one arose during the 1933 Chicago World’s Fair when contaminated water led to about one thousand symptomatic cases and fifty-eight deaths.

Bibliography:

"Amebiasis." MedlinePlus, Mar. 22, 2013.

Beers, Mark H. The Merck Manual of Medical Information. New York: Pocket Books, 2003.

Ericsson, Charles. Travelers’ Diarrhea. 2nd ed. Hamilton, Ont.: B. C. Decker, 2008.

McCoy, Krisha, and Michael Woods. "Amoebic Dysentery." Health Library, Nov. 26, 2012.

"Parasites - Amebiasis." Centers for Disease Control and Prevention, Nov. 2, 2010.

Parker, James N. The Official Patient’s Sourcebook on Travelers’ Diarrhea. Urbana, Ohio: Icon Health, 2002.

Schwartz, Eli. Tropical Diseases in Travelers. Hoboken, N.J.: Blackwell, 2009.