Amebiasis Life Cycle
Amebiasis is an infection caused by protozoa of the genus Entamoeba. Entamoeba histolytica is the most common pathogen. Amebiasis involves the large intestine but also can affect the liver and other organs.
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Initial Infection
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Infection occurs when you ingest mature Entamoeba cysts. This happens when you--the host--consume food, water or other items that are contaminated with fecal material. Infection also can occur through exposure to feces during sexual activity.
The Trophozoite Stage
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The cysts eventually make their way to the small intestine, where they release trophozoites. The trophozoites migrate to the large intestine, where they multiply by binary fission, meaning division into two identical copies. In some hosts, trophozoites will invade the mucosa of the intestines, travel through the bloodstream and infect other organs such as the liver, brain and lungs.
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The Cyst Stage
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Within the large intestine, the trophozoites also produce more cysts. Trophozoites and cysts are then passed along with the stool. The trophozoites cannot exist outside of the body and die. The cysts, however, can survive for days or even weeks outside the human host.
Symptoms
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Symptoms of amebiasis include diarrhea, abdominal pain, cramping, fever and pain in the region of the liver. Some people with the parasite have no symptoms. The disease occurs worldwide and is common in Africa, India and Latin America. Poor sanitation is a common cause of amebiasis.
Diagnosis and Treatment
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Diagnosis can be made by examining a recently collected stool sample for the parasite. The drugs of choice for asymptomatic infections are areiodoquinol, paromomycin and diloxanide furoate. The drugs of choice for symptomatic intestinal disease and extraintestinal infections include metronidazole and tinidazole followed by treatment with iodoquinol, paromomycin or diloxanide furoate.
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