Protozoal Diseases of the Digestive System Amoebic dysentery. Amoebic dysentery is caused by the amoeba Entamoeba histolytica. This protozoan exists in nature in the cyst form and is transmitted by contaminated food and water. In patients, the amoebas revert to trophozoites (feeding forms) and invade the intestinal lining. Then they enter the bloodstream and move to distant organs, such as the liver and lung. Infected individuals pass the cysts in stools and remain carriers for long periods. A drug called metronidazole is used for therapy. Giardiasis. Giardiasis is a protozoal disease caused by the flagellate Giardia lamblia. The organism is taken into the body in its cyst form in contaminated food and water. In the intestine, the trophozoites emerge from the cysts and multiply along the walls of the intestine. A foul-smelling, watery discharge accompanies the infection, followed by abdominal pain and diarrhea. Hikers,
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