binary fission definition understanding biology

The majority of amebiasis cases occur in developing countries. Pathogenic Entamoeba species occur worldwide and are frequently recovered from fresh water contaminated with human feces. Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment. Cysts can survive days to weeks in the external environment and remain infectious in the environment due to the protection conferred by their walls. Trophozoites multiply by binary fission and produce cysts, and both stages are passed in the feces.

Trophozoites may remain confined to the intestinal lumen (A: noninvasive infection) with individuals continuing to pass cysts in their stool (asymptomatic carriers). Trophozoites can invade the intestinal mucosa (B: intestinal disease), or blood vessels, reaching extraintestinal sites such as the liver, brain, and lungs (C: extraintestinal disease). Excystation occurs in the small intestine and trophozoites are released, which migrate to the large intestine. Infection with Entamoeba histolytica (and E.dispar) occurs via ingestion of mature cysts from fecally contaminated food, water, or hands. Exposure to infectious cysts and trophozoites in fecal matter during sexual contact may also occur. Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool. Cysts and trophozoites are passed in feces.

Binary fission definition understanding biology