When in the gut, four spindle-shaped motile sporozooites burst from the cyst to infect gut epithelial cells and continue their life cycle. A diagram of the life cycle, plus information on prevalence and current research on this organism is available in Steve Upton's Parasitology page at Kansas State University. Entamoeba histolytica Entamoeba histolytica , another water-borne pathogen, can cause diarrhea or a more serious invasive liver abscess. When in contact with human cells, these amebae are cytotoxic. There is a rapid influx of calcium into the contacted cell, it quickly stops all membrane movement save for some surface blebbing.
Internal organization is disrupted, organelles lyse, and the cell dies.
The ameba may eat the dead cell or just absorb nutrients released from the cell. There are other related research links at the Entamoeba Homepage managed by Graham Clark. Giardia lamblia Signs posted in wilderness areas often warn about Giardia in streams. Commonly found in wild animals such as the beaver, this graceful, flagellated organism may infect unwary hikers. But giardiasis can also be contracted via contaminated foods.