Protozoan Parasites
Cryptosporidium parvum
The cysts of Cryptosporidium are of increasing importance because of their presence in water supplies. Passage through the stomach, or in this case chlorine bleach, weakens the wall of a cyst (left, circled). 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.
View a 590K Movie of Cryptosporidium. A longer, larger, silent version of this clip can be purchased for classroom use as part of the "Parasite Collection"available for immediate download.
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 movies, including Entamoeba killing white blood cells, on the Petri/Mann website at the University of Virginia. There are other related research links at the Entamoeba Homepage managed by Graham Clark.
Need a video of Entamoeba for classroom use? It is part of the "Parasite Collection" available for immediate download.
Giardia lamblia
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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. It is identifiable microscopically by the appearance of two "eyes" that are actually a pair of nuclei, seen in the phase contrast image (left). Giardia uses a ventral suction cup, seen in the differential interference contrast image (right), to attach to its host's intestinal epithelium. There is some evidence that a heavy infection of attached Giardia physically blocks the important transport of nutrients across the epithelium. Visit the FDA's Bad Bug Book for a further description of Giardia, including information about its transmission.
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