Details

This digitally-colorized scanning electron micrograph (SEM) depicted some of the ultrastructural morphologic details of an oblong-shaped Giardia sp. protozoan cyst, revealing the filamentous nature of the cyst wall. Each cyst-wall filament is approximately 7 to 20 nanometers (nm) thick. Note that this cyst was undergoing "excystation", and was captured at a point in the process where a flagellated trophozoite was beginning to emerge from the right side of the cyst.

The protozoan Giardia causes the diarrheal disease called giardiasis. Giardia species exist as free-swimming (by means of flagella) trophozoites, and as egg-shaped cysts. It is the cystic stage, which facilitates the survival of these organisms under harsh environmental conditions. The cyst is considered the infective form, and disease is often transmitted by drinking contaminated water. As depicted in these SEMs, in the intestine, cysts are stimulated to liberate trophozoites. Cysts can be shed in fecal material, and can, thereafter, remain viable for several months in appropriate environmental conditions. Cysts can also be transferred directly from person-to-person, as a result of poor hygiene.

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CDC/ Dr. Stan Erlandsen

Dr. Stan Erlandsen

CDC - Nat. Center for Zoonotic, Vector-borne, and Enteric Disease; Giardiasis: Fact Sheet

CDC - Div. of Parasitic Diseases (DPDx); Giardiaisis

CDC Organization

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