Giardia
Any warm-blooded animal can serve as a source of infection for Giardia lamblia by contaminating water sources with infected feces. Beavers in particular are significant sources of human Giardiasis. Once a cyst has found a new host it will begin the transformation into a mobile trophozoite. Trophozoites attach to the surface of the small intestine inhibiting the intake of nutrients. When forces to leave the organism, the trophozoite will once again resume the infective cyst form. The cyst can be confirmed using an immunofluorescent technique to identify the following organelles: four nuclei, two pairs of median bodies and a pair of axonemes. The United States Environmental Protection Agency Method 1623 (used for detection of Giardia and Cryptosporidium) describes the organelles accordingly:
- Axoneme - an internal flagellar structure that occurs in some protozoa, such as Giardia, Spironucleous, and Trichonmonas.
- Median bodies - Prominent, dark-staining, paired organelles consisting of microtubules and found in the posterior half of Giardia. In G. intestinalis (from humans), these structures often have a claw- hammer shape, while in G. muris (from mice), the median bodes are round.
- Nucleus - A membrane-bound organelle containing genetic material. Nuclei are a prominent internal structure seen both in Cryptosporidium oocysts and Giardia cysts. In Cryptosporidium oocysts, there is one nucleus per sporozoite. One to four nuclei can be seen in Giardia cysts.
Above:
Immunofluorescence image of several Giardia lamblia cysts. Cysts should
have an intense apple green fluorescence on the periphery of their cyst wall, and
measure 11-14 microns in length. Scale bar is 10 microns.
Photo Credit: H.D.A. Lindquist, U.S. EPA
Giardia cysts are 8-18 µm long are 5-15µm wide and can survive outside a host while waterborne for several days before dying.
For more interesting information regarding Giardia, click on the hyperlink to visit the USEPA (United States Environmental Protection Agency) USEPA Microbiology Homepage.
You can also learn more about Giardia by visiting the American Water Works Association website and read the fact sheet that they have compiled.
Please feel free to send any water quality comments or questions that you may have to waterquality@tmwa.net.
