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Giardia spp. Information

Giardia lamblia is a pathogenic protozoan with a size range of 8-18 um long and 5-15 um wide that reproduces in the intestinal tract of mammals. In the final stage of its life cycle, Giardia asexually produces environmentally resistant structures known as cysts, and these are shed within animal feces and can contaminant food and water sources. In humans, infection may result in acute gastrointestinal distresses including diarrhea, weight loss, vomiting, or fatigue; however, certain individuals may not manifest symptoms but otherwise remain infected. These asymptomatic carriers can for many years potentially transmit infection to others. Many mammalian reservoir hosts, including dogs, cats, beavers and muskrats, can carry the parasite. These hosts readily shed cysts within their feces which may contaminate the watershed. Giardia is common in surface waters and generally, for potable water, cysts are removed by filtration and/or inactivated by chlorine disinfection. However, if filtration is deficient or water is not properly treated, cysts can be present in finished drinking water and may be ingested by humans causing gastroenteritis of varying severity. Several waterborne outbreaks have been attributed to Giardia.

Detection of cysts in water samples is accomplished by reacting immunofluorescent antibodies with specific biochemical markers on the surface of the cysts. Cysts successfully labeled with these fluorescent tags can then be visualized using IFA microscopy. After detecting a putative cyst with immunofluorescent antibodies, DAPI (a nuclear stain) and DIC microscopy features aid in the confirmation/invalidation process.



AWWA (American Water Works Association). Waterborne Pathogens. Manual of Water Supply Practices, M48, First Edition. 1999. Denver.

Betts W.B., D. Casemore, C. Fricker, H. Smith, and J. Watkins, ed. Protozoan Parasites and Water. 1995. The Royal Society of Chemistry. Cambridge.


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Last modified: June 11, 2007