Giardia... Waterborne Parasite Giardia is a parasite that infects warm-blooded animals and humans causing giardiasis, an intestinal illness which can cause nausea, anorexia, fever, and severe diarrhea. The symptoms last for several days, and the body can naturally rid itself of the parasite in one to two months. However, for people with weakened immune systems, the body often cannot rid itself of the parasite without medical treatment. Giardia can survive for long periods of time because it has an outer shell, called a cyst, that enables it to live outside an animal's body. Water supplies can become contaminated either by the activity of animals or by the introduction of sewage into the water supply. Wild and domestic animals have been shown to be major contributors in contaminating water supplies. Treating the water supply can control giardia. Chlorine and ozone are two disinfectants known to kill giardia cysts. Filtering the parasite from the water is also effective. The most effective water treatment, however, is the combination of using both a disinfectant and filtering. Giardia is the most commonly identified pathogen in waterborne disease outbreaks.

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