Giardia is a parasite. Giardiasis is the name of the illness caused by this parasite. Illness may be mild to severe. Stool can pollute streams, lakes, and ground water. This contaminated water is a common source of infection.
Some people have no symptoms.
The parasite is found in the stool of an infected person or animal. Giardiasis is treated with medicine. Some cases may require more than one course of treatment. Drink plenty of liquids to replace those lost through diarrhea. If not treated, people may have diarrhea for weeks or months.