Division of Parasitic Diseases - Giardiasis Fact SheetWhat is giardiasis?
Giardiasis (GEE-are-DYE-uh-sis) is a diarrheal illness caused by a one-celled, microscopic parasite, Giardia intestinalis (also known as Giardia lamblia). Once an animal or person has been infected with Giardia intestinalis, the parasite lives in the intestine and is passed in the stool. Because the parasite is protected by an outer shell, it can survive outside the body and in the environment for long periods of time.
During the past 2 decades, Giardia infection has become recognized as one of the most common causes of waterborne disease (found in both drinking and recreational water) in humans in the United States . Giardia are found worldwide and within every region of the United States.