Giardiasis is a gastrointestinal infection. It is one of the most common parasitic diseases in the world.

Gastrointestinal System
The Intestines
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Giardiasis is caused by a tiny parasite. Giardia cysts are a resistant form of the parasite that can survive outside a human or animal body. These cysts cause the spread of this disease. For infection to occur, a person must ingest Giardia cysts by mouth. After cysts are ingested, the parasites start growing and multiplying in the small intestine. Ingesting as few as ten parasitic cysts can cause an infection.

Giardiasis can occur by:

  • Contact with feces containing the parasitic cysts. Infected feces can be:
    • Human
    • Animal such as cats, dogs, beavers, and cows
  • Eating food, drinking water, or swimming in water contaminated by the parasitic cysts
  • Contact with a person's hands that are contaminated with parasite cyst-infected stool