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 specific, 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

Risk Factors

Giardiasis is more common in young children and older adults. Other factors that increase your chance of giardiasis include:
  • Unsanitary or crowded living conditions
  • Drinking untreated water, such as:
    • Well water
    • Stream or lake water
  • Low stomach acid, often found in:
    • Older adults
    • People on ulcer drugs
  • Oral-anal sex
  • A weakened immune system
  • Working or staying in a daycare center or nursing home
  • International travelers
  • Internationally adopted children, who may have more than one parasitic infection
  • Hikers, campers, and swimmers

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