• Giardiasis


    Giardiasis is a gastrointestinal infection. It is one of the most common parasitic diseases in the world.
    Gastrointestinal System
    The Intestines
    Copyright © Nucleus Medical Media, Inc.


    Giardiasis is caused by a tiny parasite called Giardia lamblia . 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 (less often), 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

    Factors that increase your risk of getting this disease include:
    • Age group: young children and older adults
    • 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


    Symptoms usually start 5 to 28 days after infection. Not all people who are infected have symptoms. But, all people who are infected can transmit the disease.
    Symptoms may include:
    • Diarrhea , acute or chronic
    • Loose, greasy, foul-smelling stools
    • Abdominal pain or cramps
    • Bloating
    • Gas
    • Nausea or vomiting
    • Weight loss
    • Mild fever (rare)


    The doctor will ask about your symptoms and medical history. A physical exam will be done.
    Your doctor may want to lab results from your bodily fluids, waste products, or tissue. This can be done with:
    • Stool tests
    • Fluid or tissue samples taken from the intestine for testing
    If you are diagnosed with giardiasis, everyone living in your household should be tested for infection as well.


    Giardiasis is treated with a prescription antiparasitic drug. The medication is usually given for 5 to 10 days. Some of these medications include:
    • Metronidazole
    • Furazolidone
    • Paromomycin
    • Nitazoxanide
    • Tinidazole
    This condition may be resistant to any of these medications or to several others that are sometimes used. This may make treatment difficult. It may also mean that you may be sick longer.


    Follow these guidelines to prevent getting or spreading giardiasis:
    • Maintain good personal hygiene.
    • Wash hands several times a day, especially:
      • Before eating or preparing food
      • After a bowel movement
      • After changing a diaper
      When camping:
      • Bring bottled water for drinking, cooking, and brushing teeth.
      • Purify untreated water before using—boil, filter, or sterilize.
    • Thoroughly wash or peel raw fruits and vegetables before eating.
    • When traveling overseas:
      • Use only bottled water for drinking, cooking, or brushing teeth.
      • Only eat food that is well cooked and served steaming hot.
    • Do not let children with diarrhea go into swimming pools.
    • Keep swimming pools properly chlorinated.
    • Stay home from work. Keep children home from school or daycare until the infection is gone.


    American Academy of Family Physicians http://www.familydoctor.org

    National Institute of Allergy and Infectious Diseases http://www.niaid.nih.gov


    The Canadian Association of Gastroenterology (CAG) http://www.cag-acg.org/

    Public Health Agency of Canada http://www.phac-aspc.gc.ca


    Adam RD. Biology of Giardia lamblia . Clin Microbiol Rev. 2001;14:447

    Giardiasis. KidsHealth.org website. Available at: http://kidshealth.org/parent/infections/stomach/giardiasis.html . Updated September 2011. Accessed January 8, 2013.

    Parasites–giardia. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/parasites/giardia/ . Updated March 8, 2011. Accessed January 8, 2013.

    Nash TE. Surface antigenic variation in Giardia lamblia . Mol Microbiol. 2002;45:585.

    Revision Information

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