Giardiasis is a gastrointestinal infection. It is one of the most common parasitic diseases in the world. It may be responsible for for up to a billion cases annually worldwide.
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. Once 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 be contracted by:
Contact with feces containing the parasitic cysts. Infected feces can be:
- Animal (less often), including beavers, cats, dogs, 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
A risk factor is something that increases your chance of getting a disease or condition.
- Age group: young children and elderly adults
- Unsanitary or crowded living conditions
Drinking untreated water, such as:
- Well water
- Stream or lake water
Low stomach acid, often found in:
- Elderly people
- People on ulcer drugs
- Oral-anal sex
- An impaired immune system
- Working or staying in a daycare center or nursing home
- International travelers
- Internationally adopted children, who may harbor 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
- Nausea or vomiting
- Weight loss
- Mild fever (rare)
The doctor will ask about your symptoms and medical history, and perform a physical exam. Tests may include:
- Laboratory exam of several (usually three) stool samples
- Stool testing for Giardia proteins (called the Giardia antigen test)
- In some cases, testing of a fluid or tissue sample from the intestine
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 and may be one of the following:
This condition may be resistant to any of these medications or to several others occasionally used. Resistance may complicate treatment and prolong illness.
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
- Bring bottled water for drinking, cooking, and brushing teeth.
- Purify untreated water before using—boil, filter, or otherwise 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 adequately cooked and served steaming hot.
- Do not let children with diarrhea go into swimming pools.
- Keep swimming pools adequately chlorinated.
- Stay home from work and keep children home from school or daycare until the infection is gone.
The American Academy of Family Physicians
Maryland Department of Health and Mental Hygiene
Massachusetts Department of Public Health
The Canadian Association of Gastroenterology (CAG)
Public Health Agency of Canada
Adam RD. Biology of Giardia lamblia . Clin Microbiol Rev. 2001;14:447
American Academy of Family Physicians website. Available at: http://www.familydoctor.org .
Harrison's Principles of Internal Medicine . 15th ed. McGraw-Hill Professional Publishing; 2001.
Massachusetts Department of Public Health. Bureau of Communicable Disease Control website. Available at: http://www.state.ma.us/dph/cdc .
The Merck Manual of Medical Information . Simon and Schuster, Inc; 2000.
Nash TE. Surface antigenic variation in Giardia lamblia . Mol Microbiol. 2002;45:585.
Last reviewed November 2008 by
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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