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 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:

Risk Factors

Giardiasis is more common in young children and older adults. Other factors that increase your chance of giardiasis include:


Symptoms usually start 5 to 28 days after infection. Not all people who are infected have symptoms. However, all people who are infected can transmit the disease.
Symptoms may include:


The doctor will ask about your symptoms and medical history. A physical exam will be done.
Your bodily fluids, tissue, and waste products may be tested. This can be done with:
If you are diagnosed with giardiasis, everyone living in your household should be tested for the infection as well.


Giardiasis is treated with a prescription antiparasitic drug. The medication is usually given for 5-10 days.
This condition may be resistant to medications. This may make treatment difficult. It may also mean that you may be sick longer.


To reduce your chances of getting or spreading giardiasis to others:


Family Doctor—American Academy of Family Physicians

National Institute of Allergy and Infectious Diseases


Canadian Association of Gastroenterology

Public Health Agency of Canada


Adam RD. Biology of Giardia lamblia. Clin Microbiol Rev. 2001;14(3):447-475.

Giardiasis. Nemours Kids Health website. Available at: Updated September 2011. Accessed August 14, 2013.

Parasites–giardia. Centers for Disease Control and Prevention website. Available at: Updated March 8, 2011. Accessed August 14, 2013.

Nash TE. Surface antigenic variation in Giardia lamblia. Mol Microbiol. 2002;45(3):585-590.

Revision Information