What is Giardiasis?

Giardiasis (gee-are-dye-uh-sis) is a diarrheal disease caused by microscopic parasites called Giardia. These parasites can live in the intestines of many mammals, including humans. Although many species of Giardiaare found worldwide, only Giardia lamblia (known also as G. intestinalis, G. duodenalis) causes infection in humans.

Giardiasis is a common cause of waterborne disease in humans. Giardiasis is sometimes called “beaver fever” after an outbreak in which hikers at Banff National Park became ill from drinking stream water contaminated with Giardia from beavers.


What are the symptoms of Giardiasis?

Giardia infection may cause a variety of intestinal symptoms, including:

  • diarrhea
  • bloating, gas or flatulence
  • greasy stools that tend to float
  • stomach or abdominal cramps
  • upset stomach or nausea
  • fatigue
  • weight loss

Symptoms of giardiasis usually begin 7 to 10 days after exposure, but it can also be as little as 3 days or as long as 25 days. The symptoms typically last two to six weeks, but may occasionally last longer.

Prolonged infection with Giardia can lead to complications, such as arthritis or damage to the cells which line the intestines.  Persons infected with Giardia may not have any symptoms. These asymptomatic individuals can still pass the disease on to others.  If you have any signs and symptoms of illness, and you have exposure to possible sources of Giardia parasite, contact your physician.



How is Giardiasis spread?

Giardia forms spore-or egg-like cells called cysts, which can survive outside the body for long periods of time. The cysts are in a resting or dormant stage that helps the organism survive in unfavourable environmental conditions.

These cysts are released with the bowel movements of infected humans or animals.  Giardiasis is spread when people accidentally ingest the parasite or its cyst. It takes only 1 to 10 cysts to cause infection. Approximately one million cysts could fit under a fingernail.



You can become infected by:

  • ingesting contaminated drinking or recreational water
  • touching your mouth with contaminated hands
  • putting something in your mouth that has come into contact with the droppings of infected animals or the stool of infected humans
  • eating raw or undercooked food that is contaminated
  • inadequately washing hands before preparing food, before eating, and after toileting or diapering



How is Giardiasis diagnosed and treated?

  • Giardiasis is usually diagnosed by examination of stool samples. Patients may be asked to submit multiple stool samples because detection of Giardia can be difficult.
  • Several anti-parasitic medications are available to treat giardiasis. Your health care practitioner will decide if and what medication is needed for you.  Persons with diarrhea should generally drink lots of liquids to avoid dehydration.
  • If you think you have giardiasis you should see your doctor for testing, advice and treatment.


How can you prevent Giardiasis?

  • Wash your hands with soap and water for at least 15 seconds:
    • after using the toilet
    • after changing diapers
    • after assisting others with the toilet
    • after contact with animals
    • after working in the garden, and
    • before and after handling food
  • Avoid swallowing water while swimming in lakes, rivers or pools.
  • Avoid drinking water from shallow wells, rivers, lakes or streams. Only drink water that you know is uncontaminated. If you are not sure, treat the water yourself, for example, by boiling for at least five minutes.
  • Peel raw vegetables and fruits before eating. Use uncontaminated water to wash fruits and vegetables.
  • Giardiasis has been associated with camping and travelling. Campers and travellers should be aware if giardiasis is common in the area they will be visiting.



What causes Giardiasis outbreaks?

Poor hand hygiene practices have been associated with outbreaks of giardiasis in daycare centres and institutions. Giardiasis outbreaks have also been associated with consumption of contaminated drinking and recreational water.


This page provides basic information only. It must not take the place of medical advice, diagnosis or treatment. Always talk to a health care professional about any health concerns.

Source:  Ontario Ministry of Health and Long-Term Care, Public Health Division.


For Further Information

Call the Infectious Disease Program: (807) 625-5900

or toll-free 1-888-294-6630

Health Topic
Diseases & Infections