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Giardia is a parasite that infects the intestines of humans and animals. When a person gets sick, the infection is called giardiasis, or ‘beaver fever’. Symptoms of giardiasis include diarrhea, stomach cramps, gas, bloating, nausea, and fatigue. For more information about giardiasis, see HealthLinkBC File # 10 Giardia Infection, or visit BC Centre for Disease Control - Giardiasis.

Conditions Basics

What is giardiasis?

Giardiasis (say "jee-ar-DYE-uh-sus") is an infection of the intestines caused by the parasite Giardia lamblia. The illness is also called giardia (say "jee-AR-dee-uh"). It can happen if you drink water that has been contaminated.

How is it spread?

You may become infected with giardia if you eat food or drink water that is tainted with infected human or animal waste.

In Canada and the United States, you can get giardia by drinking untreated water from wells, streams, rivers, and lakes. This is true even in mountain lakes and streams where the water may seem very pure.

You can also get the infection if you swallow contaminated water while you swim.

You can get giardia from someone else through:

  • Close contact with someone who is infected.
  • Working in daycare centres for young children. For example, if you change a diaper and don't wash your hands afterward, anything or anyone you touch could get infected. You could even get the illness yourself if you touch your mouth or eat food that you've touched. Children in daycare centres are also more likely to get infected.
  • Working or living in nursing homes or other care centres where people may have poor bowel control and poor hygiene.
  • Some types of sexual contact, such as anal-oral contact.

After a person is exposed to the parasite, it usually takes 7 to 14 days for the infection to develop. You can pass the infection to others during the entire time you are infected. You may be infected for months, even if you don't have symptoms.

What are the symptoms?

Giardiasis can cause diarrhea, stomach cramps, gas, and nausea. You may feel sick once and then get better. Or your symptoms may come and go for some time. Some children with giardiasis don't grow or gain weight normally. Sometimes giardiasis doesn't cause any symptoms.

How is it diagnosed?

To diagnose giardiasis, your doctor will test your stool for the parasite that causes the infection. Your doctor will also ask questions about your past health and do a physical examination.

In some cases, you may be tested for giardiasis even though you don't have any symptoms. For example, this could happen during an outbreak at a daycare centre.

How is giardiasis treated?

If you have symptoms, your doctor may prescribe medicine to kill the parasite. It's important to take the medicine for as long as prescribed, so the infection doesn't return.

You can manage your symptoms at home.

  • If you have diarrhea, try eating small amounts of food when you feel like eating.
  • Take frequent sips of clear fluids like rehydration drinks to avoid dehydration. This is especially important for children. They can get dehydrated quickly.

Talk to your doctor if you are having problems with milk and milk products. Some people with giardia have trouble digesting milk products.

If you don't have symptoms, there is usually no treatment. But your doctor may give you medicine to lower the chance that you will pass the infection to others.

How can you prevent it?

There are some things you can do to avoid giardiasis.

  • Don't drink untreated or unpurified water. If you are camping or hiking, boil or purify water from lakes and streams before you drink it.
  • When you travel in high-risk areas, drink bottled water and avoid raw fruits and vegetables. Don't drink beverages containing ice cubes made from untreated water.
  • Wash your hands often to prevent getting giardiasis from an infected person. This is very important before you prepare food, after you change diapers, use the toilet, or help someone else use the toilet.


Current as of: October 31, 2022

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
W. David Colby IV MSc, MD, FRCPC - Infectious Disease