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Giardiasis is a fairly common disease in Canada and around the world. The parasite that causes it,Giardia lamblia, is one of the most commonly isolated enteric parasites in Canada. In developing countries, it can be found in up to 30% of the population. Antony van Leeuwenhoek, the inventor of the microscope, is credited with first discovering it in the 1600's. 

It is often water-borne, or spread in institutions where hygiene is poor. It is also called beaver fever, because the parasite has been discovered in beavers, but many wild and domestic animals carry this organism in their gut.

Although generally not a serious illness, it can have some long lasting side effects if left untreated - an issue primarily for people whose immune systems are weakened. It is easily prevented by good hygiene and safe food handling practices. It requires a higher degree of drinking water treatment, however, for operators of water systems supplied by surface water.

Information for Health Professionals

Giardiasis is an infection of the intestinal tract. When a person gets sick from this infection it is called giardiasis. It is caused by one-celled parasites (protozoa); they belong to the genus Giardia, and the particular parasite causing most of these infections is called Giardia lamblia (and less commonly G. intestinalis and G. duodenalis).

Giardiasis is a fairly common protozoan diarrhea in B.C. and the world. It is common in the rural and wilderness areas of Western Canada, mostly spread through contaminated drinking water. Over the past 10 years (1999 to 2008), an average of 770 infections per year have been reported to the B.C. Centre for Disease Control. The number of infections has steadily declined since at least 1998.


Giardia may cause: 

  • diarrhea
  • abdominal cramps
  • gas
  • bloating
  • frequent loose and pale greasy stools
  • nausea
  • poor absorption of fats and vitamins
  • weight loss, and
  • fatigue.

Symptoms start an average of seven to ten days (range: three to 25 days or longer) after exposure to the parasite and may last for months. Often a person can be infected and have no symptoms. In some cases, symptoms can return after you have started to get better.

People with HIV/AIDS may experience longer and more serious symptoms from a giardia infection.



Giardia are spread by the fecal-oral route. Fecal material from infected humans or animals can get into our mouths by:

  • consuming contaminated food or drink
  • contact with the feces of infected humans that is not followed by proper hand washing
  • contact with the feces of domestic or wild animals, including pets and farm animals, that is not followed by proper hand washing. Pets may also have fecal matter on their hair or fur that is transferred to our hands when we touch them

Giardiasis is commonly a water-borne disease. Giardia cysts (the dormant form of giardia) are very hardy organisms that survive for long periods of time in the environment including cold water. 

You can ingest giardia by: 

  • Drinking inadequately treated water contaminated by humans or animals leaving their droppings in or near water sources such as streams, rivers, lakes or shallow wells
  • Ingesting contaminated water while swimming in lakes, ponds, streams, rivers, swimming pools and hot tubs
  • Eating contaminated food
  • Contact with the feces of an infected person (e.g. after diaper changing, or during sexual contact)

The spread of giardiasis in institutions such as day cares is a significant cause of outbreaks, and is due to poor hygiene. Water-borne spread is important in localized outbreaks, and is more significant than the spread of infection through food.


Prolonged and/or severe infection can result in reactive arthritis and damage to the cells lining the intestinal tract. People who have weakened immune systems are more prone to lengthy infections and should consult a health practitioner as soon as they suspect an infection.


Microscopic examination of one or more stool samples is the means to a diagnosis of giardiasis.


People with health immune systems normally clear the infection in about a month. However, giardiasis responds fairly well to anti-parasitic medication. Your doctor will decide if treatment with anti-parasitic medication is necessary in your case.

After your infection, you may have difficulty digesting milk and milk products. This causes symptoms similar to those of a giardia infection and can last several weeks. Avoid milk and milk products for a few weeks and then slowly add them back into your diet. Consult your doctor if you have questions.


If you think you have a giardia infection, see your family doctor for testing, advice and treatment. 

Giardia is passed in the feces; therefore, people with diarrhea which may be due to infection should not go to work or school. Giardiasis spreads easily in day care settings. If you are a food handler or health care worker it is possible for you to transmit giardia to others while carrying out your duties in these settings. 

Do not work while you have diarrhea or vomiting and do not return to work until 48 hours after your last loose stool or episode of vomiting. This time period will ensure you have a chance to recover and lessen the possibility of transmitting the infection to others.

Children in day care who have diarrhea can be cared for temporarily in an area separate from other children until picked up by their parents. Children cannot return to day care until 48 hours after their last loose stool or episode of vomiting. To ensure proper hand washing, children in day cares should be supervised by an adult when washing their hands. 

 If you recover without treatment, you may excrete giardia in your stools for several months and possibly infect others. After using the toilet and before eating or preparing foods wash your hands thoroughly with liquid soap and water.


  1. If your local drinking water provider has issued a Boil Water Notice for your community water system, take the advice seriously.
  2. Do not drink untreated surface water from springs, streams, rivers, lakes, ponds or shallow wells. Assume it is contaminated with animal feces. Boil or filter water from these sources that is used for:
  3. drinking
  4. making ice cubes
  5. washing uncooked fruits and vegetables
  6. making baby formula
  7. brushing teeth
  8. rinsing dentures
  9. and any purpose where water will be consumed without proper heat treatment.

See below for directions.

  • When camping, do not relieve yourself within 100 feet of a water source.
  • If you have a giardia infection, do not swim in lakes, ponds, streams, rivers, swimming pools and hot tubs while you have diarrhea and until at least 48 hours after the diarrhea has stopped. Avoiding this activity will help to ensure that other swimmers do not become infected.
  • Do not drink unpasteurized milk, and if you are prone to serious illness, avoid unpasteurized juices.


  • Before eating
  • Before handling food
  • After using the toilet or changing diapers
  • After touching animals
    • Make sure children, particularly those who handle pets, wash their hands carefully before eating and on a regular basis if they suck their thumbs or put their hands in their mouths.
    • Avoid contact with fecal matter during sexual activity.

        1. There are two methods to eliminate giardia cysts from water: 
          1. Boiling: Bring water to a rolling boil for at   least one minute and then allow it to cool.  At elevations over 2,000 metres (6,562 feet) you should boil water for at least two minutes to  disinfect.  Boiling will not purify water that is obviously heavily polluted or chemically contaminated. 
          2. Filtering:
          To effectively remove giardia cysts, filters must have an absolute pore size of 1 micron or be rated by the National Sanitation Foundation (NSF) for cyst removal. Cysts are 8 to 12 microns in length and will not pass through a filter pore of 1 micron. Some portable water treatment units used for camping meet the above requirements. 

          Jug-type water filters are not effective in removing giardia. Some built-in water filtration systems will remove giardia, but they need regular and thorough maintenance to work effectively. 

          Other types of water treatment units, such as distillation units and combination (filtration and ultraviolet) units are also available. Check with local water purification suppliers or your local environmental health officer for more detailed information.

          Giardia parasites are resistant to chlorine bleach; If you have no other options, you can attempt to disinfect water with unscented household bleach. Add two drops of bleach per litre (nine drops of bleach per imperial gallon) of untreated water. The treated water should be stirred and allowed to stand for at least 30 minutes prior to use. Double the amount of bleach if the water is cloudy.



Last Updated: March 1, 2012

SOURCE: Giardiasis ( )
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