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How do I know I have giardia?

  Abdominal cramps and pain Anorexia
  Appetite loss Bloating
  Chills Fatty or greasy stools
  Fever Gas or flatulence
  Growth retardation Inflammation of the digestive tract
  Malabsorption Pale, foul smelling stools that tend to float
  Nausea Upper intestinal pain
  Vomiting Watery or severe diarrhea

The above symptoms may cause weight loss and dehydration. Sometimes they mimic symptoms of a peptic ulcer or gall bladder disease. Many people show no symptoms of giardia infection.

Typically symptoms will start to show 7 days following infection. Symptoms of giardiasis (giardia infection) can last up to weeks, but occasionally longer. Some cases of chronic infection last years.

What is giardia?

Giardia lamblia (intestinalis) is a single-celled organism that infects the intestines of humans and other animals.

Giardia (also known as Lamblia intestinalis) reproduce in their host and spread by being passed in feces. Because this parasite is protected by an outer shell it can survive for months outside of the body in the environment before re-infecting another individual.

The disease caused by giardia infection is known as giardiasis (or beaver fever in some parts of the United States). Little is known about how the parasite actually causes illness, but some researchers have suggested that the parasite may inhibit the intestinal wall from absorbing nutrients. Others believe the parasite produces a toxin, although its existence is yet to be confirmed.

Unlike bacterial infections where it may be necessary for thousands of organisms to cause disease, giardiasis can be caused by the ingestion of just one parasitic cyst.

A study completed in 2009 indicates that there are actually several strains of Giardia lamblia, with researchers in Sweden identifying seven main genetic groups of the parasite. Two of these strains are known to infest humans with major genetic differences noted between them, causing different sets of symptoms.

Giardia is now recognized as one of the most common causes of water-borne illness in the world, and to be a frequent cause of food-borne illness as well. Infection usually results from drinking water contaminated with giardia, although infections are commonly seen in day care centers and among campers.

How did I get infected?

Giardia lives in the intestine of infected humans and animals, including dogs, cats, cattle, deer, beavers, etc. The parasite is released into the environment through bowel movements, and can be found in soil, food or water that has come into contact with contaminated feces.

Infection occurs when a giardia cyst is accidentally swallowed.

The most common ways of contracting a giardia infection though contaminated water are:

  • Drinking water from lakes, streams or wells
  • Consuming ice made from contaminated water
  • Swallowing water from swimming pools, water parks, hot tubs, fountains, lakes, rivers, springs, ponds, streams, swimming holes during recreational use
  • Taking contaminated water or ice while traveling in regions where giardia are common

Other ways of contracting a giardia infection include:

  • Contact with contaminated surfaces (bathroom fixtures, changing tables, diapers, toys, litter trays, etc.)
  • Eating uncooked contaminated food
  • Having contact with an infected person

People most likely at risk include:

  • Children who wear diapers
  • Children in child care
  • Family members of infected persons
  • People who come into contact with infected animals
  • Backpackers, hikers, campers and international travelers that drink insufficiently treated water
  • People who practice insufficient hygiene (e.g. washing of hands after using toilet or before handling food)
  • Swimmers who use lakes, rivers, ponds, water holes
  • People exposed to human feces through sexual contact

Giardia is extremely adept at spreading infection. Cysts are infectious as soon as they are released through feces, and can remain infectious for months. Infected persons have been reported as shedding 1 billion cysts per day, and to continue doing so for months.

During the 1990's giardia was identified as causing 9.4% of all gastroenteritis outbreaks associated with recreational water use, and 16.2% of all outbreak associated with drinking water.


Giardia causes diarrhea in 250 million people each year, being found worldwide both in developing and developed countries. Outbreaks are reported regularly throughout many affluent lands including Western Europe and Australia, and since the 1990's has been recognized as one of the most common causes of waterborne disease in every region of the United States. Giardia is acknowledged as the most frequent cause of non-bacterial diarrhea in North America.

Giardiasis is more prevalent in children, particularly those who wear diapers or are in child care. Recurring symptomatic giardiasis is more common in adults however.

Homosexual men also see higher rates of infection, both in HIV-positive and HIV-negative individuals. 25% of all cases of gastroenteritis may be attributed to giardia infection.

Giardia infects approximately 2.5 million person in the United States each year, making it the most common intestinal parasite in that country.

Is giardia infestation dangerous?

Effects of giardia infection are often limited to digestive problems, but giardiasis has been associated with the onset of reactive arthritis and liver inflammation (granulomas), and can be life-threatening for individuals with immune deficiencies.

In cases of prolonged giardia infection, diarrhea and impaired intestinal absorption can result in significant loss of fluids and nutrients. This in turn can cause severe weight loss and debility from malnutrition. In infants this can be life threatening.

About 40% of people diagnosed with giardiasis develop sugar intolerance, especially to lactose (milk sugar). This condition requires avoiding lactose, sucrose and maltose, and may persist for up to 6 months after the parasite is eliminated.

Can I prevent giardia infestation?

As the giardia parasite survives in cyst form outside the host's body, it essentially is protected by an outer shell that allows it to live in the environment for months before re-infection. Also, whereas bacterial infections require hundreds or even thousands of organisms to infect before causing disease, giardiasis can be caused by ingesting just one single organism.

These factors contribute to the contagious nature of giardia, making it extremely challenging to prevent infections.

Nevertheless the following precautions, while not guaranteeing total protection, can minimize the spreading of infection:

  • Do not drink untreated water from shallow wells, lakes, rivers, streams, springs, ponds, etc.
  • Avoid untreated water or ice made from untreated water in regions with giardia outbreaks or in countries where the water supply may be suspect
  • When using suspect water is unavoidable, boil water for at least 1 minute, or 3 minutes in higher altitude areas over 2000 meters (6,562 feet), or filter water through a 1 micron size filter or filter that is rated for cyst removal
  • Wash in safe water and peel all raw fruit and vegetables before eating
  • Avoid eating uncooked foods (including salads) in countries with insufficient water treatment systems
  • Do not swallow recreational water
  • Practice good hygiene - washing hands after using the toilet and before handling food
  • Wash your hands and your child's hands after changing diapers or assisting them with toileting
  • Wash hands thoroughly after touching surfaces that may be contaminated, including trash cans, cleaning cloths, drains, soil, or animals and their toys, leashes, litter trays or cleaning their feces
  • Do not swim in recreational water (pools, hot tubs, lakes, rivers, the ocean, etc.) for up to one week after giardia-related diarrhea ceases. (You or your child can pass infection even after symptoms cease)
  • Shower with soap and water before swimming in recreational water. Wash children thoroughly, especially their bottoms, after they use the toilet or their diapers are changed and before they enter the water
  • While swimming, take children on frequent toilet breaks and check their diapers often. Change diapers only in bathrooms or diaper changing areas
  • Avoid fecal exposure during sexual activity, especially while experiencing giardia-related diarrhea
  • Keep your child out of child care until well after symptoms of giardiasis cease


Can I be safely treated for giardia?

Treating giardiasis involves both the elimination of the parasite, and the treatment of symptoms that may continue for months after the infection has ceased.

As one of the universal symptoms of giardiasis is diarrhea, treatment should always involve a regime of replacing fluids and nutrients, including beneficial bacteria and minerals (electrolytes). This is particularly critical for infants as rapid loss of fluids from diarrhea can be life threatening.

Young children and pregnant women may also be more susceptible to diarrhea-related dehydration.

Holistic herbal treatments that subscribe to the philosophy of weed, seed and feed thus lend themselves well to treating giardia infection and its associated effects. Herbs such as clove, garlic and olive leaf have demonstrated an effective anti-protozoan action both in recorded traditions and in scientific testing, while barberry has shown in testing particular effectiveness against giardia. Practitioners trained in natural medicine prescribe wellness programs that include probiotics and minerals to "seed" and "feed" the system - replacing what was lost.

The availability of reliable and effective herbal treatments is now greater than ever. Scientific advancements enhance the understanding of how phytochemicals in these herbs work to eliminate parasites like giardia. Pharmaceutical-grade manufacturing requirements in the highly regulated industries of Australia and Germany ensure safe and effective natural medicines are readily available.

Alternative: Despite being an antibiotic (aimed at killing bacteria), metronidazole (Flagyl) remains one of the most commonly prescribed drugs for giardia (a protozoa, not a bacteria). Metronidazole shows good results in terminating giardia infections. Individuals with chronic giardiasis remain difficult to treat, and frequently see limited success with this drug.

This page is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care professional. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care professional.


Center for Disease Control, Division of Parasitic Diseases: Giardiasis Factsheet
Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Giardia lamblia US Food & Drug Administration May 4, 2009
Hlavsa M.C., Watson J.C., Beach M.J. Giardiasis Surveillance --- United States, 1998--2002 Morbidity and Mortality Weekly Report January 28, 2005 / 54(SS01);9-16
"Giardia found in Sydney water supplies" Sydney Morning Herald June 27, 2007
Katanik M.T., Schneider S.K., Rosenblatt J. E., Hall G. S., Procop G. W. Evaluation of ColorPAC Giardia/Cryptosporidium Rapid Assay and ProSpecT Giardia/Cryptosporidium Microplate Assay for Detection of Giardia and Cryptosporidium in Fecal Specimens Journal of Clinical Microbiology, December 2001, p. 4523-4525, Vol. 39, No. 12
Chevallier A. Encyclopedia of Medicinal Plants. Revised Edition. Sydney, Australia: Dorling Kindersley. 2001.
Duke JA, et. al. Handbook of Medicinal Herbs. Second Edition. Boca Raton, FL: CRC Press. 2002.
Jellin JM, Batz F, Hitchens K. Natural Medicines Comprehensive Database. Third Edition. Stockton, California: Therapeutic Research Faculty, 2000.
Barnes J, Anderson LA, Phillipson JD, Herbal Medicines: A Guide for Healthcare Professionals. Second Edition. London: Pharmaceutical Press, 2002.
Ross I. Medicinal Plants of the World: Chemical Constituents, Traditional and Modern Medicinal Uses. Totowa: Humana Press, 1999.

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