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Giardiasis (also known as beaver fever) is a disease caused by the flagellate protozoan Giardia lamblia (also Giardia intestinalis). The giardia organism inhabits the digestinal tract of a wide variety of domestic and wild animal species as well as humans. It is a common cause of gastroenteritis in humans, infecting approximately 200 million people worldwide. more...

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Giardiasis is passed via the fecal-oral route. Primary routes are personal contact and contaminated water and food. People who spend time in institutional or day-care environments are more susceptible, as are travelers and those who consume improperly treated water. It is a particular danger to people hiking or backpacking in wilderness areas worldwide. It is zoonotic -- communicable between animals and humans. Major reservoir hosts include beavers, dogs, cats, horses, and cattle.

Symptoms include loss of appetite, lethargy, diarrhea, loose or watery stool, stomach cramps, upset stomach, bloating and flatulence. Symptoms typically begin 1-2 weeks after infection and may wane and reappear cyclically. Symptoms are caused largely by the thick coating of Giardia organisms coating the inside of the small intestine and blocking nutrient absorption. Most people are asymptomatic; only about a third of infected people exhibit symptoms.

Antibiotics used to treat adults include metronidazole, albenzazole and quinacrine. Furazolidone and nitazoxanide may be used in children. Treatment is not always necessary, as the body can defeat the infection by itself.

Outside North America the drug Tinidazole trade name Fagisyn or Tindamax can treat Giardiasis in a single treatment of 2,000 mg. instead of the longer treatment of the other medications listed, with less distress due to the shorter treatment duration.


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From Gale Encyclopedia of Medicine, 4/6/01 by Carol A. Turkington


Giardiasis is a common intestinal infection spread by eating contaminated food, drinking contaminated water, or through direct contact with the organism that causes the disease, Giardia lamblia. Giardiasis is found throughout the world and is a common cause of traveller's diarrhea. In the United States it is a growing problem, especially among children in childcare centers.


Giardia is one of the most common intestinal parasites in the world, infecting as much as 20% of the entire population of the earth. It is common in overcrowded developing countries with poor sanitation and a lack of clean water. Recent tests have found Giardia in 7% of all stool samples tested nationwide, indicating that this disease is much more widespread than was originally believed. It has been found not only in humans, but also in wild and domestic animals.

Giardiasis is becoming a growing problem in the United States, where it affects three times more children than adults. In recent years, giardiasis outbreaks have been common among people in schools or daycare centers and at catered affairs and large public picnic areas. Children can easily pass on the infection by touching contaminated toys, changing tables, utensils, or their own feces, and then touching other people. For this reason, infection spreads quickly through a daycare center or institution for the developmentally disabled.

Unfiltered streams or lakes that may be contaminated by human or animal wastes are a common source of infection. Outbreaks can occur among campers and hikers who drink untreated water from mountain streams. While 20 million Americans drink unfiltered city water from streams or rivers, giardiasis outbreaks from tainted city water have been rare. Most of these problems have occurred not due to the absence of filters, but because of malfunctions in city water treatment plants, such as a temporary drop in chlorine levels. It is possible to become infected in a public swimming pool, however, since Giardia can survive in chlorinated water for about 15 minutes. During that time, it is possible for an individual to swallow contaminated pool water and become infected.

Causes and symptoms

Giardiasis is spread by food or water contaminated by the Giardia lamblia protozoan organism found in the human intestinal tract and feces. When the cysts are ingested, the stomach acid degrades the cysts and releases the active parasite into the body. Once within the body, the parasites cling to the lining of the small intestine, reproduce, and are swept into the fecal stream. As the liquid content of the bowel dries up, the parasites form cysts, which are then passed in the feces. Once excreted, the cysts can survive in water for more than three months. The parasite is spread further by direct fecal-oral contamination, such as can occur if food is prepared without adequate hand-washing, or by ingesting the cysts in water or food.

Giardiasis is not fatal, and about two-thirds of infected people exhibit no symptoms. Symptoms will not occur until between one and two weeks after infection. When present, symptoms include explosive, watery diarrhea that can last for a week or more and, in chronic cases, may persist for months. Because the infection interferes with the body's ability to absorb fats from the intestinal tract, the stool is filled with fat. Other symptoms include foul-smelling and greasy feces, stomach pains, gas and bloating, loss of appetite, nausea and vomiting. In cases in which the infection becomeschronic, lasting for months or years, symptoms might include poor digestion, problems digesting milk, intermittent diarrhea, fatigue, weakness, and significant weight loss.


Diagnosis can be difficult because it can be easy to overlook the presence of the giardia cysts during a routine inspection of a stool specimen. In the past, the condition has been diagnosed by examining three stool samples for the presence of the parasites. However, because the organism is shed in some stool samples and not others, the infection may not be discovered using this method.

A newer, more accurate method of diagnosing the condition is the enzyme-linked immunosorbent assay (ELISA) that detects cysts and antigen in stool, and is approximately 90% accurate. While slightly more expensive, it only needs to be done once and is therefore less expensive overall than the earlier test.


Acute giardiasis can usually be allowed to run its natural course and tends to clear up on its own. Antibiotics are helpful, however, in easing symptoms and preventing the spread of infection. Medications include metronidazole, furazolidone and paromomycin. Healthy carriers with no symptoms do not need antibiotic treatment. If treatment should fail, the patient should wait two weeks and repeat the drug course. Anyone with an impaired immune system (immunocompromised), such as a person with AIDS, may need to be treated with a combination of medications.


Giardiasis is rarely fatal, and when treated promptly, antibiotics usually cure the infection. While most people respond quickly to treatment, some have lingering symptoms and suffer with diarrhea and cramps for long periods, losing weight and not growing well. Those most at-risk for a course like this are the elderly, people with a weakened immune system, malnourished children, and anyone with low stomach acid.


The best way to avoid giardiasis is to avoid drinking untreated surface water, especially from mountain streams. The condition also can be minimized by practicing the following preventive measures:

  • Thoroughly washing hands before handling food
  • Maintaining good personal cleanliness
  • Boiling any untreated water for at least three minutes
  • Properly disposing of fecal material.

Children with severe diarrhea (and others who are unable to control their bowel habits) should be kept at home until the stool returns to normal. If an outbreak occurs in a daycare center, the director should notify the local health department. Some local health departments require a follow-up stool testing to confirm that the person is no longer contagious. People not in high-risk settings can return to their routine activities after recovery.

Key Terms

A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
A substance (usually a protein) identified as foreign by the body's immune system, triggering the release of antibodies as part of the body's defense mechanism.
Enzyme-linked immunosorbent assay (ELISA)
A laboratory technique used to detect specific antigens or antibodies. It can be used to diagnose giardiasis.
A type of protozoa with a whip-like tail that infects the human intestinal tract, causing giardiasis. The protozoa will not spread to other parts of the body.
A state in which the immune system is suppressed or not functioning properly.

Further Reading

For Your Information


  • Bannister, Barbara A., Norman T. Begg, and Stephen H. Gillespie. Infectious Disease. Oxford, England: Blackwell Scientific, Inc., 1996.
  • Turkington, Carol A. Infectious Diseases A to Z. New York: Facts on File, 1998.
  • Van De Graaff, Kent. Survey of Infectious and Parasitic Diseases. New York: McGraw Hill, 1996.
  • Wilks, David, Mark Farrington, and David Rubenstein. The Infectious Diseases Manual. Oxford, England: Blackwell Scientific, Inc., 1995.


  • Hunter, Beatrice Trum. "Giardiasis: The Most Common Parasitic Infection." Consumers' Research Magazine, 76 (4)(April 1993): 8-9.
  • Moser, Penny Ward. "Danger in Diaperland." In Health, 5 (5)(Sept.-Oct. 1991).
  • Pediatrics for Parents editors. "Diarrhea and Day Care Centers." Pediatrics for Parents, (June 1991): 6.
  • Springer, Ilene. "The Summer Vacation Health Guide." Ladies Home Journal, 109 (7)(July 1992): 54-57.
  • Tufts editors. "A Backwoods Parasite Heads for Town." Tufts University Health & Nutrition Letter, 15 (6)(August 1997): 3.


  • Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (404) 639-3311.
  • National Institute of Allergies and Infectious Diseases, Division of Microbiology and Infectious Diseases, Bldg. 31, Rm. 7A-50, 31 Center Drive MSC 2520, Bethesda, MD 20892.
  • World Health Organization, Division of Emerging and Other Communicable Diseases Surveillance and Control. 1211 Geneva 27, Switzerland.


  • Emerging Infectious Diseases Journal, National Center for Infectious Diseases.
  • International Society of Travel Medicine.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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