[jee-ahr-dahy-uh-sis, jahr-]
giardiasis, infection of the small intestine by a protozoan, Giardia lamblia. Giardia, which was named after Alfred M. Giard, a French biologist, is spread via the fecal-oral route, most commonly by eating food contaminated by the unwashed hands of an infected person or by drinking groundwater polluted by the feces of infected animals such as dogs and beavers (hence the nickname "beaver fever"). It attaches itself to the walls of the small intestine and there multiplies quickly. About two thirds of infected individuals develop no symptoms. Symptoms, when present, occur one to three days after infection and consist of diarrhea, flatulence, and abdominal cramps, often accompanied by weight loss. In some cases the infection becomes chronic. Giardiasis has traditionally been considered a tropical disease, but it is becoming more common in developed countries, especially among gay men and among groups of very young children in close contact with each other, as in day-care centers before toilet training and proper handwashing techniques have been mastered. Diagnosis is by direct microscopic examination of the stool or by testing for antibodies to the parasite. In most cases no treatment is necessary. The drugs metronidazole, tinidazole, and nitazoxanide are sometimes prescribed.
Giardiasis — popularly known as beaver fever or backpacker's diarrhea — is a disease caused by the flagellate protozoan Giardia lamblia (also sometimes called Giardia intestinalis and Giardia duodenalis). The giardia organism inhabits the digestive tract of a wide variety of domestic and wild animal species, including humans. It is a common cause of gastroenteritis in humans, infecting approximately 200 million people worldwide.


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. Giardia is suspected to be zoonotic—communicable between animals and humans. Major reservoir hosts include beavers, dogs, cats, horses, cattle and birds.


Symptoms include loss of appetite, lethargy, fever, explosive diarrhea, hematuria (blood in urine), loose or watery stool, stomach cramps, upset stomach, projectile vomiting (uncommon), bloating, flatulence, and burping (often sulphurous). Symptoms typically begin 1–2 weeks after infection and may wane and reappear cyclically. Symptoms are caused by 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. Untreated, symptoms may last for six weeks or longer.

Symptomatic infections are well recognised as causing lactose intolerance, which, while usually temporary, may become permanent. Although hydrogen breath tests indicate poorer rates of carbohydrate absorption in those asymptomatically infected, such tests are not diagnostic of infection. It has been suggested that these observations are explained by symptomatic giardia infection allowing for the overgrowth of other bacteria.

Some studies have shown that giardiasis should be considered as a cause of Vitamin B12 deficiency, this a result of the problems caused within the intestinal absorption system.


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

The drug tinidazole can treat giardiasis in a single treatment of 2000 mg, instead of the longer treatment of the other medications listed. The shorter duration of treatment may also cause less patient distress. Tinidazole is now approved by the FDA and available to U.S. patients.

Lab Diagnosis

  • The mainstay of diagnosis of Giardiasis is stool microscopy. This can be for motile trophozoites or for the distinctive oval G.lamblia cysts.
  • The entero-test uses a gelatin capsule with an attached thread. One end is attached to the inner aspect of the patient's cheek, and the capsule is swallowed. Later the thread is withdrawn and shaken in saline to release trophozoites which can be detected microscopically.
  • A new immunologic test referred to as ELISA, for enzyme-linked immunosorbent assay is now available. These tests are capable of a 90 percent detection rate or more.
  • Because Giardia lamblia is difficult to detect, often leading to misdiagnoses, it is advised that several tests be conducted over a one week time period.


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