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Giardia (say "gee-ar-dee-ah") is the name of a microscopic parasite that can live in the human bowel. The sickness that this parasite causes is called giardiasis (say "gee-ar-dye-a-sis").

Giardiasis, also called Giardia enteritis and lambliasis, is a protozoal infection of the small bowel.

Giardiasis occurs worldwide but is most common in developing countries and other areas where sanitation and hygiene are poor.

In the United States, giardiasis most frequently occurs in travelers who have recently returned from endemic areas, campers who drink non-purified water from contaminated streams, male homosexuals, patients with congenital IgA deficiency, and children in day-care centers. Children in general are more likely to develop giardiasis than adults, probably because of frequent hand-to-mouth activity. Over the past 10 years, the parasite responsible for the disease has been found in municipal water sources, nursing homes, and day-care centers.

The prognosis is good; with treatment, the patient recovers completely. Without treatment, symptoms continue to wax and wane. Also, giardiasis doesn't confer immunity, so re-infections can occur.


Giardiasis is caused by the symmetrical flagellate protozoan Giardia lamblia, which has two stages: the cystic stage and the trophozoite stage. Ingestion of G. lamblia cysts in stool-contaminated water or the fecal-oral transfer of cysts by an infected person results in giardiasis.

When cysts enter the small bowel, they release trophozoites, which attach themselves with their sucking disks to the bowel's epithelial surface. This attachment causes superficial mucosal invasion and destruction, inflammation, and irritation. After that, the trophozoites encyst again, travel down the colon, and are excreted. Unformed stool that pass quickly through the intestine may contain trophozoites as well as cysts.

Signs and symptoms

The signs and symptoms of giardiasis are similar to those of other intestinal illnesses:

  • Diarrhea
  • Abdominal cramps
  • Nausea

These symptoms can lead to weight loss and dehydration (loss of fluids). However, not all infected persons have symptoms.

Diagnostic tests 

Doctors confirm the diagnosis of giardiasis by finding Giardia parasites in an infected person's stool (poop). Stool samples are sent to the laboratory for examination. Several samples may be needed before the parasites are found.

Less often, doctors make the diagnosis by looking at the lining of the small intestine with an instrument called an endoscope and taking samples from inside the intestine to be sent to a laboratory. This is done in more extreme cases, when a definite cause for the diarrhea hasn't been found.


Giardiasis responds readily to metronidazole. Some patients (such as children) may instead be given furazolidone, but it isn't as effective. If the patient has severe diarrhea and oral fluid intake is inadequate, he may need parenteral fluid replacement to prevent dehydration.


Here are some ways you can protect your family from giardiasis:

  • Water purification methods such as boiling, filtration, and iodine treatment should be used when surface water is used. Hikers or others using surface water should consider all sources as potentially contaminated.
  • Wash your hands well before you cook food for yourself or for your family.
  • Workers in day-care centers or institutions should use good handwashing and hygiene techniques when going from child to child or patient to patient.
  • Wash raw fruits and vegetables well before you eat them.
  • Safer sexual practices, especially regarding anal sex, may decrease the risk of contracting or spreading giardiasis.

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