giardiasis jēärdīˈəsĭs, järdīˈəsĭs [key], 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.

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