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Chapter 9


Giardia lamblia (also known as Giardia duodenalis) is one of the most common intestinal parasites of man and is worldwide in distribution. Van Leeuwenhoek, in a 1681 letter written to Hooke at the Royal Society, accurately described the motile trophozoite of G. lamblia which he found in his own stool, as " animalcules a-moving very prettily. . . Their bodies were somewhat longer than broad, and their belly, which was flatlike, furnisht with sundry little paws . . . yet for all that they made but slow progress." In 1859, Lambl gave a full illustrated description of the parasite, and Stiles named it Giardia lamblia in 1915; the details of its morphology were elucidated by Simon in 1921.

Until 1968 it was thought that this ubiquitous organism did not cause significant inflammatory changes in the mucosa of the duodenum and jejunum (its usual habitat) and that there were no specific radiological manifestations of giardiasis. Studies since then have shown that neither of these prior assumptions is true, and giardiasis is now recognized as a significant cause of diarrhea, malabsorption and inflammatory changes in the proximal small bowel in many patients throughout the world, especially in children or those with immunoglobulin deficiencies. It is now one of the ten major parasitic diseases affecting humans, especially in the tropics, and it is of increasing importance in the developed world as an endemic cause of diarrhea and one of the etiologies of travelers' diarrhea. It must be remembered, however, that the vast majority of people harboring Giardia show no clinical or radiological manifestations of their infection.


Giardiasis. Giardia lamblia infection. Giardia duodenalis infection. Giardia intestinalis infection. Megastoma entericum. Sp: Lamblia intestinalis. Fr: Giardia de Lambli. Ger: Lamblia intestinalis. Dünndarmflagellat.


Giardiasis is a parasitic infection of the small intestine, usually the duodenum and jejunum, by the protozoan Giardia lamblia. It can occur as an active infection, but most people harbor the organisms in a carrier state.

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