What is giardiasis?

Updated: Oct 01, 2018
  • Author: Hisham Nazer, MBBCh, FRCP, DTM&H; Chief Editor: Burt Cagir, MD, FACS  more...
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Giardiasis is a major diarrheal disease found throughout the world. The flagellate protozoan Giardia intestinalis­­ (previously known as G lamblia or G duodenalis), its causative agent, is the most commonly identified intestinal parasite in the United States [1, 2] and the most common protozoal intestinal parasite isolated worldwide. [3, 4, 5, 6, 7] Infection is more common in children than in adults. [8, 9]

G intestinalis can cause asymptomatic colonization or acute or chronic diarrheal illness. The organism has been found in as many as 80% of raw water supplies from lakes, streams, and ponds and in as many as 15% of filtered water samples. [10, 11] It is a common cause of chronic diarrhea and growth retardation in children in developing countries.

Giardiasis usually represents a zoonosis with cross-infectivity between animals and humans. Giardiaintestinalis has been isolated from the stools of beavers, dogs, cats, and primates. Beavers may be an important reservoir host for G intestinalis. [12, 13, 14] Other Giardia species include G muris in rodents; G agilis in amphibians; G psittaci and G ardeae in birds; and G microti in voles and muskrats. [15, 16, 17]

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