Giardiasis is a major diarrheal disease found throughout the world. The flagellate protozoan Giardia intestinalis (previously known as G lamblia), as shown in the picture above is its causative agent, is the most commonly identified intestinal parasite in the United States and the most common protozoal intestinal parasite isolated worldwide. Infection is more common in children than in adults.
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. 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.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.