is a protozoan flagellate (Diplomonadida). This protozoan was initially
named Cercomonas intestinalis by Lambl in 1859 and renamed
Giardia lamblia by Stiles in 1915, in honor of Professor A. Giard of
Paris and Dr. F. Lambl of Prague. However, many consider the name,
Giardia intestinalis, to be the correct name for this protozoan.
The International Commission on Zoological Nomenclature is reviewing
resistant forms and are responsible for transmission of giardiasis.
Both cysts and trophozoites can be found in the feces (diagnostic
The cysts are hardy and can survive several months in cold water.
Infection occurs by the ingestion of cysts in contaminated water, food,
or by the fecal-oral route (hands or fomites)
In the small intestine, excystation releases trophozoites (each cyst
produces two trophozoites)
Trophozoites multiply by longitudinal binary fission, remaining in the
lumen of the proximal small bowel where they can be free or attached to
the mucosa by a ventral sucking disk
Encystation occurs as the parasites transit toward the colon. The cyst
is the stage found most commonly in nondiarrheal feces
Because the cysts are infectious when passed in the stool or shortly
afterward, person-to-person transmission is possible. While animals are
infected with Giardia, their importance as a reservoir is
Worldwide, more prevalent in warm climates, and in children.
spectrum varies from asymptomatic carriage to severe diarrhea and
malabsorption. Acute giardiasis develops after an incubation period of
1 to 14 days (average of 7 days) and usually lasts 1 to 3 weeks.
Symptoms include diarrhea, abdominal pain, bloating, nausea, and
vomiting. In chronic giardiasis the symptoms are recurrent and
malabsorption and debilitation may occur.
Giardiasis is diagnosed by the identification of cysts or trophozoites
in the feces, using direct mounts as well as concentration procedures.
Repeated samplings may be necessary. In addition, samples of duodenal
fluid (e.g., Enterotest) or duodenal biopsy may demonstrate trophozoites.
Alternate methods for detection include antigen detection tests by
enzyme immunoassays, and detection of parasites by immunofluorescence.
Both methods are available in commercial kits.
Bench aid for
prescription drugs are available to treat giardiasis including
metronidazole and tinidazole. Nitazoxanide has provided some
encouraging results in the management of giardiasis in children.