Causal Agent: Life Cycle:

<strong>Causal</strong> <strong>Agent</strong>:<br />

Giardia intestinalis is a protozoan flagellate (Diplomonadida). This protozoan was initially named<br />

Cercomonas intestinalis by Lambl in 1859 and renamed Giardia lamblia by Stiles in 1915, in honor<br />

of Professor A. Giard of Paris and Dr. F. Lambl of Prague. However, many consider the name,<br />

Giardia intestinalis, to be the correct name for this protozoan. The International Commission on<br />

Zoological Nomenclature is reviewing this issue.<br />

<strong>Life</strong> <strong>Cycle</strong>:<br />

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and<br />

trophozoites can be found in the feces (diagnostic stages) . The cysts are hardy and can survive

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several months in cold water. Infection occurs by the ingestion of cysts in contaminated water,<br />

food, or by the fecal-oral route (hands or fomites) . In the small intestine, excystation releases<br />

trophozoites (each cyst produces two trophozoites) . Trophozoites multiply by longitudinal<br />

binary fission, remaining in the lumen of the proximal small bowel where they can be free or<br />

attached to the mucosa by a ventral sucking disk . Encystation occurs as the parasites transit<br />

toward the colon. The cyst is the stage found most commonly in nondiarrheal feces . Because<br />

the cysts are infectious when passed in the stool or shortly afterward, person-to-person<br />

transmission is possible. While animals are infected with Giardia, their importance as a reservoir is<br />

unclear.<br />

Geographic Distribution:<br />

Worldwide, more prevalent in warm climates, and in children.<br />

Clinical Features:<br />

The spectrum varies from asymptomatic carriage to severe diarrhea and malabsorption. Acute<br />

giardiasis develops after an incubation period of 1 to 14 days (average of 7 days) and usually lasts<br />

1 to 3 weeks. Symptoms include diarrhea, abdominal pain, bloating, nausea, and vomiting. In<br />

chronic giardiasis the symptoms are recurrent and malabsorption and debilitation may occur.<br />

Laboratory Diagnosis:<br />

Giardiasis is diagnosed by the identification of cysts or trophozoites in the feces, using direct<br />

mounts as well as concentration procedures. Repeated samplings may be necessary. In addition,<br />

samples of duodenal fluid (e.g., Enterotest) or duodenal biopsy may demonstrate trophozoites.<br />

Alternate methods for detection include antigen detection tests by enzyme immunoassays, and<br />

detection of parasites by immunofluorescence. Both methods are available in commercial kits.<br />

Diagnostic findings<br />

• Microscopy<br />

• Molecular methods<br />

• Bench aid for Giardia<br />

Treatment:<br />

Several prescription drugs are available to treat giardiasis including metronidazole and<br />

tinidazole. Nitazoxanide has provided some encouraging results in the management of giardiasis in<br />

children