Giardiasis definition and prevention


Giardiasis (GEE-are-DYE-uh-sis) is a diarrheal illness caused by a microscopic parasite, Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis). Once a person or animal has been infected with Giardia, the parasite lives in the intestine and is passed in feces. Because the parasite is protected by an outer shell, it can survive outside the body and in the environment for long periods of time. During the past 2 decades, Giardia infection has become recognized as a common cause of waterborne disease in humans in the United States. Giardia can be found worldwide and within every region of the United States.

Other name of the disease

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 this issue.

Causative Agent

Giardia is caused by the parasite Giardia intestinalis (also called Giardia lamblia). The giardia parasite has two forms

Active. The active form of giardia lives in the intestines of an infected animal or human.

Inactive cyst. An inactive cyst form can survive for months in the environment. When you ingest the inactive cysts, their hard shells break down in your stomach, releasing the parasites. The parasites then attach to the wall of your small intestine, eventually reproducing by the millions and damaging the intestinal wall. This interferes with your ability to absorb food, leading to diarrhea and weight loss. In time, the parasites detach from the small intestine, transform back into cysts and are shed in your feces. They can survive in soil or water for long periods until they’re ingested by another host.


Water. This is the main source of giardia infection. The parasites are found in lakes, ponds, rivers and streams worldwide, as well as in municipal water supplies, wells, cisterns, swimming pools, water parks and spas. Giardia parasites have even turned up in touch tanks in aquariums and museums. Ground and surface water can become contaminated from agricultural runoff and wastewater discharge.

Food. Giardia parasites can be transmitted through food — either because food handlers with giardiasis don’t wash their hands or because raw produce is irrigated or washed with contaminated water. Because cooking food kills giardia, food is a less common source of infection than water is, especially in industrialized countries. However, outbreaks can occur through ice and infected food service workers.

Incubation period

Acute giardiasis develops after an incubation period of 1 to 14 days (average of 7 days) and usually lasts 1 to 3 weeks

Mode of transmission

Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites).


Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor.

Clinical Manifestations

The spectrum varies from asymptomatic carriage to severe diarrhea and malabsorption.  Symptoms include diarrhea, abdominal pain, bloating, nausea, and vomiting.  In chronic giardiasis the symptoms are recurrent and malabsorption and debilitation may occur.

Diagnostic Procedure

Your health care provider will likely ask you to submit stool samples to check for the parasite. Because Giardia can be difficult to diagnose, your provider might ask you to submit multiple stool specimens collected over a few days. 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.

Nursing Care


– Practice good hygiene.
– Avoid water that might be contaminated.
– If you are unable to avoid using or drinking water that might be contaminated, then you can make the water safer to drink by boiling, filtration or chlorination.
– Avoid food that might be contaminated.
– Avoid fecal exposure during sexual activity. This is especially important while experiencing diarrhea caused by giardiasis.


When signs and symptoms are severe or the infection persists, doctors usually treat giardiasis with antibiotics such as metronidazole or tinidazole. The two drugs are equally effective, but tinidazole requires a shorter course of treatment. Both can cause side effects such as a metallic taste, nausea and vomiting, and you must avoid drinking alcohol while taking them. Pregnant women shouldn’t use these drugs during the first trimester because they may lead to birth defects. Some doctors prefer not to treat women at all during pregnancy, or they may opt to use the less toxic — though less effective — drug paramomycin. Metronidazole may be considered in extreme cases where signs and symptoms are severe.


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