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Giardiasis is not a reportable disease in Oklahoma; however, the Oklahoma State Department of Health investigates outbreaks of Giardiasis to control the spread of this disease. Giardiasis is the name of the illness caused by the parasite Giardia. A person becomes infected by eating or swallowing Giardia cysts. Many infected persons have no symptoms, but shed the infectious cysts without knowing it.

During its lifetime, Giardia organisms have two different forms, a mobile and a dormant stage. Trophozoites are the mobile stage in which the organism feeds and reproduces within its animal host. It is this form of the parasite that causes its host to have diarrheal symptoms. The dormant form is called the cyst. After being swallowed by a host, cysts in the upper small intestine develop into trophozoites. When they occur, symptoms usually begin 3 to 25 days later, although not all infected persons will have symptoms. Infected persons shed trophozoites, cysts or both in stool. Cysts are hardy, and can survive outside the host for months.

There are several different species of Giardia. Recently, taxonomists (scientists who specialize in placing related organisms into ordered species groupings) have proposed changing the name of the Giardia species that causes human disease from Giardia lamblia to G. intestinalis. Currently, discussions and publications regarding this organism occur under both names. Dogs often become ill with related species of Giardia. It is not yet known whether humans are easily infected with this organism. It is not known whether animals play an important role in human infection with Giardia. Beavers, deer, and elk may contaminate surface water such as lakes and streams with Giardia, but how often this results in human infection is not clear.

Symptoms of giardiasis typically include watery, foul-smelling diarrhea that can last for weeks and is accompanied by abdominal cramps, a bloated feeling, and excess gas. Not all infected people experience diarrhea, but may experience nausea, bloating and abdominal pain. Another symptom of giardiasis is decreased fat absorption in the colon, causing fat to appear in the stool.

Once infected with Giardia, people can infect others for months. It is not known to what degree a person is immune to giardiasis after recovering. Giardiasis is diagnosed by identifying it in the stool using special dyes. The test is called an “ova and parasite” or “O and P” test. Culture, used for diagnosing bacterial enteric diseases like salmonellosis, campylobacteriosis, and EHEC, will not yield Giardia for identification.

Many experts believe person-to-person transmission is the most common way people are infected, followed by consumption of contaminated water. Foodborne cases of giardiasis are not as common, but contamination of food by an infected person has the potential to cause large outbreaks.

What can be done to prevent giardiasis?

  • As with all diarrheal illnesses, the best way for individuals to prevent infection is regular hand hygiene.
  • In addition to hand washing after using the bathroom and before and after food preparation, it is important to properly dispose of sewage so water sources will not be infected.
  • Avoid drinking water that has not been properly treated. When camping, treat your drinking water by boiling. If boiling is not possible, two to four drops of household bleach may be added to each liter of water.
  • People with diarrhea should not swim. Protect others by not swimming in pools or other recreational water sources if experiencing diarrhea.
  • When swimming, fishing, water-skiing, or participating in another water-related activity, avoid swallowing water. Do not drink untreated water, such as that from shallow wells, lakes, rivers, ponds, or streams.

Giardiasis Fact Sheets and Information:

Giardia Fact Sheet (39k.pdf) 
  Giardia Hoja Informativa (42k.pdf)

External Giardiasis Resources:

Girardia (CDC)
FirstGov Food Safety

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