Giardiasis is an intestinal illness caused by a microscopic parasite called Giardia lamblia. It is a fairly common cause of diarrheal illness. Cases may occur sporadically or in clusters or outbreaks.

Disease Fact Sheet

Disease Facts

Anyone can get giardiasis but it tends to occur more often in people in institutional settings, people in day care centers, foreign travelers and individuals who consume improperly treated surface water (i.e., swallowing water while swimming).

The giardia parasite is passed in the feces of an infected person and may contaminate water or food. Person to person transmission may also occur in day care centers or other settings where hand-washing practices are poor. Animals such as beavers, dogs and cats may also carry giardia.

People exposed to giardia may experience mild or severe diarrhea, gas, abdominal cramps and greasy stools. Some people have no symptoms. Fever is rarely present. Occasionally, some will have chronic diarrhea over several weeks or months, with significant weight loss.

People may become ill 3 to 25 days after exposure but usually within 10 days.

The carrier stage may last from a few weeks to a few months.

Giardia has been found in infected people (with or without symptoms) and wild and domestic animals. Beavers may be a potential source of giardia contamination of lakes, reservoirs and streams, but human fecal wastes are probably most important.

People with active diarrhea who are unable to control their bowel habits (infants, young children, certain handicapped individuals, for example) may need to be excluded from settings such as day care or group activities where they may present a risk to others. After they have been treated and have recovered, they should be permitted to return. Individuals who are not in high-risk settings may return to their routine activities when they have recovered, provided that they carefully wash their hands after each toilet visit. The South Dakota Food Service Code states that a food handler with giardiasis must be excluded from work and may return to work when they obtain approval from the regulatory authority or written approval from a physician.

Anti-parasitic drugs are often prescribed by doctors to treat giardiasis. However, some individuals may recover on their own without medication.

Important preventive measures include:

  • Carefully wash hands thoroughly after toilet visits.
  • Carefully dispose of sewage wastes so as not to contaminate surface or groundwater.
  • Avoid consuming improperly treated drinking water.
  • Boil emergency water supplies. Chemical treatment of emergency drinking water is less reliable.
  • Hunters, backpackers, hikers and campers should not drink un-boiled water directly from rivers, streams or lakes.


This material is provided by the South Dakota Department of Health for informational purposes only and is not a substitute for medical care. We are not able to answer personal medical questions. Please see your health care provider concerning appropriate care, treatment, or other medical advice.

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