Giardiasis (beaver fever)

Last Reviewed: January 2022

What is giardiasis?

Giardiasis is an intestinal (bowel) illness caused by a microscopic parasite called Giardia lamblia. It is a common illness that causes diarrhea (loose stool/poop).

Who gets giardiasis?

Anyone can become infected with Giardia, but infection occurs more often in children and staff in daycare centers, foreign travelers, and people who drink improperly treated surface water. Men who have sex with men may also be at increased risk of getting giardiasis.

How is this parasite spread?

Giardia can infect people and wild and domestic animals. It is passed in the feces (poop) of an infected person or animal and may contaminate water or food. The beaver has gained attention as a potential source of Giardia contamination of lakes, reservoirs, and streams, but human fecal wastes are also play an important role in spreading the parasite. People become infected by accidently swallowing Giardia and can carry the parasite in their bodies from a few weeks to a few months. Spread of the parasite directly from one person to another may occur in daycare centers or other settings where handwashing practices are poor or through oral-anal sex.

What are the symptoms of giardiasis and how soon do they appear?

People exposed to Giardia may experience mild or severe diarrhea (loose stool/poop), gas, stomach cramps, nausea (a feeling of upset in the stomach), or dehydration (loss of water in the body causing weakness of dizziness). Some people experience no symptoms at all. Fever is rarely present. Occasionally, some people will have chronic diarrhea over several weeks or months, with significant weight loss.

The symptoms may appear from 3 to 25 days after exposure but usually within 7-14 days.

How is giardiasis diagnosed?

Giardiasis is diagnosed by testing samples of your stool (poop). Sometimes, several different stool samples must be tested because the number of Giardia being passed in the stool, which varies from day to day, may be too low to detect from any single sample.

What is the treatment for giardiasis?

Doctors commonly treat giardiasis by prescribing antibiotics such as metronidazole, tinidazole, or nitazoxanide. However, some individuals may recover on their own in a few weeks without medication.

What can be done to prevent the spread of giardiasis?

Three important preventive measures are:

  • Carefully wash hands thoroughly with soap and water after toilet visits and handling soiled diapers.
  • Carefully wash hands with soap and water after working with soil (landscaping, field work, gardening, etc.)
  • Carefully dispose of sewage wastes so as not to contaminate surface water or groundwater.
  • Avoid consuming untreated water from springs, streams, or lakes.

Should an infected person be excluded from work or school?

People with active diarrhea (loose stool/poop) who are unable to control their bowel movements (infants and young children for example) may need to be excluded from settings such as daycare or group activities where they may present a risk to others. After they have been treated and have recovered, they may be allowed to return. Food handlers may not work while ill with giardiasis. In addition, some local health departments may require follow-up stool (poop) sample testing to confirm that the person is no longer contagious. Individuals who are not in high-risk settings may return to their routine activities when they have recovered, if, they carefully wash their hands with soap and water after each toilet visit.