Giardiasis (beaver fever)

Last Reviewed: October 2011

What is giardiasis?

Giardiasis is an intestinal illness caused by a microscopic parasite called Giardia lamblia. It is a fairly common cause of diarrheal illness and it is estimated that over 2,000 cases occur in New York State each year. Cases may occur sporadically or in clusters or outbreaks.

Who gets giardiasis?

Anyone can get giardiasis but it tends to occur more often in people in institutional settings, people in daycare centers, foreign travelers and individuals who consume improperly treated surface water. Men who have sex with men may also be at increased risk of contracting giardiasis.

How is this parasite spread?

The Giardia parasite is passed in the feces of an infected person or animal and may contaminate water or food. Person-to-person transmission may also occur in daycare centers or other settings where handwashing practices are poor.

What are the symptoms of giardiasis?

People exposed to Giardia may experience mild or severe diarrhea, or in some instances no symptoms at all. Fever is rarely present. Occasionally, some will have chronic diarrhea over several weeks or months, with significant weight loss.

How soon do symptoms appear?

The symptoms may appear from 3 to 25 days after exposure but usually within 10 days.

For how long can an infected person carry Giardia?

The carrier stage generally lasts from a few weeks to a few months. Treatment with specific antibiotics may shorten the carrier stage.

Where are Giardia parasites found?

Giardia has been found in infected people (with or without symptoms) and wild and domestic animals. The beaver has gained attention as a potential source of Giardia contamination of lakes, reservoirs and streams, but human fecal wastes are probably as important.

What is the treatment for giardiasis?

Antibiotics such as metronidazole, tinidazole, nitazoxanide or furazolidone are often prescribed by doctors to treat giardiasis. However, some individuals may recover on their own without medication.

Should an infected person be excluded from work or school?

People with active diarrhea who are unable to control their bowel habits (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 permitted to return. In addition, some local health departments may require follow-up stool 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, provided that they carefully wash their hands after each toilet visit.

What can a person or community do to prevent the spread of giardiasis?

Three important preventive measures are:

  • Carefully wash hands thoroughly after toilet visits.
  • Carefully dispose of sewage wastes so as not to contaminate surface water or groundwater.
  • Avoid consuming untreated water from springs, streams or lakes.