Causes and Symptoms of Giardiasis - Minnesota Dept. of Health

Causes and Symptoms of Giardiasis

Giardiasis is a diarrheal illness caused by Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis), a one-celled, microscopic protozoan parasite

The parasite is passed in the stool of an infected person or animal. The parasite is protected by an outer shell that allows it to survive outside the body and in the environment for long periods of time.

During the past 2 decades, Giardia has become recognized as one of the most common causes of waterborne illness (drinking and recreational) in humans in the United States. Approximately 620 to 1400 cases of giardiasis are reported to the Minnesota Department of Health each year.

On this page:
Fact Sheets
Duration of Illness

Fact Sheet


Common symptoms include:

  • watery diarrhea
  • greasy stools that can float
  • gas and bloating
  • stomach cramps
  • loss of appetite
  • weight loss
  • and a slight fever.

Some people have no symptoms.

Symptoms generally begin 1 to 3 weeks after infection. Some people can be infected but have no symptoms.

Duration of Illness

  • Symptoms last about 2 to 6 weeks in healthy persons.


Giardia lives in the intestine of infected humans or animals. Millions of germs can be released in a bowel movement from an infected human or animal. You can become infected after accidentally ingesting the parasite.

Giardia may be found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals.

  • Common ways Giardia is transmitted include:
    • Swallowing contaminated water while swimming or drinking.
    • Having contact with persons who are ill with giardiasis, especially in child care settings.
    • Eating foods contaminated with the parasite.
    • Swallowing Giardia organisms picked up from contaminated surfaces, like changing tables, door handles, and toys. 

Do you suspect that you have a foodborne or waterborne illness? Visit reporting suspected foodborne/waterborne illnesses.

Updated Tuesday, 14-Nov-2017 14:10:46 CST