Health Encyclopedia


What is giardiasis?

Giardiasis is an infection caused by a parasite called Giardia. It causes diarrhea. It is passed on through oral contact with feces. A person can get the parasite by eating food or drinking water that contains feces. When you travel, make sure to not drink water that may be unsafe.

Giardiasis a common intestinal parasite. It is most prevalent in countries where there is poor sanitary conditions, poor water quality control, and overcrowding. However, it is also a common cause of parasitic infection in the U.S. Hikers and campers who drink water from streams and other potentially contaminated sources are often infected.

What causes giardiasis?

The parasite that causes giardiasis lives in two stages:

  • Trophozoites (the active form inside the body)
  • Cysts (the resting stage that enables the parasite to survive outside the body)

Infection begins when the cysts are taken in through contaminated food or water. Stomach acid activates the cysts and the trophozoites are released. They become attached to the lining of the small intestine and reproduce. Cysts form in the lower intestines and are then passed in the feces.

The parasite may be passed from person-to-person by contact with infected feces, or through consuming contaminated food or water.

What are symptoms of giardiasis?

Each person may experience symptoms differently. Symptoms may include:

  • Explosive, watery, foul-smelling stools
  • Greasy stools that tend to float
  • Bloating
  • Nausea
  • Loss of appetite
  • Abdominal (belly) pain
  • Excessive gas
  • Fatigue

The time between infection and the onset of symptoms usually is from 1 to 2 weeks. Some infected people have very mild symptoms or no symptoms at all. The symptoms of giardiasis are a lot like those of other gastrointestinal diseases. Consult a health care provider for diagnosis.

How is giardiasis diagnosed?

Positive diagnosis of giardiasis is made by microscopic identification of the parasite in stool samples. If you think you may have this illness, contact your health care provider for advice.

How is giardiasis treated?

Giardiasis may be treated with prescription medications. Specific treatment for giardiasis will be determined by your health care provider based on:

  • Your overall health and medical history
  • Extent of the disease
  • Your tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the disease
  • Your opinion or preference
Several medications can be used to treat the infection. Effective treatments include metronidazole, tinidazole, and nitazoxanide.

What are the complications of giardiasis?

If the infection is not treated and persists, you may not be able to absorb nutrients. It can also cause unintended weight loss.

Can giardiasis be prevented?

You can prevent giardiasis by practicing good personal hygiene. Proper hygiene when caring for those who may be infected with the parasite is also important. When visiting in an area where giardiasis may exist:

  • Drink only boiled water or bottled water or drinks
  • Avoid ice and beverages made from tap water
  • Do not eat locally-grown uncooked or unpeeled fruits and vegetables

When should I call my health care provider?

Call your health care provider if:

  • Your symptoms get worse or you have new symptoms
  • You lose your appetite and start to lose weight
  • You become dehydrated from prolonged diarrhea

Key points about giardiasis

  • Giardiasis is an infection caused by a parasite called Giardia. It causes diarrhea.
    Symptoms include explosive, watery, greasy, foul-smelling stools, bloating, nausea, pain, gas, fatigue, and loss of appetite.
  • Several medications are available that cure the infection.
  • Prevention includes good personal hygiene, and avoiding drinking water, fruits, and vegetables that may be contaminated with the parasite.

Next steps

Tips to help you get the most from a visit to your health care provider:

  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.

Medical Reviewers:

  • newMentor board-certified, academically affiliated clinician
  • Stump-Sutliff, Kim, RN, MSN, AOCNS