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What Is Giardiasis?

Giardiasis, a top cause of diarrhea, is an intestinal illness that can pass easily from person to person.

What Causes Giardiasis?

Giardiasis (jee-are-DYE-uh-sis) is caused by the tiny Giardia parasite. The parasite attaches itself to the lining of the small intestines in humans, where it causes diarrhea and blocks the body's absorption of fats and carbohydrates from digested foods.

How Does Giardiasis Spread?

Giardiasis is very contagious, and can spread easily:

  • among family members
  • in childcare centers or other facilities caring for groups of people
  • among people who are traveling

This can happen:

  • if someone who's infected doesn’t wash their hands well after going to the bathroom or changing diapers
  • through water contaminated with the stool (poop) of someone who's infected. The poop of some animals with a giardia infection can contaminate water. So be especially careful when camping or hiking.
  • through uncooked foods contaminated by soil or foods that were rinsed in contaminated water

In developing countries, giardiasis is a major cause of diarrhea. But even people in developed countries can get the infection, especially children younger than 5.

Young kids are more likely to have giardiasis than adults. But it isn't unusual for an entire family to be infected, with some family members having diarrhea, some just crampy belly pains, and some with no symptoms.

What Are the Signs & Symptoms of Giardiasis?

Many people with giardiasis have no signs or symptoms of illness, even though they are infected.

When the parasite does cause symptoms, the illness usually begins with severe watery diarrhea. Then, the stool becomes greasy and smells very bad.

Other symptoms include:

  • abdominal cramps
  • low energy (malaise)
  • lots of intestinal gas
  • an enlarged belly from the gas
  • loss of appetite
  • nausea and vomiting
  • sometimes a low-grade fever

These symptoms may last for 1–6 weeks. They can last longer in some people, or get better and come back. If symptoms last a while, a child may lose weight or show other signs of poor nutrition.

How Is Giardiasis Diagnosed?

Doctors confirm the diagnosis of giardiasis by having stool samples checked for Giardia parasites. Sometimes it is hard to find the giardia in one sample, so doctors may send more than one to the lab.

How Is Giardiasis Treated?

Doctors usually treat giardiasis with prescription medicines that kill the parasites.

If your child has giardiasis, be sure to give all doses on schedule for as long as your doctor directs. This will help your child recover faster and will kill parasites that might infect others in your family. Encourage all family members to wash their hands well and often, especially after using the bathroom and before eating or preparing food.

Ask the doctor before you give your child any nonprescription drugs for cramps or diarrhea because these medicines may hide symptoms and interfere with treatment.

How Long Does Giardiasis Last?

Most kids are better within a week of taking medicine to kill the parasites. Medicine also shortens the time that they're contagious. If giardiasis isn't treated, symptoms can last up to 6 weeks or longer.

Can Giardiasis Be Prevented?

Some food safety and hygiene precautions can help prevent giardiasis. To help protect your family:

  • Drink only from water supplies that have been approved by local health authorities.
  • Bring your own water when you go camping or hiking. Never drink from sources like mountain streams. Or boil water for at least 10 minutes.
  • Wash raw fruits and vegetables in clean water before you eat them.
  • Wash your hands before you cook food for yourself or for your family.
  • Teach kids to wash their hands after every trip to the bathroom and especially before eating.
  • Wash your hands well and often if you're caring for someone who has giardiasis.
  • Have your kids wash their hands after handling or playing in water like lakes, ponds, rivers, streams, or aquariums. 
  • Always wash your hands after changing a diaper.
  • Have your water checked on a regular basis if it comes from a well.
  • Anyone with diarrhea should not go swimming in a pool, especially infants and toddlers in diapers. 

When Should I Call the Doctor?

Call the doctor if your child has:

  • lots of diarrhea, especially if they also have a fever, belly pain, or don’t want to eat or drink
  • signs of dehydration, such as drowsiness, sunken eyes, a dry mouth, no tears, or fewer wet diapers than usual
  • blood in the diarrhea
  • diarrhea and weight loss

You know your child best. Call the doctor if your child has any other signs that concern you.

Reviewed by: Melanie L. Pitone, MD
Date Reviewed: Nov 5, 2022

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