What is Giardia?
Giardia intestinalis is a microscopic parasite (too small to see with the naked eye). It can affect humans and animals, such as dogs, cats and wild animals. A parasite is an organism that needs another organism (like a person or animal) to survive.
What is giardiasis?
Giardiasis (JEE-are-die-uh-sis) an infection caused by the parasite Giardia. After someone comes into contact with the parasite, the parasite can live in their intestines. It may make you sick.
How common is giardiasis?
Giardia parasites live around the world, in most countries and continents. It tends to be a bigger problem in countries with poor sanitation, such as developing countries. But you can get it almost anywhere.
In the United States, giardiasis is the most common parasitic infection to affect the intestines.
Symptoms and Causes
What causes giardiasis?
Giardiasis is caused by the parasite Giardia intestinalis.
How is giardiasis spread?
Giardiasis can spread through food or water. It also spreads via surfaces contaminated with Giardia cysts, or hard shells that contain the parasite. Even though parasites need a host (another living thing) to survive, Giardia's shell enables the parasite to live on its own for extended periods.
People commonly get giardiasis from swallowing the parasite in untreated water. Giardiasis travels in even trace amounts of infected stool (poop) — amounts so small you can’t see it. If you have giardiasis, you can spread it to someone else, even if you have no symptoms.
You can get giardiasis through:
- Drinking from untreated water sources (such as lakes, streams or swimming pools).
- Traveling to countries with poor sanitation practices.
- Working closely with young children (such as in a child care center).
- Swallowing the parasite after touching a surface (such as a doorknob or toy) contaminated with tiny amounts of infected feces.
- Having sex, especially anal sex, with an infected person.
Who gets giardiasis?
Anyone can get giardiasis. Being around places where feces can easily spread (such as centers that care for many small children) can increase your chances of getting infected. People often contract giardiasis after drinking from a river or stream while camping or hiking. This is why giardiasis is sometimes called beaver fever.
Can animals get giardiasis?
Animals can get giardiasis and spread it to other animals. But the Giardia parasite that makes humans sick isn’t the same one that affects animals. So you’re unlikely to get giardiasis from your pet or a wild animal.
What does giardiasis do?
When the Giardia parasite gets inside your body, it lives inside your small intestine. It may make your stomach hurt. Not everyone who comes into contact with Giardia gets sick. If you do get sick, the infection may go away on its own.
What are the symptoms of giardiasis?
Giardiasis usually causes digestive symptoms, such as diarrhea or stomach cramps. Symptoms may be mildly irritating or severe. Some people have no symptoms.
Giardiasis symptoms include:
- Diarrhea (watery or greasy stools).
- Fatigue (feeling overly tired for a long time).
- Unsettled stomach or nausea.
- Stomach cramps.
- Bloating or gas.
- Dehydration, which may cause you to lose weight.
When do giardiasis symptoms start?
If you have giardiasis, you may get sick several days after being infected. Digestive symptoms may last anywhere from two to six weeks.
Symptoms may show up to three weeks after you were first exposed. It’s possible to have no symptoms at all from giardiasis.
Diagnosis and Tests
How is giardiasis diagnosed?
Healthcare providers can diagnose giardiasis by testing your stool for the Giardia parasite. The parasite may not show up in every stool sample. For that reason, your provider may need more than one sample to confirm a diagnosis.
If you have severe symptoms, your provider may examine your intestines using a thin, flexible tube. This procedure is called an upper endoscopy. The parasites are often seen when the tiny pieces of biopsies obtained at the time of endoscopy are stained with lab. Your provider may also take a sample of the contents of your intestine to look for parasites.
Management and Treatment
How is giardiasis treated?
Many people with giardiasis have minor symptoms that go away on their own. You may not need treatment.
If you have more severe parasite symptoms, your provider may prescribe an antibiotic with antiparasitic effect to kill the parasite. Giardia medications include:
- Metronidazole (Flagyl®).
- Tinidazole (Tindamax®).
- Nitazoxanide (Alinia®).
It is important to follow your provider’s instructions and take every pill as prescribed. If not, you may not clear the infection and may need a second course of medication to get rid of the parasite completely. Rarely, some patients develop prolonged or recurrent infection that would need evaluation for disorders of immune system and the help of an infectious disease specialist to formulate the drug combination that could help clear infection.
Can giardiasis be prevented?
Giardia parasites are microscopic (too tiny to see without a microscope). It’s hard to avoid something you can’t see. But there are several ways you can minimize your risk of getting giardiasis.
Wash your hands often.
Wash your hands often with soap and clean, running water for at least 20 seconds. Always wash your hands:
- Before and after you eat.
- After using the toilet.
- After coming in contact with your own or someone else’s germs (such as changing a diaper).
Only drink from safe water sources.
Water can contain parasites, even if it looks clean. Do not drink untreated water, such as from wells, pools, lakes or rivers. If you have any concern about water contamination, don’t drink it. When in doubt, choose bottled water if it’s available. Or boil water for five minutes to kill any parasites.
Know the basics of food safety.
Washing all fruits and vegetables under hot water can prevent giardiasis. Do not eat raw or undercooked meat. Be especially cautious in countries where the water and food may be contaminated.
Practice safe sex.
Practicing safe sex can prevent a wide range of sexually transmitted diseases. To prevent giardiasis, use protection during oral-anal sex, and wash your hands right after sex. These practices can ensure you don’t come into contact with infected feces.
Outlook / Prognosis
What is the prognosis (outlook) for people with giardiasis?
Most people with giardiasis fully recover within two months after having mild to moderate digestive symptoms. Some people continue to have gastrointestinal symptoms (such as lactose intolerance or irritable bowel syndrome) long after the infection is gone.
When should I call my healthcare provider?
Dehydration from diarrhea can be serious. It’s especially dangerous for babies and women during pregnancy. Call your healthcare provider if you notice any symptoms that concern you. For a baby, having fewer wet diapers than usual can be a sign of dehydration.
A note from Cleveland Clinic
Giardiasis can cause minor to severe digestive symptoms, such as loose, runny stools and stomach cramps. The Giardia parasite can live outside the body for a long time. It can survive in water or food and on surfaces such as doorknobs. You can get giardiasis by drinking untreated water, eating contaminated food or having contact with infected feces. Prevent giardiasis by washing your hands regularly and not drinking water that may be unsafe. If you have giardiasis, your healthcare provider may prescribe antibiotics to treat the infection.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy