Giardiasis is an infection. It's caused by a parasite called Giardia. It causes diarrhea. It's passed on through oral contact with infected feces. You can get the parasite by eating food or drinking water that contains infected feces. When you hike or travel, make sure not to drink water that may be unsafe. Giardiasis can also be passed from fecal contact during sex. Men who have sex with men are at increased risk of the infection from sex.

Giardiasis a common intestinal parasite. It's most common in countries with poor sanitary conditions, poor water quality control, and overcrowding. But it's 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, and men who have sex with men are more likely to acquire it if their partners have or recently had giardiasis.

The parasite that causes giardiasis lives in two stages:

• Trophozoites. This is the active form inside the body.
• Cysts. This is the resting stage that allows the parasite to survive outside the body.

Infection starts when the cysts are taken in through contaminated food or water. Stomach acid activates the cysts and the trophozoites are released. They attach to the lining of the small intestine and reproduce. Cysts form in the lower intestines. They 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.

Symptoms of giardiasis may include:

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

The time between infection and the start of symptoms is usually 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. See a doctor for diagnosis.

Diagnosis of giardiasis is made by testing stool samples in a lab. Several stool samples may be needed at different times. If you think you may have this illness, talk with your doctor for advice.

Giardiasis may be treated with prescription antibiotic medicines.

Treatment will depend on your symptoms, age, and general health. It will also depend on how severe the condition is.

Several medicines can be used to treat the infection. These include metronidazole, tinidazole, nitazoxanide, and paromomycin.

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

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

• Drink only boiled water or bottled water or drinks.
• Wash your hands thoroughly with soap and water at least 3 times a day and every time after you use the toilet or before you prepare food.
• Don't brush your teeth or wash dishes in water that has not been boiled.
• Don't drink beverages or use ice made from tap water.
• Don't eat locally grown uncooked or unpeeled fruits and vegetables.

Contact your doctor 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

• Giardiasis is an infection. It is caused by a parasite called Giardia. It causes diarrhea.
• Symptoms include explosive, watery, greasy, and foul-smelling stools. You may also have bloating, nausea, pain, gas, fatigue, and loss of appetite.
• You can get the parasite by eating food or drinking water that contains infected feces.
• Several medicines are available that cure the infection.
• Prevention includes good personal hygiene. Wash your hands often with soap and water. Don't consume water, fruits, and vegetables that may have the parasite.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your healthcare doctor if you have questions.