Giardia: Not a Traveler’s Best Friend

Giardiasis is a fairly common infection of the small intestines caused by the organism Giardia intestinalis (also known as Giardia lamblia). Giardia is a protozoan parasite that thrives in the intestinal tract of mammals and that reproduces by forming cysts, which are transmitted from host to host through the feces of an infected person or animal being ingested by another. The cysts are very resistant and can survive for long periods of time in fresh water, such as lakes, streams and reservoirs.

While Giardia is a common issue in backpackers in the United States (it is present ubiquitously in all states), it is also an under-recognized issue in travelers to developing countries where the water supply can be contaminated.

You can acquire Giardia by:

  • Eating contaminated food or drinking contaminated water;
  • Taking in water while swimming in contaminated lakes, ponds, and other fresh water;
  • Ingesting contaminated feces, including via sexual contact.

Infection is only symptomatic 50% of the time, and it may take up to three weeks or longer for symptoms to occur. However, symptoms are often severe when they arise:

  • Diarrhea
  • Gas
  • Greasy stools that float
  • Stomach pain and cramping
  • Nausea
  • Dehydration
  • Weight loss of ~10 pounds

Symptoms may last 2-6 weeks before resolving, or can be longer-lasting. Once diagnosed, treatment is always a good idea. To properly diagnose Giardiasis, a doctor or other licensed health care provider must order a stool test for specific Giardia antigen testing, since regular ova and parasite microscopic exams often miss this organism. But it's important to do the microscopic exam for other ova and parasites as well, since multiple microorganisms are sometimes contributing to symptoms.

The complications of Giardia can be frustrating. Some people find that they are lactose intolerant or have developed irritable bowel syndrome (IBS) after Giardia intestinalis infection.

To avoid Giardia, take the following steps:

  • Practice good hygiene and hand washing
  • Avoid possibly contaminated water
  • Use a UV water purifier, halogenation, or a filtration device small enough for parasites
  • Boil water long enough to kill cysts (one minute, or 3 minutes at elevations of 6500 feet)
  • Avoid contact with feces
  • Avoid uncooked foods while traveling

If you suspect that you do have Giardia, seek medical attention and get a specific stool test, since usual antibiotics for travelers diarrhea (ciprofloxacin or azithromycin) will not cure this infection. If you have more than one type of infecting organism, you may need multiple medications to treat them all.

If you have after-effects of Giardia infection, medical attention may also be of help in remedying persistent symptoms.

And before you travel to developing countries (including Mexico), consider having a professional travel medicine consultation.


  1. Giardia Treatment and Diagnosis (Stanford)
  2. Patient Information: Giardia (Beyond the Basics),
  3. Giardiasis, Mayo Clinic
  4. Giardiasis, Clinical Key
  5. Giardia Infections, Medline Plus
  6. Giardia infection, National Library of Medicine

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