| What it is | Waterborne intestinal parasite |
| Illness | Diarrhea, gas, cramps, nausea |
| Onset | ~1–3 weeks after infection |
| Prevent with | Filter/boil/chemically treat water; hygiene |
Giardia (Giardia lamblia) is a microscopic parasite found in many backcountry water sources that causes giardiasis, an intestinal illness with diarrhea, gas, cramps, and nausea appearing one to three weeks after infection. It’s a leading reason to treat all wild water, and is prevented by filtering, boiling, or chemically treating water and by good hand hygiene.
This is general educational information, not medical advice. See a clinician if you suspect giardiasis.
Prevention
Treat every water source — a filter, boiling, or chemicals all stop Giardia (see water treatment). Proper waste disposal (WAG bag or cat-hole) protects water for others.
Frequently asked questions
What is Giardia?
Giardia is a microscopic protozoan parasite that lives in the intestines of humans and animals and is shed in feces, contaminating water sources. Swallowing even a few cysts from untreated backcountry water can cause giardiasis, a common and unpleasant gastrointestinal infection sometimes called 'beaver fever.'
What are the symptoms of giardiasis?
Giardiasis typically causes diarrhea, greasy or foul-smelling stools, abdominal cramps, bloating and gas, nausea, and fatigue, often with weight loss. Symptoms usually start one to three weeks after exposure and can last weeks; some people have no symptoms but still spread it. It's diagnosed by stool testing and treated with prescription medication.
How do you prevent Giardia infection?
Treat all backcountry water before drinking — most water filters remove Giardia, as do boiling and chemical treatments like chlorine dioxide (allow extra contact time for cysts). Practice good hygiene: wash or sanitize hands after using the bathroom and before handling food, and bury or pack out human waste away from water to protect sources for others.
Sources
- Giardia & giardiasis — CDC
- Backcountry water safety — National Park Service