This is an inflammatory, intestinal condition caused by overgrowth of the protozoan Giardia lamblia. The source of infection is usually untreated water contaminated with G. lamblia cysts.

Giardia lamblia is the most common pathogenic parasite in the U.S. and perhaps the world. Infection with this flagellated protozoan can lead to severe and disabling gastrointestinal symptoms.

Unfiltered stream and lake water that is open to contamination by human feces are a common source of infection to campers...