An ongoing series.

There's more than just fish
swimming in there.

Although beavers are often blamed for contaminating water with Giardia cysts, they probably do not spread them to new areas, but are rather victims downstream of U.S. National Forest campgrounds. Feces of human carriers are washed by rain into streams. Beavers are then infected and then transmit cysts by defecating in or near the water. Beavers in remote areas have a zero infection rate; beavers and muskrats living near campsites and campground have high infection rates, as do humans themselves. Some Giardia infections have been reported in coyotes, deer, elk, cattle, dogs, and cats, but not in horses and sheep.

My first acquaintance with Giardia came when after running the Moscow marathon in 1989, we visited St. Petersburg (at the time it was called Leningrad). CDC advised us to only drink tea and bottled water and brush teeth with Pepsi because more than half of American visitors who did not take these precautions became positive for Giardia because the water supply was insufficiently treated. We avoided the disease. However, I drank suspicious water on my first thru-hike and had severe diarrhea in Damascus. Though the lab test was negative, I received quinacrine as a precaution. That experience convinced me to only drink safe water.

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