The next time you are out in the field enjoying nature, you might be tempted to quench your thirst by drinking from a nearby stream or spring. But beware, there is a relatively new hazard in our outdoors in addition to poison oak, ticks, and the occasional rattlesnake. It is a microscopic flagellated protozoan, Giardia lamblia, a single-celled organism that inhabit the small intestine of many mammals, including humans. Half of the infected humans in the United States are asymptomatic, that is, they carry the parasite, but do not have the symptoms.
Infected individuals excrete cysts in large numbers, often for months or years.
Giardia 's grand plan for its continued existence is to have another unsuspecting mammal ingest cysts when taking a drink of water and so continue to make more cysts ad infinitum. For thirsty outdoor folks, the wisest course is prevention. Don't drink untreated water in the woods, no matter how clear, cold and free-running the water is. Although the parasite can be killed by drugs, the cure is unpleasant. The drugs cause adverse side effects.