giardia cyst

Giardia cysts are resistant to chlorine, at least in the amounts usually used for disinfecting water supplies.

In many wilderness areas, such as the Sierra Nevada mountains, water taken from streams has fewer giardia cysts than municipal tap water.

Boiling water for 10 minutes or filtering it can effectively cleanse it of giardia cysts, but they are tough, surviving for more than two months in water at 46 degrees and about one month in 70-degree water.

Once giardia cysts are swallowed, acids in the stomach and enzymes from the pancreas cause them to burst open and release the parasitic phase called a trophozoite (trof-uh-ZO-ite), which attaches itself to the lining of the small intestine where digested foods are normally absorbed.