Walking Well: Giardiasis

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The gastroenteritis of giardiasis is characterized by diarrhea, malaise, weakness, cramps, and other symptoms. However only about a third of infected people have symptoms. Usually the symptoms are mild and last only a week, but some cases become severe and chronic.

Diagnosis in the past relied upon history, symptoms, and a laboratory test that examined the stool for presence of cysts that could be missed. Newer immunologic methods are now available that detect antigens in the stool.

Drug treatment is effective and has included quinacrine (Atabrine), which may not be available in the United States now, and metronidazole (Flagyl).

To prevent giardiasis, drink only safe (filtered, boiled, iodinated, or tested) water. Also wash cooking utensils with soap and hot water and pack them away overnight. Since few hikers exclusively drink certified or treated water, the giardiasis incidence can be reduced by observing safe water rules.

Boiling is best considering that all living contaminants are effectively destroyed. Giardia cysts are 100 percent destroyed by heating to 158 degrees F for 10 minutes (and probably even in fewer minutes). Bringing water to a momentary boil is even better. Most filters, several types of which are available from major equipment supply houses, are effective in removing Giardia cysts. They differ in price, longevity, and sturdiness. Iodination is effective but it takes at least 30 minutes and can take up to eight hours for cold water to achieve 100 percent cyst destruction. Iodine also makes the water taste bad. Chlorine preparations are all much less effective than iodine and are not recommended.

While the stomach, which secretes fairly concentrated hydrochloric acid and digestive enzymes, fights against intruders, hikers should not rely on this or on the certainty that high mountain springs will escape contamination by animals or birds.