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The Informed Parent

Water Parasite

by John H. Samson, M.D., F.A.A.P.
Published on Sep. 18, 2000
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Upon returning from a camping trip in the eastern Sierras a patient brought up a question pertaining to a parasite that lives in the streams and causes bowel disease. None of his family was sick, but he wanted to know more about the problem in order to protect his family in the future.

The parasite in question is called Giardia lamblia. It lives in the beautiful, ice cold, crystal-clear streams of that area in California. This parasite has worldwide distribution and is transmitted by drinking contaminated water, or from person-to-person contact. The principal reservoir is the human. Obviously one can contract this problem without mounting an expedition into the Sierra wilderness. The existence of the parasites in remote mountain water suggests animals also play a role as a source of these organisms.

The Giardia parasite exists in three forms during its life cycle. The trophozoite and mature flagellate are very fragile, and can live for only a few hours outside the body. The cystic form is the infective stage, which can live for several days outside the intestinal tract of the host.

The cyst is ingested. It ruptures and the parasite sets up housekeeping in the first half of the small bowel. They may live there for years, or leave spontaneously in a short time. It is felt that symptoms are noted when there are a large number of parasites present. The symptoms of Giardiasis are diarrhea, cramps, loss of appetite and in severe cases weight loss due to the inability of the bowel to properly absorb food. The diarrhea tends to be persistent, frequent and unresponsive to the usual forms of therapy for this symptom.

Since it is a parasite, culturing the stool for bacteria yields no growth. The stool must be examined for evidence of the parasite. This test is referred to as a "stool for O & P", ova and parasite. Because the parasite is shed intermittently, the best chance of recovering it in the stool is by doing a series of three tests on alternate days. Also, if these tests are negative a special string test can be done, which increases the chance of finding the parasite.

The specific treatment is usually effective. There are several agents that can be used. Your physician will select the one he feels is most effective.

The most important aspect of the problem is prevention. To accomplish this, do not drink untreated stream water, no matter how inviting it is. It’s hard to believe that a fresh, cold, cascading mountain stream could harbor an unwanted parasite. Believe me, it can and usually does. This water can be used if it is boiled for five minutes or put through a water purification filter that traps the cysts. You can purchase such a filter at most camping supply stores. Chlorine in usual concentrations does not eradicate the parasite.

Once again, the best treatment is prevention. If you treat the water you can have a ready source of safe, clear, mountain stream water.




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