Giardia lamblia in the Sierra Nevada: A New Look
By Alayne Meeks
About the time that large numbers of people were entering the Sierra Nevada for recreation, another traveler was being identified. Giardia lamblia was quickly becoming an unwelcome companion, responsible for a surge in the purchase of water filters and bottled water. This parasite had so infiltrated the mind as well as the water, that no one felt safe from its potential to give us "mild to moderate abdominal discomfort, abdominal distention due to increased intestinal gas, sulfurous or 'rotten egg' burps, highly offensive flatulence, and mild to moderate diarrhea." Sounds like a fellow vacationer well worth avoiding.
In my research for this article, all discussions of Giardia point to one very well researched article written by Robert L. Rockwell entitled, "Giardia lamblia and Giardiasis with Particular Attention to the Sierra Nevada." Rockwell is an active mountaineer and scientist who has been climbing Mt. Whitney each year since 1952. In the course of making over a thousand ascents of hundreds of individual Sierra Nevada mountains, he has never filtered or otherwise treated the water and he has never contracted symptoms of giardiasis.
Rockwell's stance throughout his article is that personal hygiene, or lack thereof, may be more the culprit for abdominal issues than Giardia. "Given the casual approach to personal hygiene that characterizes most backpacking treks, hand washing is likely to be a much more useful preventative strategy than water disinfection." Rockwell quotes Dr. James A. Wilkerson, an expert in wilderness medicine :, "In recent years, frantic alarms about the perils of giardiasis have aroused exaggerated concern about this infestation. Government agencies, particularly the United States Park Service and the National Forest Service, have filtered hundreds of gallons of water from wilderness streams, found one or two organisms [per liter], far less than enough to be infective." Robert W. Derlet, MD and James Carlson, PhD of the UCD School of Medicine agree with Rockwell "that the seriousness of exposure in the wilderness to Giardia has been overemphasized and that bacteria, and not protozoa such as Giardia, pose a greater risk of causing water-borne disease in humans."
As further proof of Rockwell's assertions to the purity of the Sierra waters there is this paragraph to ponder: "Municipal water utilities must use filters to remove the organism. San Francisco water, coming primarily from the Hetch Hetchy watershed in Yosemite National Park, has repeatedly tested positive for Giardia, although at very low levels: typically 0.12 cysts per liter. [A liter being the size of the average water bottle carried by hikers] While it theoretically takes only 1 cyst to get the disease, "studies have shown that it takes 10 or greater cysts to have a reasonable probability of contracting giardiasis." This water is of such high quality that the US Environmental Protection Agency and the California Department of Health Services have granted Hetch Hetchy water a filtration exemption, meaning that filtration treatment to ensure its safety from Giardia and other organisms is not required. The Los Angeles Aqueduct, which transports water to that city from the eastern slopes of the Sierra Nevada, averages 0.03 cysts per liter."
Rockwell continues his thoughts on Giardia: "Because up to 1 in 14 of us carries the Giardia parasite, we all need to do what we can to keep the water pure. Defecate away from water and bury it, or carry it out. Camp cooks in particular need to pay special attention to cleanliness. Wash hands thoroughly, especially before handling utensils and preparing meals. If you contract giardiasis in the backcountry, blame your friends...not the water. High Sierra water has far too few Giardia cysts for you to contract and infestation from it. Even if you go somewhere where the concentration is high, you probably won't get giardiasis. If you do get giardiasis, you probably won't have any symptoms. If you have symptoms, they will probably go away by themselves in a week or so. If they don't or you develop serious persistent symptoms, you should seek medical treatment. Finally those contracting giardiasis may develop immunity to it, thus lowering the likelihood that they will get it again. There is certainly no reason for anxiety about giardiasis. Fewer than 1 percent of those who have an infestation, or about 5 percent of those with symptoms, need medical help."
Rockwell offers these observations on Sierra Nevada waters: "few Giardia cysts survive harsh high Sierra winters, contamination begins essentially anew each year, so springtime water is safer than summer or fall;" water at higher elevations is safer than lower, partly because of reduced human and animal presence up high, and partly because water flowing to lower elevations picks up more contaminants the more distance it travels;" "the colder the water is, the more likely it is freshly melted, meaning less opportunity for contamination;" "because filtration of water through soil removes Giardia cysts, deep well water is considered safe, by implication springs in the wilderness should be too;" "avoid water that likely could have passed through an area subject to heavy human or animal use;" if it doesn't look good -it's cloudy or has surface foam - treat it or don't drink it."
So I think I might try drinking from Fern Spring once again and not worry so much about those drops of water that splash my face as I now swim more easily in the waters of the Sierras.
For more information refer to Rockwell's article at http://lomaprieta.sierraclub.org/pcs/articles/giardia.asp and the UCD piece at www.sierranevadawild.net/Learn/coliform.htm. My thanks also go to Nick Gravem of the Down Works for bringing this issue to my attention
| Concentration | Effects and Sources |
|---|---|
| ~1000 | Typical swimming pool contamination |
| ~100 | Giardiasis is plausible | ~10 | Minimum needed to contract giardiasis |
| ~1 | Some wilderness water outside California |
| 0.12 | Some San Francisco water |
| 0.108 | Worst Sierra Nevada water |
| 0.030 | Some Los Angeles Aqueduct water |
| 0.013 | Mt. Whitney at Trail Camp |
| 0.003 | Mt. Whitney at Whitney Portal |
~ means approximate
Editor's note: Before drinking any untreated water, educate yourself on the potential risks by reading the original references listed above. The Center for Disease Control (www.cdc.gov) is also a good source for information.