Giardia Article

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" rowspan="2" width=139 style="border-right: 1px solid #AAAAAA;" BGCOLOR="#808080" TEXT="#080000" bgproperties="fixed" background="b1216c00eowhpc.jpg"> <bR> <div> <A HREF="index.htm" TARGET="_top" TITLE="Sierra Spirit Discover the Soul of the "><B>Home</B></A></div> <div> <A HREF="sierra_spirit_philosophy.htm" TARGET="_top" TITLE="Sierra Spirit Philosophy"><B>Backpacking</B></A></div> <div> <A HREF="id3.htm" TARGET="_top" TITLE="Serene Lakes Cabin Rental"><B>Serene Lakes Cabin Rental</B></A></div> <bR> <bR> <bR> </td> <td valign="top" height=140 BGCOLOR="#DDDDDD" TEXT="#080000"> <div> <B><IMG SRC="b147e690.jpg" border=0 width="894" height="105" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></div> <div> <TABLE BORDER="2" CELLPADDING="0" CELLSPACING="1" WIDTH="897" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#777777" FRAME="BOX" RULES="ALL" ALIGN="LEFT" HSPACE="0" VSPACE="0" BGCOLOR=#FFFFFF > <tR> <tD VALIGN=CENTER HEIGHT= 25 WIDTH="56"><div> <A HREF="index.htm" TARGET="_top" TITLE="Sierra Spirit Discover the Soul of the "><FONT COLOR="#000000"><B>Home</B></FONT></A></div> </tD> <tD VALIGN=CENTER><NOBR><div> <A HREF="sierra_spirit_philosophy.htm" TARGET="_top" TITLE="Sierra Spirit Philosophy"><FONT COLOR="#000000"><B>Philosophy</B></FONT></A></div> </NOBR></tD> <tD VALIGN=CENTER WIDTH="56"><div> <A HREF="2014_bkpking.htm" TARGET="_top" TITLE="2014 Backpacking"><FONT COLOR="#000000"><B>Trips</B></FONT></A></div> </tD> <tD VALIGN=CENTER WIDTH="56"><div> <A HREF="id4.htm" TARGET="_top" TITLE="Your Guides"><FONT COLOR="#000000"><B>Guides</B></FONT></A></div> </tD> <tD VALIGN=CENTER><NOBR><div> <A HREF="about_sierra_spirit.htm" TARGET="_top" TITLE="About Sierra Spirit"><FONT COLOR="#000000"><B>About Sierra Spirit</B></FONT></A></div> </NOBR></tD> <tD VALIGN=CENTER><NOBR><div> <A HREF="id22.htm" TARGET="_top" TITLE=" Free Slide Shows"><FONT COLOR="#000000"><B>Free Slide Shows</B></FONT></A></div> </NOBR></tD> <tD VALIGN=CENTER><NOBR><div> <A HREF="client_info.htm" TARGET="_top" TITLE="Client Info"><FONT COLOR="#000000"><B>Client Info.</B></FONT></A></div> </NOBR></tD> <tD VALIGN=CENTER WIDTH="54"><div> <A HREF="faqs.htm" TARGET="_top" TITLE="FAQs"><FONT COLOR="#000000"><B>FAQ's</B></FONT></A></div> </tD> <tD VALIGN=CENTER><NOBR><div> <A HREF="id123.htm" TARGET="_top" TITLE="Testimonials from Clients:"><FONT COLOR="#000000"><B>Testamonials</B></FONT></A></div> </NOBR></tD> <tD VALIGN=CENTER WIDTH="44"><div> <A HREF="blog.htm" TARGET="_top" TITLE="Blog"><FONT COLOR="#000000"><B>Blog</B></FONT></A></div> </tD> <tD VALIGN=CENTER WIDTH="70"><div> <A HREF="contact.htm" TARGET="_top" TITLE="Contact"><FONT COLOR="#000000"><B>Contact</B></FONT></A></div> </tD> </tR> </TABLE></div> <bR> <bR> <div> </div> </td> <td valign="top" rowspan="2" width=0 style="border-right: 2px solid #AAAAAA;" BGCOLOR="#99CC99" TEXT="#080000" bgproperties="fixed" background="03e8dfc3.jpg"> <bR> </td> </tr><tr> <td valign="top" height=340 width="100%" BGCOLOR="#DDDDDD" TEXT="#080000"> <bR> <div> <B>Giardia Article</B></div> <bR> <bR> <bR> <div> <B> <TABLE BORDER="2" CELLPADDING="20" CELLSPACING="1" WIDTH="885" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="BOX" RULES="ALL" HSPACE="0" VSPACE="0" BGCOLOR=#BBBBBB > <tR> <tD VALIGN=TOP BGCOLOR=#BBBBBB HEIGHT= 7633 ><NOBR><bR> <div> <TABLE BORDER="2" CELLPADDING="15" CELLSPACING="1" WIDTH="836" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="BOX" RULES="ALL" HSPACE="0" VSPACE="0" BGCOLOR=#EEEEEE > <tR> <tD VALIGN=TOP BGCOLOR=#FFFFFF HEIGHT= 7560 ><NOBR><div> <B>12 May 2002</B></div> <div> <I><B>Giardia Lamblia </B></I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Bold" ><B>and Giardiasis</B></FONT></div> <div> <B>With Particular Attention to the Sierra Nevada</B></div> <div> <B>By Robert L. Rockwell</B></div> <bR> <bR> <div> Figure 1. <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia lamblia </I></FONT>trophozoites as they appear with the scanning electron microscope.*</div> <bR> <div> Ask the average outdoors person about <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia lamblia </I></FONT>or giardiasis, and they have certainly heard</div> <div> about it. Almost always, however, they are considerably misinformed about both the organism?s</div> <div> prevalence in wilderness water, and the seriousness of the disease if contracted.</div> <div> With the advent of the Internet, the amount of information one can easily find on the subject is</div> <div> voluminous. Unfortunately, most of it is flawed in important aspects, being unsubstantiated, anecdotal,</div> <div> or merely quoting other unsubstantiated and anecdotal articles. Official sources, such as many</div> <div> informational publications put out by the US government, are not immune to this criticism.</div> <div> This paper is the result of a critical distillation of relevant articles, retaining only those from</div> <div> scholarly, peer-reviewed, or otherwise professional and trustworthy sources.</div> <div> One conclusion of this paper is that you can indeed contract giardiasis on visits to the Sierra Nevada,</div> <div> but it almost certainly won?t be from the water. So drink freely and confidently: Proper personal</div> <div> hygiene is far more important in avoiding giardiasis than treating the water.</div> <div> First, an excerpt written by a highly regarded wilderness physician:</div> <div> <I>?In recent years, frantic alarms about the perils of giardiasis have aroused exaggerated</I></div> <div> <I>concern about this infestation. Government agencies, particularly the United States Park</I></div> <div> <I>Service and the National Forest Service, have filtered hundreds of gallons of water from</I></div> <div> <I>wilderness streams, found one or two organisms (far less than enough to be infective),</I></div> <div> <I>and erected garish signs proclaiming the water ?hazardous.??1</I></div> <div> * Original image by Arturo Gonzalez, CINVESTAV, Mexico. From http://www.biosci.ohiostate.</div> <div> edu/~parasite/giardia_sem.html</div> <div> And another, by researchers who surveyed the health departments in all 50 states and scanned the</div> <div> medical literature looking for evidence that giardiasis is a significant threat to outdoor folk:</div> <div> <I>?Neither health department surveillance nor the medical literature supports the widely</I></div> <div> <I>held perception that giardiasis is a significant risk to backpackers in the United States.</I></div> <div> <I>In some respects, this situation resembles (the threat to beachgoers of a) shark attack:</I></div> <div> <I>an extraordinarily rare event to which the public and press have seemingly devoted</I></div> <div> <I>inappropriate attention.?2</I></div> <div> I explored this subject in 19873 and again in 19964 with an update in 1997.5 The conclusions have</div> <div> always been that the ?<FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>problem? in Sierra Nevada water is grossly exaggerated, and that the</div> <div> cases of giardiasis subsequent to wilderness visits are wrongly blamed on the water. After incorporating</div> <div> the recent information for this paper, those prior conclusions are not only still valid but also</div> <div> considerably reinforced.</div> <div> <B>Just who is this little guy, anyway? </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >6, 7, 8, 9, 10</FONT></div> <div> <I>Giardia lamblia</I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >, now also known as </FONT><I>G. intestinalis </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >or </FONT><I>G. duodenalis</I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >, was first observed in 1681 by</FONT></div> <div> Anton van Leeuwenhoek, inventor of the microscope. The parasite was named in 1915 for two</div> <div> scientists who studied it: Prof. A. Giard in Paris and Dr. F. Lambl in Prague.</div> <div> <I>Giardia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >is a flagellated (having whip-like appendages for locomotion) protozoan that, in the</FONT></div> <div> trophozoite (active) form, attaches itself with an adhesive disk to the lining of the upper intestinal tract</div> <div> of the host animal. There, it feeds and reproduces. Trophozoites divide by binary fission about every</div> <div> 12 hours. Thus, a single parasite can theoretically result in more than a million in 10 days and a billion</div> <div> in 15 days.</div> <div> At some time in its active life, the trophozoite releases its hold on the bowel wall and floats in the</div> <div> fecal stream. As it makes its journey, it transforms into an egg-like structure called a cyst, which is</div> <div> eventually passed in the stool. Duration of cyst excretion, called shedding, may persist for months.</div> <div> Once outside the body, the cysts can be ingested by another animal. Then, they ?hatch? into</div> <div> trophozoites due to stomach acid action and digestive enzymes, and the cycle repeats.</div> <div> The trophozoite is 9 - 15 <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >µ</FONT>m long, 5 - 15 <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >µ</FONT>m wide, and 2 - 4 <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >µ</FONT>m thick. Unlike the cyst, it cannot live</div> <div> for long outside a host. Cysts are 8 - 12 <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >µ</FONT>m long by 6 - 9 <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >µ</FONT>m in diameter; so a million could fit under a</div> <div> fingernail. Cysts can survive for as long as 2 to 3 months in cold water,10, 11 but they cannot tolerate</div> <div> drying12 or freezing.9, 12, 13, 14</div> <div> A significant infestation can leave millions of trophozoites stuck tight to the intestinal lining. There,</div> <div> they cripple the gut?s ability to secrete enzymes and absorb food, especially fats, thereby producing the</div> <div> disease?s symptoms. The symptoms typically appear one to two weeks after ingestion, with an average</div> <div> of nine days, but four weeks is not uncommon. Symptoms can vanish suddenly and then reappear.</div> <div> They may hide for months. They may not appear at all.10, 15</div> <div> There are three ways that giardiasis, the disease caused by ingesting <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts, can be</div> <div> contracted: contaminated water, contaminated food, and direct fecal-oral. A person who has just come</div> <div> down with the disease and who wishes to identify the source needs to reflect on not only the possibility</div> <div> of each of these avenues, but in a suspect period ranging from typically one week to four weeks earlier.</div> <div> <B>The bad news: </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,BoldItalic" ><I><B>Giardia lamblia </B></I></FONT><B>is almost everywhere </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >1, 6, 7, 8, 9, 10, 16, 17, 18, 19, 20, 21</FONT></div> <div> Giardiasis has been most often associated with travel to such places as Latin America, Africa, Asia,</div> <div> and the former Soviet Union. However, <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>has always been present in wilderness streams, in the</div> <div> water supplies of most cities around the world, and even in the municipal water of large US cities. In</div> <div> fact, in the 1930s and 1940s, before regulated municipal water treatment plants, everyone was drinking</div> <div> <I>Giardia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >all the time.22</FONT></div> <bR> <div> Currently, <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia lamblia </I></FONT>is the most commonly diagnosed intestinal parasite in North America.24</div> <div> It is the most frequently identified cause of diarrheal outbreaks associated with drinking water in this</div> <div> country. Fully 20 percent of the world?s population is infected, and up to 7 percent of Americans, most</div> <div> without any symptoms at all.10, 23 The Centers for Disease Control and Prevention (CDC) estimates that</div> <div> as many as 2,500,000 cases occur annually in the US or about one for every 100 persons.24</div> <div> Infestation rates of 60 percent of the children in day care centers across the country have been noted.</div> <div> Institutions for mentally retarded persons can have high rates. Other high-rate populations include</div> <div> promiscuous male homosexuals, international travelers, and patients with cystic fibrosis. And family</div> <div> members of these individuals.</div> <div> In an incident in New Jersey a child had a ?fecal accident? in a 700,000-liter swimming pool, and</div> <div> nine swimmers came down with the disease.25 How many <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts might have been involved?</div> <div> The number of cysts shed in feces is highly variable but has been estimated as high as 900 million per</div> <div> day for a human.</div> <div> Municipal water utilities must use filters to remove the organism. San Francisco water, coming</div> <div> primarily from the Hetch Hetchy watershed in Yosemite National Park, tests positive for <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>about</div> <div> 23 percent of the time, although at very low levels: fewer than 0.12 cysts per liter?. This water is of</div> <div> such high quality that the US Environmental Protection Agency and the California Department of</div> <div> Health Services have granted Hetch Hetchy water a filtration exemption, meaning that filtration</div> <div> treatment to ensure its safety from <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>and other organisms is not required.26 The Los Angeles</div> <div> Aqueduct, which transports water to that city from the eastern slopes of the Sierra Nevada, averages</div> <div> 0.03 cysts per liter before treatment.27</div> <div> Drinking highly contaminated water is one way to get the disease. Less common in developed</div> <div> countries is direct passage from stool to the hands of a food preparer and then to the food itself. When</div> <div> 16 people got sick from the salad at a Connecticut picnic, the CDC tracked the source to a woman who</div> <div> had mixed the salad with her hands. She didn?t have giardiasis, but one of her children did?without</div> <div> any symptoms.15 A similar situation occurred in New Jersey, with the salad preparer testing positive for</div> <div> <I>Giardia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >along with her child and pet rabbit.28</FONT></div> <div> Contaminated food may be a less-common source for the general population, but for wilderness</div> <div> visitors, it may be the most important one. Put another way: If the water is clean, food-borne and direct</div> <div> fecal-oral routes are the only pathways.</div> <div> On a recent climbing expedition to Tibet, members of our party came down again and again with</div> <div> what was undoubtedly giardiasis. Our water came from glacial melt, but all our food in advanced base</div> <div> camp and below was prepared by Sherpa cooks. Much of the food they prepared?potatoes, rice,</div> <div> cauliflower, cabbage, onions?came from Nepal. We were continually assured that the cooks were</div> <div> practicing good hygiene, yet we had major intestinal problems that prevented many of the participants</div> <div> from getting high on the mountain.</div> <div> The disease has been referred to as ?beaver fever? because of a presumed link to those waterdwelling</div> <div> animals known to be carriers. However, it has been suggested that it is more likely that</div> <div> humans have carried the parasite into the wilderness and that beavers may actually be the victims. In</div> <div> particular, there is a growing amount of data showing that beavers living downstream from</div> <div> campgrounds have a high <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>infection rate compared with a near-zero rate for beavers living in</div> <div> more remote areas.</div> <div> In any case, beavers can and do contract giardiasis. Being water-dwellers, they are thus able to</div> <div> contaminate water more directly than an animal that defecates on the ground.</div> <div> ? The referenced sources use a variety of units for portraying cyst concentration: cysts per 100 liters, per</div> <div> 100 gallons, etc. For uniformity, all have been converted to cysts per liter since that is the size of the</div> <div> typical backpacker?s canteen.</div> <bR> <bR> <div> Other animals that can harbor <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>are bighorn sheep, cats, cattle, coyotes, deer, dogs, elk,</div> <div> muskrats, pet rabbits, raccoons, and squirrels. But naturally occurring infections have not been found in</div> <div> most wild animals including badgers, bears, bobcats, ferrets, lynxes, marmots, moose, porcupines,</div> <div> rabbits, and skunks. In the past, horses and domestic sheep were thought to be <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia</I></FONT>-free, but more</div> <div> recent studies have shown that they can sometimes be infected.12, 29 Indeed, in some cases the issue</div> <div> seems to one of degree and not a black-or-white situation.</div> <div> If ?It?s everywhere!? why is it not <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>more </I></FONT>of a problem?</div> <div> <B>The good news: Most of the time, the concentration of </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,BoldItalic" ><I><B>Giardia </B></I></FONT><B>cysts is very low </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >1, 6, 8</FONT></div> <div> Outside of places where fecal accidents occur, dirty diapers congregate, and cities where water</div> <div> treatment plants break down or are ineffective, there is little room to worry. A few <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts now</div> <div> and then will cause no harm, and in fact may be useful in developing an immunity as will be expanded</div> <div> upon later.</div> <div> How many cysts does it take to get the disease? Theoretically only one, but volunteer studies have</div> <div> shown that 10 or so are required to have a reasonable probability of contracting giardiasis: About onethird</div> <div> of persons ingesting 10 ? 25 cysts get detectable cysts in their stools. 6, 7, 8, 10, 30, 31</div> <div> But be careful with statistics: Animal droppings containing 100,000 <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts deposited at the</div> <div> edge of a 10 million liter lake may be an average of only 0.01 per liter for the lake as a whole, but in the</div> <div> immediate vicinity of the deposit, the concentration can be much higher.</div> <div> A comforting observation is that significant cyst inactivation, as high as 99.9 percent, can occur as a</div> <div> result of anaerobic digestion in sewage sludge.32 Of course, using a simple cat hole is not exactly a</div> <div> good approximation to the sewage plant process, but this points out the wisdom of doing something</div> <div> better than just leaving it on the ground or under a couple of rocks. On the other hand, cysts perish in a</div> <div> day on dry surfaces,12 so smearing it over a rock slab makes some sense when burial is not feasible.</div> <div> Since cysts that ?winter over? in the Sierra Nevada are either in liquid water for considerably more</div> <div> than 2 to 3 months, or exposed to freezing temperatures, it would appear that few will survive the harsh</div> <div> Sierra winters. So, except for pollution by winter mountaineers and non-hibernating animals, <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia</I></FONT></div> <div> contamination in the high country must begin essentially anew each spring.</div> <div> <B>More good news: If you have a </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,BoldItalic" ><I><B>Giardia </B></I></FONT><B>infestation, you will likely have no symptoms </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >1, 6, 7, 17, 18, 33,</FONT></div> <div> 34</div> <div> The symptoms of giardiasis vary widely. Characteristic symptoms, when they occur, are mild to</div> <div> moderate abdominal discomfort, abdominal distention due to increased intestinal gas, sulfurous or</div> <div> ?rotten egg? burps, highly offensive flatulence, and mild to moderate diarrhea. Stools are soft (but not</div> <div> liquid), bulky, and foul smelling. They have been described as greasy and frothy, and they float on the</div> <div> surface of water. Nausea, weakness, and loss of appetite may occur. Studies have shown that giardiasis</div> <div> can be suspected when the illness lasts seven or more days with at least two of the above symptoms.7</div> <div> However, most infected individuals have no symptoms at all! In one incident1 studied by the CDC,</div> <div> disruption in a major city?s water disinfection system allowed the entire population to consume water</div> <div> heavily contaminated with <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia</I></FONT>. Yet only 11 percent of the exposed population developed</div> <div> symptoms even though 46 percent had organisms in their stools. These figures suggest that (a) even</div> <div> when ingesting large amounts of the parasite, the chance of contracting giardiasis is less than 1 in 2, and</div> <div> (b) if you are one of the unlucky ones to contract it, the chance of having symptoms is less than 1 in 4.</div> <div> But perhaps the most telling statistic is that drinking <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>heavily contaminated </I></FONT>water resulted in symptoms</div> <div> of giardiasis in only 1 case in 9.</div> <div> <B>If you have symptoms it may not be giardiasis </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >1, 7, 15, 18, 35</FONT></div> <div> Many people claim that they ?got it? on a particular trip into the wilderness. Yet upon questioning,</div> <div> they usually report that the presence of <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>was not confirmed in the laboratory. (Only 8 percent of</div> <bR> <div> persons with a diarrheal illness in this country seek medical care.24) Depending on the situation, more</div> <div> likely offenders are Campylobacter, Cryptosporidium, Salmonella, Shigella, Yersinia, Aeromonas,</div> <div> Clostridium, and Escherichia coli, with the last being the most common cause of traveler?s diarrhea</div> <div> worldwide. Food poisoning is also a possibility.</div> <div> Cryptosporidiosis, in particular, is a growing problem in this country, and currently, there is no</div> <div> effective treatment for it. An outbreak in Milwaukee in 1993 caused 403,000 people to become ill and</div> <div> 100 to die. A year later, 43 people in Las Vegas died from the same disease.36 The severity of</div> <div> cryptosporidiosis depends on the condition of the host?s immune system. In immunologically normal</div> <div> people, symptoms and duration are similar to those of giardiasis. But in persons whose immune systems</div> <div> have been compromised (e.g., AIDS victims), symptoms can be profound: Frequent (6 to 25),</div> <div> voluminous (1 to 25 liters) daily bowel movements, serious weight loss, and cyst shedding often persist</div> <div> for months.</div> <div> The diarrhea being blamed on <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>from that climbing trip a week ago may instead be due to</div> <div> some spoiled food eaten last night or Campylobacter in undercooked chicken four days ago. Or,</div> <div> because the incubation period is usually from one to four weeks, even if it is giardiasis the uncertainty</div> <div> range indicates that the culprits could have been ingested anytime during a full three weeks worth of</div> <div> meals and beverages. People in high-risk groups for <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia</I></FONT>, such as family members of children in day</div> <div> care centers or promiscuous male homosexuals, have even more possible sources to consider. To indict</div> <div> a particular stream or lake under such circumstances, without being able to at least verify that cysts are</div> <div> indeed there at all, is illogical at best.</div> <div> The type of diarrhea can help in the diagnosis: If it is liquid and mixes readily with water rather than</div> <div> floating on top and is not particularly foul smelling, the problem is likely something other than</div> <div> giardiasis. Diarrhea which lasts less than a week, untreated, is probably not from giardiasis.</div> <div> <B>Almost always, giardiasis goes away without treatment </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >1, 6, 7, 15, 16, 17, 33, 37</FONT></div> <div> If you are unlucky enough to get giardiasis with symptoms, the symptoms will probably go away in</div> <div> a week or so without treatment. You may still be harboring the cysts, however, and can unknowingly</div> <div> spread the disease. Thus, practicing commonly recommended wilderness sanitary habits?defecating</div> <div> 100 feet from water, burying or packing out feces and toilet paper, washing before handling food, etc.?</div> <div> is an excellent idea.</div> <div> The US Food and Drug Administration, observing that giardiasis is more prevalent in children than</div> <div> adults, suggests that many individuals seem to have a lasting immunity after infection.38 Furthermore,</div> <div> citizens of cities and countries where the parasite is numerous clearly seem to have few if any problems</div> <div> with their own water, which also points to an acquired immunity. So there is a possible bright side to</div> <div> contracting the disease.</div> <div> Looking for cysts and trophozoites in stool specimens under the microscopic has been the traditional</div> <div> method for diagnosing giardiasis, but it is notoriously unreliable. Now, however, an immunologic test</div> <div> (enzyme-linked immunosorbent assay, or ELISA) for the detection of <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>antigens in stool samples</div> <div> is available. The antigens are present only if there is a <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>infection. ELISA is a big improvement</div> <div> over the microscopic search, with detection sensitivities of 90 percent or more.</div> <div> Rare individuals not only do not spontaneously rid themselves of the organisms but instead develop</div> <div> serious symptoms of malabsorption, weight loss, ulcer-like stomach pain, and other chronic</div> <div> disturbances. Fortunately, this occurs in fewer than 1 percent of those with infestations. These unlucky</div> <div> people need medical treatment.</div> <div> Metronidazole (Flagyl) has been the standard medication, with about a 92 percent cure rate.</div> <div> Recommended by the CDC, it is not approved by the FDA for giardiasis because it can have some</div> <div> serious side effects and is potentially carcinogenic. Quinacrine (Atabrine) and furazolidone (Furoxone)</div> <div> are also prescribed. Tinidazole (Tinebah) is highly effective in single doses and is widely used</div> <bR> <div> throughout the world, but it is not available in the US; it can be purchased over-the-counter in many</div> <div> developing countries.7, 24</div> <div> Giardiasis has been called a disease of ?somes.? Some people do not contract it even from heavily</div> <div> contaminated sources. Some infestations vanish with no treatment at all. Some people become asymptomatic</div> <div> carriers. Some evidence suggests that some people acquire a natural immunity to some strains.</div> <div> And some strains seem more virulent than others.15</div> <div> The problem may not be whether you are infected with the parasite but how harmoniously you both</div> <div> can live together. And how to get rid of the parasite when the harmony does not exist or is lost.6</div> <div> <B>So, what about the Sierra Nevada? </B><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >1, 6, 7, 8, 16, 18</FONT></div> <div> In 1984, the US Geological Survey in cooperation with the California Department of Public Health</div> <div> examined water at 69 Sierra Nevada stream sites that were selected in consultation with Park Service</div> <div> and National Forest managers.39, 40 Forty-two of the stream sites were considered ?high-use? (high</div> <div> probability of human fecal contamination), and 27 were ?low-use.? Cysts were found at only 18 (43</div> <div> percent) of the high-use sites and at 5 (19 percent) of the low-use sites. The highest concentration of</div> <div> <I>Giardia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >cysts was 0.108 per liter of water in Susie Lake, south of Lake Tahoe. The next highest was</FONT></div> <div> 0.037 per liter near Long Lake, southwest of Bishop. Samples taken in the Mt. Whitney area varied</div> <div> from 0 (most sites) to 0.013 (Lone Pine Creek at Trail Camp) per liter. The concentration was 0.003 per</div> <div> liter in Lone Pine Creek at Whitney Portal.</div> <div> Recall that San Francisco water can contain a concentration approaching 0.12 cysts per liter,26 a</div> <div> figure now seen to be higher than that measured anywhere in the Sierra. San Francisco city officials go</div> <div> to great lengths to assure their citizens that the water is safe to drink, and if true?as it most assuredly</div> <div> must be?this comparison alone is quite revealing.</div> <div> Even Los Angeles Aqueduct water, with only 0.03 cysts per liter,27 has a higher concentration of</div> <div> <I>Giardia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >than all but two of the 69 Sierra sites examined.</FONT></div> <div> Taking the highest concentration measured in the Sierra (0.108), we can make some calculations.</div> <div> The probability? of finding 10 or more cysts in a liter of water?to have at least a one-third chance of</div> <div> contracting giardiasis?is about 10-17. Ten cysts in 10 liters of water, about 10-7. In fact, one would</div> <div> have to drink over 89 liters to have a 50 percent probability of ingesting 10 or more cysts.</div> <div> A word of caution: The concentration is never uniform, as suggested by the ?lake incident? above.</div> <div> Another reason for caution: 1984 was quite a while ago, and areas of the Sierra may be differently</div> <div> contaminated now: some perhaps more, some perhaps less. Also, while so much attention is being</div> <div> given to <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia</I></FONT>, there are worse organisms to worry about such as Campylobacter, Cryptosporidium,</div> <div> E. coli, and the others mentioned earlier.</div> <div> In an informative study,41 investigators contacted thousands of visitors to one of the high-use sites</div> <div> during the summers of 1988 through 1990. Water samples taken on 10 different dates at each of three</div> <div> locations exhibited <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cyst concentrations between 0 and 0.062 (average 0.009) per liter. A goal</div> <div> was to enlist volunteers who were cyst-negative before their trip, verified by stool analysis, and then</div> <div> determine what fraction were cyst carriers after the trip. Unfortunately, stool collection is not a</div> <div> particularly enjoyable task, and only 41 people agreed to participate. Of these, two acquired <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia</I></FONT></div> <div> cysts during their trip, but neither came down with symptoms. Six of the others exhibited post-visit</div> <div> intestinal symptoms, but none tested positive for <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>(interestingly, all six had filtered their water).</div> <div> In sum, no cases of laboratory-confirmed symptomatic giardiasis were found.</div> <div> The water that wilderness travelers are apt to drink, assuming that they use a little care, seems</div> <div> almost universally safe as far as <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>is concerned. The study referred to earlier,2 in which the</div> <div> researchers concluded that the risk of contracting giardiasis in the wilderness is similar to that of a shark</div> <div> attack, is telling. What they did find is that <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>and other intestinal bugs are for the most part</div> <div> ? These calculations involve use of a tool called the Poisson distribution.</div> <bR> <bR> <div> spread by direct fecal-oral or food-borne transmission, not by contaminated drinking water. Since</div> <div> personal hygiene often takes a backseat when camping, the possibility of contracting giardiasis from</div> <div> someone in your own party?someone who is asymptomatic, probably?is real. Recalling that up to 7</div> <div> percent of Americans, or 1 in 14, are infected, it is not surprising that wilderness visitors can indeed</div> <div> come home with a case of giardiasis contracted not from the water?but from one of their friends.</div> <div> This theme, that reduced attention to personal hygiene is an important factor for contracting</div> <div> giardiasis in the wilderness, is becoming more frequent in the literature.2, 10, 16, 41, 42</div> <div> Outside of the Sierra, <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts in concentrations ?as high as four per gallon?? have been</div> <div> detected in untreated water in northeastern and western states.43 But even with this concentration, one</div> <div> would have to consume over nine liters of water to have a 50 percent chance of ingesting 10 or more</div> <div> cysts.</div> <div> Indeed, there may be as much unwarranted hysteria surrounding <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>in wilderness water in</div> <div> these other areas as there is for the Sierra. For example, an oft-cited report describing acquisition of the</div> <div> disease by 65 percent of a group of students hiking in the Uinta Mountains of Utah44 is now viewed with</div> <div> considerable skepticism. Specifically, the attack rate was far beyond that usually seen with watercontracted</div> <div> giardiasis, no cysts were identified in the suspect water, there was no association between</div> <div> water consumption rates and the likelihood of the disease, and the authors categorically discounted</div> <div> food-borne or fecal-oral spread, stating that it had never been reported (correct at the time).2</div> <div> <B>Personal observations</B></div> <div> I started visiting the Sierra Nevada in the early 1950s and have spent much of my free time there. I</div> <div> have never treated the water, and I have never had symptoms of giardiasis as a consequence of my</div> <div> visits. My many similarly active friends and acquaintances also drink the water with no ill effects. But</div> <div> because of other organisms possibly present, we are always careful to ?drink smart?:</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >Drink from large fast-flowing streams whenever possible, preferably those entering from the</FONT></div> <div> side rather than those paralleling the trail.</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >Drinking water from a lake is best advised at the inlet, with the next best place at the outlet?</FONT></div> <div> especially if it is fast-flowing.</div> <div> <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >• </FONT>Few <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts survive harsh Sierra winters. Contamination begins essentially anew each</div> <div> year, so springtime water is safer than summer or fall.</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >Water at higher elevations is safer than lower, partly because of reduced human and animal</FONT></div> <div> presence up high, and partly because water flowing to lower elevations picks up more</div> <div> contaminants the more distance it travels.</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >The colder the water is, the more likely it is freshly melted, meaning less opportunity for</FONT></div> <div> contamination.</div> <div> <FONT SIZE="2" COLOR="#000000" FACE="SymbolMT" >• </FONT>Because filtration of water through soil removes <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts, deep well water is considered</div> <div> safe.7 By implication, springs in the wilderness should be, too.</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >One would think that, after a heavy snow year when streams run full and long, some kind of</FONT></div> <div> ?flushing out? effect of lakes and streams must be occurring. Conversely, it makes sense to</div> <div> be more cautious in dry years.</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >Avoid water that likely could have passed through an area subject to heavy human or animal</FONT></div> <div> use.</div> <div> • <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >If it doesn?t look good?it?s cloudy or has surface foam?treat it or don?t drink it.</FONT></div> <div> ? Author?s words.</div> <bR> <div> If in doubt, treat it?but how? While useful in many instances, chlorine is not in general effective</div> <div> for <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>disinfection, which is why swimming pools are primary sources for the disease. The best</div> <div> filters work, although they are costly, heavy, and bulky, and many are somewhat awkward to use.8, 45</div> <div> Boiling is usually inconvenient, but if you are preparing hot water for meals anyway, you may as</div> <div> well take advantage. <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts are highly susceptible to heat, and simply bringing water to 150? F.</div> <div> for five minutes, 176? for a minute, or 190? momentarily, will kill them.8, 10 But boiling for a few</div> <div> minutes at altitude is usually recommended because of the other organisms that may be present. At</div> <div> 10,000 feet elevation, water boils at 194?; at 14,000 feet, 187?.</div> <div> Iodine is probably the best treatment choice, being inexpensive, convenient, and safe. Iodine is</div> <div> effective against most bacteria and viruses, too?and over a wide range of temperatures. (But</div> <div> Cryptosporidium may be resistant to iodine.) A popular system uses iodine crystals in a saturated water</div> <div> solution. Methods exist to mask or remove the iodine taste.</div> <div> <B>Summary figures</B></div> <div> Here are some of the <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cyst concentrations discussed in various places above. Units are cysts</div> <div> per liter.</div> <div> Concentration Comment</div> <div> ~1000 Typical swimming pool contamination</div> <div> ~100 Giardiasis is plausible**</div> <div> ~10 Minimum needed to contract giardiasis**</div> <div> ~1 Some wilderness water outside California</div> <div> 0.12 Some San Francisco water</div> <div> 0.108 Worst Sierra Nevada water</div> <div> 0.030 Los Angeles Aqueduct water</div> <div> 0.013 Mt. Whitney at Trail Camp</div> <div> 0.003 Mt. Whitney at Whitney Portal</div> <div> <B>Conclusions</B></div> <div> In a recent letter46 the Supervisor of the Inyo National Forest told me: ?As to whether or not</div> <div> <I>Giardia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >exists in the Sierra, we are not in a position to state a fact one way or the other.? This is a</FONT></div> <div> significant admission. So why do they persist in informing everyone that giardiasis is a potential hazard</div> <div> when visiting the Sierra Nevada?</div> <div> First: They know that some waters might be contaminated by something, and <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>is the</div> <div> organism on people?s minds so needs no elaboration. Contaminated water is certainly possible at lower</div> <div> elevations and in some locales. Noting in particular that novice hikers cannot be expected to make</div> <div> correct choices of which sources may be safe to drink, they point out that a conservative approach is to</div> <div> treat <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>all </I></FONT>water.</div> <div> Second: If a person believes, albeit incorrectly, that they contracted giardiasis from Sierra Nevada</div> <div> water, they cannot accuse the Forest Service of not warning them. Potential confrontations are therefore</div> <div> avoided.</div> <div> Unfortunately, this approach results in an incorrect perception of overall water quality in the Sierra</div> <div> by the general public, tainting the image of this pristine wilderness. It also means that if someone</div> <div> contracts a gastrointestinal illness after a visit, they will be more apt to blame the water, having been</div> <div> ?forewarned? that all water is suspect. And so the myth is perpetuated.</div> <div> ** If one liter is consumed.</div> <div> Untreated Sierra Nevada water is, almost everywhere, safe to drink?if you ?drink smart.? If you</div> <div> don?t ?drink smart? you may ingest diarrhea-causing organisms. But it almost certainly won?t be</div> <div> <I>Giardia</I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >.</FONT></div> <div> Because up to 1 in 14 of us carries the <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>parasite, we all need to do what we can to keep the</div> <div> water pure. Defecate away from water, and bury it or carry it out.</div> <div> Camp cooks in particular need to pay special attention to cleanliness. Wash hands thoroughly,</div> <div> especially before handling utensils and preparing meals. If you contract giardiasis in the backcountry,</div> <div> blame your friends?not the water.</div> <div> High Sierra water has far too few <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts for you to contract an infestation from it. Even if</div> <div> you go somewhere where the concentration is high, you probably won?t get giardiasis. If you do get</div> <div> giardiasis, you probably won?t have any symptoms. If you have symptoms, they will probably go away</div> <div> by themselves in a week or so. If they don?t or you develop serious persistent symptoms, you should</div> <div> seek medical treatment. Finally, those contracting giardiasis may develop immunity to it, thus lowering</div> <div> the likelihood that they will get it again.</div> <div> There is certainly no reason for anxiety about giardiasis. Fewer than 1 percent of those who have an</div> <div> infestation, or about 5 percent of those with symptoms, need medical help.</div> <div> <B>Recommendation</B></div> <div> Our wilderness managers are in a position to educate the outdoor public about the real culprit in the</div> <div> <I>Giardia lamblia </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >story: inadequate human hygiene. When they realize that Sierra Nevada water has</FONT></div> <div> fewer <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia </I></FONT>cysts than, for example, the municipal water supply of the city of San Francisco, maybe</div> <div> they will turn their attention to it.</div> <div> The thrust of the following observation is long overdue:</div> <div> <I>?Given the casual approach to personal hygiene that characterizes most backpacking</I></div> <div> <I>treks, hand washing is likely to be a much more useful preventative strategy than water</I></div> <div> <I>disinfection!</I></div> <div> <I>?? This simple expedient, strictly enforced in health care, child care, and</I></div> <div> <I>food service settings, is rarely mentioned in wilderness education materials.?2</I></div> <div> <B>About the author</B></div> <div> Bob Rockwell is an active mountaineer who made his first trip into the Sierra Nevada in 1952 to</div> <div> climb Mt. Whitney, and he repeats this climb several times annually. He has a bachelor?s degree in</div> <div> Physics from UC-Berkeley, and a PhD in Aeronautical and Astronautical Engineering (Biomechanics)</div> <div> from Stanford. In the course of making over a thousand ascents of hundreds of individual Sierra Nevada</div> <div> mountains, he has never filtered or otherwise treated the water and he has never contracted symptoms of</div> <div> giardiasis. Retired since 1990, he is now able to fully indulge in his favorite pastime and spends more</div> <div> time there, never treating the water, than ever before.</div> <div> <B>References</B></div> <div> 1 Wilkerson, James A., MD: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Medicine for Mountaineering and Other Wilderness Activities. </I></FONT>The</div> <div> Mountaineers, 4th edition, 1992</div> <div> 2 Welch, Thomas R. and Welch, Timothy P.: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardiasis as a Threat to Backpackers in the United</I></FONT></div> <div> <I>States: A Survey of State Health Departments. </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >Wilderness and Environmental Medicine, Vol. 6, 1995</FONT></div> <div> 3 Rockwell, Bob: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardiasis: Let?s Be Rational About It. </I></FONT>Summit Magazine, Nov.-Dec. 1987</div> <div> 4 Rockwell, Bob: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia Lamblia and Giardiasis, with Implications for Sierra Nevada Visitors.</I></FONT></div> <div> California Mountaineering Club Newsletter, Vol. 7 no. 2, April 1996</div> <div> ?? Emphasis is in the original.</div> <bR> <div> 5 Rockwell, Bob: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardia Update. </I></FONT>California Mountaineering Club Newsletter, Vol. 8 no. 2, April 1997</div> <div> 6 Juranek, Dennis D.: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardiasis</I></FONT>. Centers for Disease Control and Prevention, 1990</div> <div> 7 Swartz, Morton N., MD: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Intestinal Protozoan Infections</I></FONT>. Scientific American Medicine, 1994</div> <div> 8 Kerasote, Ted: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Great Outdoors; Drops to Drink</I></FONT>. Audubon, July 1986</div> <div> 9 <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Microbial Risk Assessment for Reclaimed Water. </I></FONT>EOA, Inc., Final Report. Prepared in Association</div> <div> with the University of California School of Public Health, Oakland, CA. May 1995</div> <div> 10 Backer, Howard D.: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardiasis: An Elusive Cause of Gastrointestinal Distress. </I></FONT>The Physician and</div> <div> Sportsmedicine, Vol. 28 no. 7, July 2000</div> <div> 11 DeReigner D. P., et al: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Viability of Giardia Cysts Suspended in Lake, River, and Tap Water. </I></FONT>Applied</div> <div> Environmental Microbiology, Vol. 55 no. 5, 1989</div> <div> 12 Olson, M. E: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Human and Animal Pathogens in Manure. </I></FONT>Conference on Livestock Options for the</div> <div> Future. Winnepeg, Manitoba, June 2001</div> <div> 13 Olsen, M. E., et al: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Survival of Giardia Cysts and Cryptosporidium Oocysts in Water, Soil and Cattle</I></FONT></div> <div> <I>Feces. </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >American Association of Veterinary Parasitologists, 43rd Annual Meeting, 1998</FONT></div> <div> 14 <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Fact Sheet on Enteric Protozoa and the Food Industry. </I></FONT>National Food Processors Institute, October</div> <div> 1998.</div> <div> 15 Moser, Penny Ward: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Danger in Diaperland</I></FONT>. Health, September/October 1991</div> <div> 16 Suk, Thomas: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Eat, Drink and Be Wary. </I></FONT>California Wilderness Coalition</div> <div> 17 Berkow, Robert, MD, Editor: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Parasitic Infections?Giardiasis</I></FONT>. The Merck Manual, 14th edition,</div> <div> 1997</div> <div> 18 Wilkerson, James and Caulfield, Page: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Wilderness Water Disinfection</I></FONT>. Appalachia, No. 4, Winter</div> <div> 1985-86</div> <div> 19 Bemrick, W. J.: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Some Perspectives on the Transmission of Giardiasis. </I></FONT>Giardia and Giardiasis:</div> <div> Biology, Pathogenesis and Epidemiology, Erlandsen and Meyer, Editors, Plenum Press, 1984</div> <div> 20 Feachem, R. G., et al: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Sanitation and Disease: Health Aspects of Excreta and Wastewater</I></FONT></div> <div> <I>Management</I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >. John Wiley and Sons, 1983</FONT></div> <div> 21 <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Communicable Diseases in California, 1994, 1995. </I></FONT>State of California Department of Public Health<FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>.</I></FONT></div> <div> 22 Vitusis, Ziegfried, chief microbiologist at the EPA. Quoted in Backpacker, Dec. 1996</div> <div> 23 Kappus KD, Lundgren RG and Juranek DD: <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Intestinal Parasitism in the United States: Update on a</I></FONT></div> <div> <I>Continuing Problem. </I><FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman" >American Journal of Tropical Medicine and Hygiene. Vol. 60 no. 6, 1994</FONT></div> <div> 24 <FONT SIZE="2" COLOR="#000000" FACE="TimesNewRoman,Italic" ><I>Giardiasis Surveillance?United States, 1992?1997. </I></FONT>Centers for Disease Control and Prevention,</div> <div> August 2000.</div> <div> 25 Porter, J. 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