Giardia Lamblia and Giardiasis
With Particular Attention to the Sierra Nevada
By
Robert L. Rockwell
Figure
1. Giardia lamblia
trophozoites as they appear with the scanning electron microscope.[*]
Ask the
average outdoors person about Giardia
lamblia or giardiasis, and they have
certainly heard about it. Almost
always, however, they are considerably misinformed about both the organism’s
prevalence in wilderness water, and the seriousness of the disease if
contracted.
With the
advent of the Internet, the amount of information one can easily find on the
subject is voluminous. Unfortunately,
most of it is flawed in important aspects, being unsubstantiated, anecdotal, or
merely quoting other unsubstantiated and anecdotal articles. Official sources, such as many informational
publications put out by the US government, are not immune to this criticism.
This paper is
the result of a critical distillation of relevant articles, retaining only
those from scholarly, peer-reviewed, or otherwise professional and trustworthy
sources.
One
conclusion of this paper is that you can indeed contract giardiasis on visits
to the Sierra Nevada, but it won’t be from the water. So drink freely and confidently:
Proper personal hygiene is far more important in avoiding giardiasis
than treating the water.
First, an
excerpt written by a highly regarded wilderness physician:
“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 (far less than enough to be
infective), and erected garish signs proclaiming the water ‘hazardous.’”[1]
And another,
by researchers who surveyed the health departments in all 50 states and scanned
the medical literature looking for evidence that giardiasis is a significant
threat to outdoor folk:
“Neither
health department surveillance nor the medical literature supports the widely
held perception that giardiasis is a significant risk to backpackers in the
United States. In some respects, this
situation resembles (the threat to beachgoers of a) shark attack: an extraordinarily rare event to which the
public and press have seemingly devoted inappropriate attention.”[2]
I explored
this subject in 1987[3] and again in 1996[4]
with an update in 1997.[5] The conclusions have always been that the “Giardia problem” in Sierra Nevada water
is grossly exaggerated, and that the cases of giardiasis subsequent to
wilderness visits are wrongly blamed on the water. After incorporating the recent information for this paper, those
prior conclusions are not only still valid but also considerably reinforced.
Just who is this
little guy, anyway? [6], [7], [8], [9], [10]
Giardia lamblia, now also known as G. intestinalis or G. duodenalis, was first observed in 1681 by Anton
van Leeuwenhoek, inventor of the microscope.
The parasite was named in 1915 for two scientists who studied it: Prof. A. Giard in Paris and Dr. F. Lambl in
Prague.
Giardia is a flagellated (having whip-like
appendages for locomotion) protozoan that, in the trophozoite (active) form,
attaches itself with an adhesive disk to the lining of the upper intestinal
tract of the host animal. There, it
feeds and reproduces. Trophozoites
divide by binary fission about every 12 hours.
Thus, a single parasite can theoretically result in more than a million
in 10 days and a billion in 15 days.
At some time
in its active life, the trophozoite releases its hold on the bowel wall and
floats in the fecal stream. As it makes
its journey, it transforms into an egg-like structure called a cyst, which is
eventually passed in the stool.
Duration of cyst excretion, called shedding, may persist for
months. Once outside the body, the
cysts can be ingested by another animal.
Then, they “hatch” into trophozoites due to stomach acid action and
digestive enzymes, and the cycle repeats.
The
trophozoite is 9 - 15 mm
long, 5 - 15 mm wide,
and 2 - 4 mm
thick. Unlike the cyst, it cannot live
for long outside a host. Cysts are 8 -
12 mm long by 6 - 9
mm in diameter; so a million could fit
under a fingernail. Cysts can survive
for as long as 2 to 3 months in cold water,10, [11] but
they cannot tolerate freezing.9, [12]
A significant
infestation can leave millions of trophozoites stuck tight to the intestinal
lining. There, they cripple the gut’s
ability to secrete enzymes and absorb food, especially fats, thereby producing
the disease’s symptoms. The symptoms typically
appear one to two weeks after ingestion, with an average of nine days, but four
weeks is not uncommon. Symptoms can
vanish suddenly and then reappear. They
may hide for months. They may not
appear at all.10,
[13]
There are
three ways that giardiasis, the disease caused by ingesting Giardia
cysts, can be contracted: contaminated
water, contaminated food, and direct fecal-oral. A person who has just come down with the disease and who wishes
to identify the source needs to reflect on not only the possibility of each of
these, but in a suspect period ranging from typically one week to four weeks
earlier.
The bad news: Giardia lamblia is
almost everywhere 1, 6, 7, 8, 9,
10, [14], [15], [16], [17],
[18],
[19]
Giardiasis
has been most often associated with travel to such places as Latin America,
Africa, Asia, and the former Soviet Union.
However, Giardia has always
been present in wilderness streams, in the water supplies of most cities around
the world, and even in the municipal water of large US cities. In fact, in the 1930s and 1940s, before
regulated municipal water treatment plants, everyone was drinking Giardia all the time.[20]
Currently, Giardia lamblia is the most commonly
diagnosed intestinal parasite in North America.22 It is
the most frequently identified cause of diarrheal outbreaks associated with
drinking water in this country. Fully
20 percent of the world’s population is infected, and up to 7 percent of
Americans, most without any symptoms at all.10, [21] The Centers for Disease Control and
Prevention (CDC) estimates that as many as 2,500,000 cases occur annually in
the US or almost one for every 100 persons.[22]
Infestation
rates of 60 percent of the children in day care centers across the country have
been noted. Institutions for mentally
retarded persons can have high rates.
Other high-rate populations include promiscuous male homosexuals,
international travelers, and patients with cystic fibrosis. And family members of these individuals.
In an
incident in New Jersey a child had a “fecal accident” in a 700,000-liter
swimming pool, and nine swimmers came down with the disease.[23] How many Giardia
cysts might have been involved? The
number of cysts shed in feces is highly variable but has been estimated as high
as 900 million per day for humans.
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[†]. Water collected
in Hetch Hetchy already meets governmental standards for drinking water and is
not required to be filtered before distribution because of its high quality.[24]
The Los Angeles Aqueduct, which transports water to that city from the
eastern slopes of the Sierra Nevada, averages 0.03 cysts per liter.[25]
Drinking
highly contaminated water is one way to get the disease. Less common in developed countries is direct
passage from stool to the hands of a food preparer and then to the food
itself. When 16 people got sick from
the salad at a Connecticut picnic, the CDC tracked the source to a woman who
had mixed the salad with her hands. She
didn’t have giardiasis, but one of her children did—without any symptoms.13 A similar situation occurred in New Jersey,
with the salad preparer testing positive for Giardia along with her
child and pet rabbit.[26]
Contaminated
food may be a less-common source for the general population, but for wilderness
visitors, it may be the most important one.
Put another way: If the water is
clean, food-borne and direct fecal-oral routes are the only pathways.
On a recent
climbing expedition to Tibet, members of our party came down again and again
with what was undoubtedly giardiasis.
Our water came from glacial melt, but all our food in advanced base camp
and below was prepared by Sherpa cooks.
Much of the food they prepared—potatoes, rice, cauliflower, cabbage,
onions—came from Nepal. We were
continually assured that the cooks were practicing good hygiene, yet we had
major intestinal problems that prevented many of the participants from getting
high on the mountain.
The disease
has been referred to as “beaver fever” because of a presumed link to those
water-dwelling animals known to be carriers.
However, it has been suggested that it is more likely that humans have
carried the parasite into the wilderness and that beavers may actually be the
victims. In particular, there is a
growing amount of data showing that beavers living downstream from campgrounds
have a high Giardia infection rate
compared with a near-zero rate for beavers living in more remote areas.
In any case,
beavers can and do contract giardiasis.
Being water-dwellers, they are thus able to contaminate water more
directly than an animal that defecates on the ground.
Other animals
that can harbor Giardia are bighorn
sheep, cats, cattle, coyotes, deer, dogs, elk, muskrats, pet rabbits, raccoons,
and squirrels. But not horses and
domestic sheep. And naturally occurring
infections have not been found in most wild animals including badgers, bears,
bobcats, ferrets, lynxes, marmots, moose, porcupines, rabbits, and skunks.
If “It’s
everywhere!” why is it not more of a
problem?
The good news: Most of the time, the concentration of Giardia cysts is very low 1, 6, 8
Outside of
places where dirty diapers congregate and cities where water treatment plants
break down or are ineffective, there is little room to worry. A few Giardia
cysts now and then will cause no harm and in fact may be useful in developing
an immunity as will be mentioned later.
How many
cysts does it take to get the disease?
Theoretically only one, but volunteer studies have shown that 10 or so
are required to have a reasonable probability of contracting giardiasis: About one-third of persons ingesting 10 – 25
cysts get detectable cysts in their stools. 6, 7, 8, 10, [27],
[28]
But be
careful with statistics: Animal
droppings containing 100,000 Giardia
cysts deposited at the 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 immediate vicinity of
the deposit, the concentration can be much higher.
A comforting
observation is that significant cyst inactivation, as high as 99.9 percent, can
occur as a result of anaerobic digestion in sewage sludge.[29] Of course, using a simple cat hole is not
exactly a good approximation to the sewage plant process, but this points out
the wisdom of doing something better than just leaving it on the ground or
under a rock.
Since cysts
that “winter over” in the Sierra Nevada are either in liquid water for
considerably more than 2 to 3 months or exposed to freezing temperatures, it
would appear that few will survive the harsh Sierra winters. So, except for pollution by winter
mountaineers and non-hibernating animals, Giardia contamination in the
high country must begin essentially anew each spring.
More good news: If you have a Giardia
infestation, you will likely have no symptoms 1, 6, 7, 15, 16, [30], [31]
The symptoms
of giardiasis vary widely.
Characteristic symptoms, when they occur, are 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. Stools are soft (but not
liquid), bulky, and foul smelling. They
have been described as greasy and frothy, and they float on the surface of
water. Nausea, weakness, and loss of
appetite may occur. Studies have shown
that giardiasis can be suspected when the illness lasts seven or more days with
at least two of the above symptoms.7
However, most
infected individuals have no symptoms at all!
In one incident1 studied by the CDC, disruption in a major
city’s water disinfection system allowed the entire population to consume water
heavily contaminated with Giardia. Yet only 11 percent of the exposed
population developed symptoms even though 46 percent had organisms in their
stools. These figures suggest that (a)
even when ingesting large amounts of the parasite, the chance of contracting
giardiasis is less than 1 in 2, and (b) if you are one of the unlucky ones to
contract it, the chance of having symptoms is less than 1 in 4. But perhaps the most telling statistic is
that drinking heavily contaminated
water resulted in symptoms of giardiasis in only 1 case in 9.
If you have symptoms
it may not be giardiasis 1, 7, 13, 16, [32]
Many people
claim that they “got it” on a particular trip into the wilderness. Yet upon questioning, they usually report
that the presence of Giardia was not
confirmed in the laboratory. (Only
8 percent of persons with a diarrheal illness in this country seek medical
care.22) Depending on the situation, other possible
offenders are Campylobacter, Cryptosporidium, Salmonella, Shigella, Yersinia,
Aeromonas, Clostridium, and Escherichia coli, with the last being the most
common cause of traveler’s diarrhea worldwide.
Food poisoning is also a possibility.
Cryptosporidiosis,
in particular, is a growing problem in this country, and currently, there is no
effective treatment for it. An outbreak
in Milwaukee in 1993 caused 403,000 people to become ill and 100 to die. A year later, 43 people in Las Vegas died from
the same disease.[33]
The severity of cryptosporidiosis depends on the condition of the
host’s immune system. In immunologically
normal people, symptoms and duration are similar to those of giardiasis. But in persons whose immune systems have
been compromised (e.g., AIDS victims), symptoms can be profound: Frequent (6 to 25), voluminous (1 to 25
liters) daily bowel movements, serious weight loss, and cyst shedding often
persist for months.
The diarrhea
being blamed on Giardia from that
climbing trip a week ago may instead be due to some spoiled food eaten last
night or Campylobacter in undercooked chicken four days ago. Or because the incubation period is usually
from one to four weeks, even if it is giardiasis the uncertainty range
indicates that the culprits could have been ingested anytime during a full
three weeks worth of meals and beverages.
People in high-risk groups for Giardia, such as family members of
children in day care centers or promiscuous male homosexuals, have even more
possible sources to consider. To indict
a particular stream or lake under such circumstances, without being able to at
least verify that cysts are indeed there at all, is illogical at best.
The type of
diarrhea can help in the diagnosis: If
it is liquid and mixes readily with water rather than floating on top and is
not particularly foul smelling, the problem is likely something other than
giardiasis. Diarrhea which lasts less
than a week, untreated, is probably not from giardiasis.
Almost always,
giardiasis goes away without treatment 1, 6, 7, 13, 14, 15, 30, [34]
If you are
unlucky enough to get giardiasis with symptoms, the symptoms will probably go
away in a week or so without treatment.
You may still be harboring the cysts, however, and can unknowingly
spread the disease. Thus, practicing
commonly recommended wilderness sanitary habits—defecating 100 feet from water,
burying or packing out feces and toilet paper, washing before handling food,
etc.—is an excellent idea.
The Food and
Drug Administration, observing that giardiasis is more prevalent in children
than adults, suggests that many individuals seem to have a lasting immunity
after infection.[35] Furthermore, citizens of cities and
countries where the parasite is numerous clearly seem to have few if any
problems with their own water, which also points to an acquired immunity. So there is a possible bright side to
contracting the disease.
Looking for
cysts and trophozoites in stool specimens under the microscopic has been the
traditional method for diagnosing giardiasis, but it is notoriously
unreliable. Now, however, an
immunologic test (enzyme-linked immunosorbent assay, or ELISA) for the
detection of Giardia antigens in
stool samples is available. The
antigens are present only if there is a Giardia
infection. ELISA is a big improvement
over the microscopic search, with detection sensitivities of 90 percent or
more.
Rare
individuals not only do not spontaneously rid themselves of the organisms but
instead develop serious symptoms of malabsorption, weight loss, ulcer-like
stomach pain, and other chronic disturbances.
Fortunately, this occurs in fewer than 1 percent of those with
infestations. These unlucky people need
medical treatment.
Metronidazole
(Flagyl) has been the standard medication, with about a 92 percent cure
rate. Recommended by the CDC, it is not
approved by the FDA for giardiasis because it can have some serious side
effects and is potentially carcinogenic.
Quinacrine (Atabrine) and furazolidone (Furoxone) are also
prescribed. Tinidazole (Tinebah) is
highly effective in single doses and is widely used throughout the world, but
it is not available in the US; it can be purchased over-the-counter in many
developing countries.7, 22
Giardiasis
has been called a disease of “somes.”
Some people do not contract it even from heavily contaminated
sources. Some infestations vanish with
no treatment at all. Some people become
asymptomatic carriers. Some evidence
suggests that some people acquire a natural immunity to some strains. And some strains seem more virulent than
others.13
The problem
may not be whether you are infected with the parasite but how harmoniously you
both can live together. And how to get
rid of the parasite when the harmony does not exist or is lost.6
So, what about the
Sierra Nevada? 1, 6, 7, 8, 14, 16
In 1984, the
US Geological Survey in cooperation with the California Department of Public
Health examined water at 69 Sierra Nevada stream sites that were selected in
consultation with Park Service and National Forest managers.[36] Forty-two of the stream sites were
considered “high-use” (high probability of human fecal contamination), and 27
were “low-use.” Cysts were found at
only 18 (43 percent) of the high-use sites and at 5 (19 percent) of the low-use
sites. The highest concentration of Giardia cysts was 0.108 per liter of
water in Susie Lake, south of Lake Tahoe.
The next highest was 0.037 per liter near Long Lake, southwest of
Bishop. Samples taken in the Mt.
Whitney area varied from 0 (most sites) to 0.013 (Lone Pine Creek at Trail
Camp) per liter. The concentration was
0.003 per liter in Lone Pine Creek at Whitney Portal.
Recall that
San Francisco water can contain a concentration of 0.12 cysts per liter,24 a figure now seen to be higher than that
measured anywhere in the Sierra. San
Francisco city officials go to great lengths to assure their citizens that the
water is safe to drink, and if true—as it most assuredly must be—this
comparison alone is quite revealing.
Even Los
Angeles Aqueduct water, with only 0.03 cysts per liter,25 has a higher concentration of Giardia
than all but two of the 69 Sierra sites examined.
Taking the
highest concentration measured in the Sierra (0.108), we can make some
calculations. The probability[‡]
of finding 10 or more cysts in a liter of water—to have at least a one-third
chance of contracting giardiasis—is about 10-17. Ten cysts in 10 liters of water, about 10-7. In fact, one would have to drink over 89
liters to have a 50 percent probability of ingesting 10 or more cysts.
A word of
caution: The concentration is never
uniform, as suggested by the “lake incident” above.
Another
reason for caution: 1984 was some time
ago, and areas of the Sierra may be differently contaminated now: perhaps more, perhaps less. Also, while so much attention is being given
to Giardia, there are worse organisms
to worry about such as Campylobacter, Cryptosporidium, E. coli, and the other
organisms mentioned earlier.
In an
informative study,[37]
investigators contacted thousands of visitors to one of the high-use sites
during the summers of 1988 through 1990.
Water samples taken on 10 different dates at each of three locations
exhibited Giardia cyst concentrations
between 0 and 0.062 (average 0.009) per liter.
A goal was to enlist volunteers who were cyst-negative before their
trip, verified by stool analysis, and then determine what fraction were cyst
carriers after the trip. Unfortunately,
stool collection is not a particularly enjoyable task, and only 41 people
agreed to participate. Of these, two
acquired Giardia cysts during their
trip, but neither came down with symptoms.
Six of the others exhibited post-visit intestinal symptoms, but none
tested positive for Giardia
(interestingly, all six had filtered their water). In sum, no cases of laboratory-confirmed symptomatic giardiasis
were found.
The water
that wilderness travelers are apt to drink, assuming that they use a little
care, seems almost universally safe as far as Giardia is concerned. The
study referred to earlier,2 in which the researchers concluded that the
risk of contracting giardiasis in the wilderness is similar to that of a shark
attack, is telling. What they did find
is that Giardia and other intestinal
bugs are for the most part spread by direct fecal-oral or food-borne
transmission, not by contaminated drinking water. Since personal hygiene often takes a backseat when camping, the
possibility of contracting giardiasis from someone in your own party—someone
who is asymptomatic, probably—is real.
Recalling that up to 7 percent of Americans, or 1 in 14, are infected,
it is not surprising that wilderness visitors can indeed come home with a case
of giardiasis contracted not from the water…but from one of their friends.
This theme,
that reduced attention to personal hygiene is an important factor for
contracting giardiasis in the wilderness, is becoming more frequent in the
literature.2, 10, 14, 37, [38]
Outside of
the Sierra, Giardia cysts in
concentrations “as high as four per gallon[§]”
have been detected in untreated water in northeastern and western states.[39] But even with this concentration, one would
have to consume over nine liters of water to have a 50 percent chance of
ingesting 10 or more cysts.
Indeed, there
may be as much unwarranted hysteria surrounding Giardia in wilderness water in these other areas as there is for
the Sierra. For example, an oft-cited
report describing acquisition of the disease by 65 percent of a group of
students hiking in the Uinta Mountains of Utah[40]
is now viewed with considerable skepticism.
Specifically, the attack rate was far beyond that usually seen with
water-contracted giardiasis, no cysts were identified in the suspect water,
there was no association between water consumption rates and the likelihood of
the disease, and the authors categorically discounted food-borne or fecal-oral
spread, stating that it had never been reported (correct at the time).2
Personal
observations
I started
visiting the Sierra Nevada in the early 1950s and have spent much of my free
time there. I have never treated the
water, and I have never had symptoms of giardiasis as a consequence of my
visits. My many similarly active
friends and acquaintances also drink the water with no ill effects. But because of other organisms possibly present,
we are always careful to “drink smart”:
·
Drink from
large fast-flowing streams whenever possible, preferably those entering from
the side rather than those paralleling the trail.
·
Drinking
water from a lake is best advised at the inlet, with the next best place at the
hopefully fast-flowing outlet.
·
Few Giardia
cysts survive harsh 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.7 By
implication, springs in the wilderness should be, too.
·
One would
think that after a heavy snow year, when streams run full and long, some kind
of “flushing out” effect of lakes and streams must be occurring. Conversely, it makes sense to be more
cautious in dry years.
·
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.
If in doubt,
treat it—but how? While useful in many
instances, chlorine is not in general effective for Giardia disinfection, which is why swimming pools are primary
sources for the disease. The best
filters work, although they are costly, heavy, and bulky, and many are somewhat
awkward to use.8, [41]
Boiling is
usually inconvenient, but if you are preparing hot water for meals anyway, you
may as well take advantage. Giardia cysts are highly susceptible to
heat, and simply bringing water to 150° F. for five minutes,10 to 176° for a minute,8 or 190° momentarily, will kill them. But boiling for a few minutes at altitude is
usually recommended because of the other organisms that may be present. At 10,000 feet elevation, water boils at
194°; at 14,000 feet, 187°.
Iodine is
probably the best treatment choice, being inexpensive, convenient, and
safe. Iodine is effective against most
bacteria and viruses, too—and over a wide range of temperatures. (But Cryptosporidium may be resistant to
iodine.) A popular system uses iodine
crystals in a saturated water solution.
Methods exist to mask or remove the iodine taste.
Summary figures
Here
are some of the Giardia cyst concentrations discussed in various places
above. Units are cysts per liter.
Concentration Comment
~1000 Typical
swimming pool contamination
~100 Giardiasis is plausible[**]
~10 Minimum needed to contract giardiasis**
~1 Some wilderness water outside California
0.12 San Francisco water
0.108 Worst Sierra Nevada water
0.030 Los Angeles water
0.013 Mt. Whitney at Trail Camp
0.003 Mt. Whitney at Whitney Portal
Conclusions
In a recent
letter[42]
the Supervisor of the Inyo National Forest admitted: “As to whether or not Giardia exists in the Sierra, we are
not in a position to state a fact one way or the other.” This is a significant admission. So why do they persist in informing everyone
that giardiasis is a potential hazard when visiting the Sierra Nevada?
First: They know that some waters might be contaminated
by something, and Giardia is the organism on people’s minds so needs no
elaboration. Contaminated water is
certainly possible at lower elevations and in some locales. Noting in particular that novice hikers
cannot be expected to make correct choices of which sources may be safe to
drink, they point out that a conservative approach is to treat all
water.
Second: If a person believes, albeit incorrectly,
that they contracted giardiasis from Sierra Nevada water, they cannot accuse
the Forest Service of not warning them.
Potential lawsuits, for example to recoup medical expenses, are
therefore avoided.
Unfortunately,
this approach results in an incorrect perception of overall water quality in
the Sierra by the general public. It
also means that if someone contracts a gastrointestinal illness after a visit,
they will be more apt to blame the water, having been “forewarned” that all
water is suspect. And so the myth is
perpetuated.
Untreated
Sierra Nevada water should be, almost everywhere, safe to drink—if you “drink
smart.” If you don’t “drink smart” you
may ingest diarrhea-causing organisms.
But it won’t be 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.
Sierra Nevada
water has far too few Giardia cysts
for you to contract an 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.
Recommendation
Our
wilderness managers are in a position to educate the outdoor public about the
real culprit in the Giardia lamblia
story: inadequate human hygiene. When they acknowledge that Sierra Nevada
water has fewer Giardia cysts than,
for example, the municipal water supply of the city of San Francisco, maybe
they will turn their attention to it.
The thrust of
the following observation is long overdue:
“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! [††]
This simple expedient, strictly enforced in health care, child care, and
food service settings, is rarely mentioned in wilderness education materials.”2
About the author
Bob Rockwell
has a BS in physics from the University of California, Berkeley, and PhD in
biomedical engineering from Stanford University. He made his first trip into the Sierra Nevada in 1952 to climb
Mt. Whitney, and he repeats this climb several times annually. In the course of making over a thousand
Sierra Nevada ascents of hundreds of individual mountains, he has never
filtered or otherwise treated the water and has never contracted symptoms of
giardiasis. Retired since 1990, he is
now able to fully indulge in his favorite pastime and spends more time there,
enjoying the water, than ever before.
References