[pct-l] Water borne diseases--more info about Giardia

[Maxine Weyant]

Your friend Professor Rockwell very kindly reviewed a lot of literature and provided his readers with a helpful distillation of information from a number of studies, but his PhD is in physics or engineering, not microbiology, and his article is laced with some anecdotal information and conclusions that may or may not be correct and could lead to some unsafe practices among current readers. 

Most of the data was from the 1980's with an update in 1997.  The Sierras water conditions may not be the same as it was then.  There was a time when people could drink from nearly all mountain streams and lakes in the US and now we can't--because Giardia is probably way more prevalent than it was decades ago and it has reached places where it didn't previously exist. While it may not thrive under freezing conditions, Giardia continually gets reintroduced into the high country every year by wildlife, especially deer, as well as humans, dogs, cattle, and possibly even horses, mules, and llamas. (I don't know for a fact that horses or llamas can carry Giardia, just surmising here.)  SInce humans may be asymptomatic carriers, they bring it with them by defecating, but they can also shed the cysts when they bathe in lakes and streams and they can carry some on their shoes.  If animals eat human feces or toilet paper, or dig up their catholes, they can become colonized too.  Birds landing in high mountain lakes can carry lots of things from other bodies of water on their feathers, which is how fish eggs are often transported into the high country lakes.  So the number and variety of organisms in certain areas are constantly evolving and new diseases keep emerging over the years--West Nile Virus, Lyme disease, Rocky Mt Spotted fever, funguses that infect trees, parasites and worms that infect fish, etc.    

The Sierras water sources are also quite different in August than they are in June.  Water rushing hard and fast from yesterday's snowmelt will not be carrying many organisms, but the babbling brooks and sun-warmed lakes of August harbor a different spectrum of organisms.  The animals have come out of hibernation or have returned to the high country, the cows that have grazing rights in the sections between Sonora Pass and Truckee have meandered into the higher mountain meadows and are defecating all over the trail and in the streams.  The trail gets covered with a fine layer of horse and mule droppings, and the flies show up, and humans walk through it all and carry it all into streams they cross.  They can also carry organisms into their mouths from their hands, including giardia cysts, from touching their shoes, the dust on their legs, their hiking pole handles, the nozzles on their water bladders, and from leaning on the ground or folding their tarps, etc…  The other thing that happens in late summer is there is more sediment and solids suspended in water and many organisms coalesce into biofilms and slimes that allow organisms to attach to a solid and make it harder for chemicals to penetrate and kill them.  These biofilms can plug up water filters and apparently can start to grow in water filters that are dirty or old.  You can read about that in an article "Efficacy of Chemical Water Treatment Technologies in the Backcountry" by going to the website for Aqua Mira drops and linking to it from there.  The article concludes that Iodine cannot effectively penetrate biofilms, and regular chlorine is not especially effective either.  Chlorine dioxide, which is the active ingredient in Aqua Mira drops and tabs, was the most effective chemical in their study for penetrating biofilms and killing organisms and was less negatively-affected by cold temperatures than the other substances.  Bear in mind that there could be a commercial bias since Aqua Mira stands to benefit from this info, but the article first appeared in BackpackingLight Spring 2005 and the authors do not work for Aqua Mira.  Note that while they mentioned that filters can get "infected" the study didn't really include filters or whether pre-filters can trap the biofilm sufficiently.  

I think Mr Rockwell erroneously concluded that what was making everyone sick repeatedly on his trip in the Himalayas was giardia because he was assured that the Sherpas handled the food safely.  Giardia tends to take 1-3 weeks for symptoms to show up and can last for 1-2 weeks, often longer.  I'm not saying he's wrong because no one was tested, but what he's describing is what is typically seen with bacterial food-borne illnesses, just like the kind you can get in any other developing country from eating unpeeled or undercooked fruits and vegetables or foods chopped on contaminated cutting boards, etc.  I doubt highly that the Sherpas were cleaning their cutting boards with bleach, or had been rigorously washing their hands all the time, or that they really understood what "germs" are.  We had the same problem in Tibet where some members in my group kept getting sick, and they got immediately better after taking Cipro, which treats certain bacteria but does not treat Giardia.  The problem stopped after I made the Tibetan guides soak our fruits and vegetables in iodine treated water using drops I had gotten to clean fruits with in Mexico.  I'm pretty sure they were just cutting up clean-looking tomatoes and cucumbers, etc. which they served to us raw.  Yes, this is an anecdote too, so bear that in mind.  

So, you can read the info from his article and decide to take your chances in the Sierras and you might do just fine, especially just after snowmelt.  It's your choice.  But if you get sick and ruin your trip, or someone else's, or if you have to be evacuated, then the consequences are not negligible.  We know that a lot of PCT hikers get sick somewhere around the Kern River or after Kennedy Meadows and, while it may not be from giardia,  it still matters--and they could have avoided getting sick had they taken precautions.   His article may also lead you to conclude that you're more likely to have minimal or no symptoms if you get Giardia.  I had Giardia many years ago from drinking from a waterfall in Mexico, before I knew better.  I was quite sick at first, but assumed it was just "turista" bacterial infection that would clear up like the others did.  I felt better after 2-3 weeks but still couldn't eat eggs, peanut butter, or anything with fat without having severe diarrhea.  I was pretty young then, finally saw a doctor in the US after about a month, giardia was confirmed with a stool sample, and by that time I had lost 10-15 lbs and weighed 93 lbs!  My dog got giardia a month ago from drinking from a stream in British Columbia.  He was so sick, he needed IV fluids in addition to the antibiotics.  Obviously, my own anecdotal experiences affect my own judgement and what I do.  

Respectfully submitted,  

Dys-feng shui-nal