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Waterborne Pathogens
Posted by Biologist on Jan 06 2005
First Brian, I want to apologize for publicly contradicting you. My intention is not to ruffle your feathers, but the information you provided was inaccurate, misleading, and potentially dangerous.
Second, coliforms are bacteria, and most (not all) bacteria can be considered pathogens. Fecal coliforms, in particular are prevalent in streams year-round. Where do fecal coliforms originate? They come from the feces of warm blooded vertebrates. Giardia, on the other hand, is a Protist but is also considered a pathogen. Its hosts are also warm blooded vertebrates... not just beavers, humans, or sheep, but beavers have earned their reputation by living, urinating, and defecating primarily in the water, like otters.
Third, our hands are not inherently dangerous, though they have both resident and transient bacteria all the time. Frequently washing ones hands is good advice, because it reduces the likelihood of spreading pathogens into our mucous membranes and digestive tract. It’s particularly effective at reducing the likelihood of contracting pathogens that propagate through the fecal-oral pathway. While I’m on the topic, using antibacterial soap at home is a particularly bad idea because it allows natural selection to favor antibiotic-resistant bacterial strains. Then we’re left with a bunch of resistant bacteria that survive and reproduce more frequently than nonresistant strains. Perhaps antibacterial soap is more justified in the field where the frequency of bacteria encountering antibiotics is less. However, your alcohol suggestion is a much better strategy.
Fourth, Giardiasis is spread by contaminated food or water and by direct personal contact (e.g., by hand-to-hand then hand-to-mouth contact). Contracting Giardiasis via drinking water is associated with the "concentration" of giardia in the water... not necessarily the volume drunk since our immune system and the acidity of our stomachs are able to respond to low-level contamination.
Fifth, about 2/3 of those infected have no symptoms (e.g., gas; diarrhea; foul-smelling, floating, greasy feces; abdominal discomfort; cramps or swelling; loss of appetite; nausea; and/or vomiting). The American Medical Association’s findings state that when symptoms do occur, they may begin as soon as one to three days after the parasite has entered the body. Even acute giardiasis usually clears up without treatment, [but the vector (infected individual) spreads the Protist everywhere they go, and will be quite miserable in the meantime].
Sixth, you mentioned that “concentrations for markers are beyond the limits of current technology.” They most certainly are not, and the tests are relatively easy. It was correct that Salmonella tiphimurium is not a major pathogenic source in North American wilderness waters. It is more an issue within the poultry industry, but unrefrigerated poultry on a hunting trip is a recipe for disaster.
Seventh, “latest studies demonstrated that you’d have to drink some 7 liters of the stuff to get sick with an infestation.” It sounds like a newspaper reporter that conducted the metanalysis to which you’re referring because it doesn’t sound like advice from a scientist who works in the field of parasitology, virology, epidemiology, or microbiology. It’s simply inaccurate due to the concentration issue that I already mentioned. I imagine it was hard for the source’s source you cited to find a very large sample size of volunteers who were willing to submit to this giardia experiment, knowing that the researcher would have been looking for the threshold limit that induces Giardiasis. Also, reread the fourth point.
Eighth, you mentioned that “most wilderness waters contain harmless top-water flora and are merely just as much a part of the food chain as fish.” The inference is that anything in the food chain/web is okay to eat. However, I’ve actually seen a live trichina parasite in one of my sources of drinking water. It would be completely harmless to a fish because fish aren’t viable hosts, but I sure wouldn’t want to eat one!
Ninth, to state that “Medicine is now showing “evidence-based” that the existing practices of universally treating wilderness water is supported on deficient or incorrectly interpreted information” is simply misleading. Prodigious empirical evidence exists showing the cause and effect relationship between pathogenic concentrations (and in some cases, presence) and onset of disease whether one is in Chicago or Chilikandrotna. Moreover, pathogenic concentration levels fluctuate from season to season, year to year, stream to stream, location within a given stream, and so on. They’re quite dynamic, so it would be pointless to attempt to survey each remote watershed. Decisions should be based on risk analysis.
I've personally tested Anchorage/MatSu streams as an undergrad that had fecal coliform levels way above federal standards for both potable and recreational water. The question of whether fecal coliform concentrations increase in the spring as they’re washed into streams or become diluted as melt water increases water volume was the focus of past research I conducted as an undergrad. Spring is a particularly notorious time for high coliform concentrations because many animals concentrate and defecate along waterways during the winter. When breakup comes, the melting snow washes feces and fecal coliforms into the waterway. Since bacterial reproduction is exponential, their concentration virtually explodes in short order, sending levels through the roof.
Once again, this isn’t meant to be a personal attack, but the source you chose to quote wasn’t particularly knowledgeable and cause people to make poor decisions and suffer needlessly.
Previous: Evidence Based - concerning Wilderness H2O Brian Richardson Jan 06 2005
Next: Water problems as I see them Michael Strahan Jan 07 2005
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