Why do many backpackers ignore the risk of worms or worm eggs in their water? Chemical treatments and UV light aren't effective against them. It appears that raccoon roundworm is very prevalent in raccoons, and one site even implies that the eggs are resistant to boiling water:

"To destroy the egg you must use boiling lye or propane torching."
http://www.mass.gov/dfwele/dfw/wildlife/diseases/raccoon_roundworm.htm

Here's one of the possible effects:
http://www.cbsnews.com/video/watch/?id=6888137n

I've drunk untreated water before, but I think I'm switching to drinking only filtered water.

Of course, it's really a question of how likely it is that the eggs are actually in the water. I might risk a long bout of diarrhea, but I'm not willing to put my brain or other essential organs at risk.

Edited by AndyF on 08/29/2011 13:29:13 MDT.

This is yet another reason for me to justify the weight of my filter. Bleh.

but at least out west for us we rarely treat even, let alone filter - probably 90% of the water we drink is coming off of alpine snow slopes fresh from melting within a few hours or else coming straight out of the ground from snow melt above and thus ground-filtered. we treat from lakes though. if/when we ever get sick sick from water, we'll probably change our behavior but years going and no problems so..

It's called baylisascariasis (caused by Baylisascaris procyonis, a raccoon roundworm). It's really, really horrible, but also really quite uncommon - per the CDC, there have been only 13 well-documented cases of pretty bad central nervous system involvement reported... It is usually contracted by children that are playing with or eating dirt contaminated with raccoon f*ces (containing the eggs) in raccoon-heavy areas (often their own back yards).

One for the "too much information" file, from your friendly medical microbiologist/pathologist backpacker...

Edit to add: Not sure how this guy got it, but it might be prudent to filter if gathering water from areas with big raccoon populations...

Edited by kushbaby on 08/30/2011 23:39:45 MDT.

It's ignored due to the low risk of this occurring in general - there are many competing risks and there are many others that have a much higher probability. It's like worrying about being attacked by a shark while swimming but ignoring the fact your more likely to drown or being in a plane crash while ignoring the hazards associated with driving your vehicle everyday. Concerned about cancer even though at most age groups your much more likely to die from a cardiovascular event. Very dramatic terrifying events, but unlikely to actually occur relative to other much more common risks.

However, the risk is not constant -this may be an issue with significant raccoon populations and may warrant precautionary measures. If I'm in New Jersey hiking I'm being cautious of deer ticks due to them being a lyme disease vector and the risk is real there per the epidemiology studies. Here in WA though, lyme disease isn't an issue so why worry about it?

Where you hike are there significant populations of raccoons?

Edited by rmkrause on 08/31/2011 00:06:16 MDT.

In the adult, I'd bet inhalation would be more common. Raccoons tend to live in attics of older homes so being in the attic without a proper mask would be one way on contracting the bug.

@Kristin: With it being so prevalent in raccoons, and the eggs being so hardy, I wonder if baylisascariasis isn't more common. Maybe it just rarely causes obvious problems? Maybe it commonly eats away at the part of the left parietal cerebral cortex which causes people to fail to realize they don't really need to carry a heavy pack? :)

@Ryan: I agree. There are raccoons in the areas I hike (Appalachians and foothills), although I wouldn't say there are significant numbers. I guess I just don't like the Russian roulette approach to water safety. The water is most likely clean, but there might be a raccoon latrine just upstream too.

@John: True, good point.

@Matt: Right, different situation in the high mountains... unless maybe mountain goats and marmots can be carriers of any dangerous worms?

@Laurie: My perspective exactly. The risk is enough to make me choose filtration over chemical or UV. I don't like adding chemicals to the water anyway, and I'm skeptical of relying on electronics with batteries. The admittedly small risk of baylisascariasis or even a less dangerous worm is enough to sway me toward filters over other methods. Btw, I just got a Sawyer Squeeze filter which is 4.5 oz (wet weight, including dirty bag). That's heavier than chemicals, but around the same as UV, and tastes better than chemicals.

What size filter is needed for keeping eggs out?

If they are big like Cholera, then a couple of layers it tight woven cloth would be
a possible filter. Then the water could be otherwise treated.

"Baylisascaris procyonis eggs are 80-85 µm by 65-70 µm in size"

http://www.dpd.cdc.gov/DPDx/html/ImageLibrary/A-F/Baylisascariasis/body_Baylisascariasis_il1.htm

It sounds like a material with a 40 µm pore size would be adequate, to be on the safe side. What type of material has a pore size <= 40 µm?

The Steripen prefilters are 40x40 µm, as one that comes to mind. Pretty coarse, actually.

Cheers,

Rick

"An old cotton sari, folded, creates a smaller effective mesh size (approximately 20-μm). This should be small enough to remove all zooplankton, most phytoplankton, and thus a large proportion of the cholera in the water (99%, according to laboratory studies). However, the nylon net with the larger mesh size was found to be "almost equally effective."[2]"

http://en.wikipedia.org/wiki/Cloth_filter


--

What is the pore size of a bandana?

about 100μm

"Do Bandanas Provide Protection?
Bandanas have been used by wildland firefighters for decades, however, they should not be considered a viable
choice for respiratory protection. Scanning electron microscope photographs of both new and used bandanas have
shown openings (pore sizes) within the fabric that exceed 100 μm in length and width, which allow particulate matter
to pass freely through the fabric (Reh and others 1994)."

www.fs.fed.us/eng/pubs/pdf/hi_res/07511301hi.pdf

--

So it looks like a tight woven cloth would work, but it would need to be tighter than
a common bandana and it would need to be folded at least once.

@Andy: Lower frequency of clinically apparent disease may be a dose-related effect. A number of the case reports I've read have involved children with developmental disorders or autism who eat a lot of the stuff... Do note that humans are not part of the normal life cycle of this worm, but are "incidental hosts" (which fits with a low prevalence). EDIT TO ADD: I like the idea that this explains why some people don't realize they don't have to carry a heavy pack. Unfortunately, that would mean that I was infected for many years and suddenly got better... :D

@John: The eggs are too large to be inhaled and cause infection through the pulmonary route. Andy beat me to it in posting the size of the eggs, but they're quite large...

Edited by kushbaby on 09/01/2011 16:49:51 MDT.

"An old cotton sari, folded, creates a smaller effective mesh size (approximately 20-μm). This should be small enough to remove all zooplankton, most phytoplankton, and thus a large proportion of the cholera in the water (99%, according to laboratory studies)."

I'm skeptical of this, given that the size of a cholera bacterium is 1-5 microns.

@Kristin: That makes sense I guess. The more worms there are, the more likely they'll burrow into something important. Ha ha! Good point about the heavy pack part! :D

Tom, I too am skeptical. A micron is pretty darn tiny.

In the last year or two there have been a lot of scary articles about this in the papers - but it is still pretty rare overall.

IMO you have more to fear with gardening bare handed in raccoon areas (where we live we have plenty of them loitering around due to a healthy population of feral cats). Anyhow....the whole point is that you can pick them up doing normal activities - but that I agree with other posters here: in the West up high you never see coons. Coons like the coast where the living is easy and the food is easy to get - for example you see them on the coastal strip as they looooovvvveeee shellfish. But outside of there and car campgrounds I have never seen one above 1K in elevation. Coons are opportunistic critters and like life to be easy. Alpine isn't easy. And more so coming from experience (I lived on an Island for 1 1/2 decades) they like to stay put once they find a gravy train - and live there, breed there and breed some more. In other words, right under your bedroom since you live right above a lovely cove of water.

I hate it when I finally get comfortable with my water treatment and someone makes me question if I'm doing enough all over again. ;)

Yup. You can get worms from going barefoot too.

There are raccoons around Lake Union in the center of Seattle. I live a few miles north and we have them all over, along with beaver, eagles, hawks, great blue herons, opossum and coyotes-- and even an occasional black bear or cougar.

+1 on the raccoons on the coast. Bear cans are required on the Olympic Beaches. We haven't seen a bear in over 20 years, but the raccoons are numerous and the cans help there. The lil' monsters will come right up to your camp in broad daylight.

"I'm skeptical of this, given that the size of a cholera bacterium is 1-5 microns."

You filter out the host and the host's food, which are much larger. When you reduce the
total load (number of things being ingested) you get reduced, sometimes greatly reduced,
infection.


"The disease is caused by the bacterium V. cholerae that attaches itself to tiny, water-borne animals called copepods. The bacteria collect around the mouths and on the egg casings of female copepods, said Colwell, and the bacteria and copepods seem to have developed a mutually beneficial relationship. The animals offer transportation to the bacteria, which in turn help rupture the egg casings of the females so that they can disperse their ova."

http://www.hsph.harvard.edu/ats/Apr28/

Reduced load applies to Giardia too. If you only ingest one or two cysts you are unlikely
to get the disease. That's why drinking from huge glacial rivers and fresh sierra snow pack is of little concern due to dilution.

As posted on the recent gun thread and updated to this thread.

"The need to carry (a water filter) in the city or the wilderness just reaks of fear. I realize others see it different, but I see it as a sign of fear."