From: tut@cairo.Eng.Sun.COM (Bill "Bill" Tuthill)
Newsgroups: rec.backcountry
Subject: Rickettsia, Giardia, Filters
Date: 10 Sep 92 22:10:32 GMT
Organization: Sun Microsystems Inc., Mountain View, CA
NNTP-Posting-Host: cairo

Dave Graham (deg2@crux2.cit.cornell.edu) asked me to post this
information, since he can't.

Rickettsia:
***********
	Just to set the record straight, Rickettsia rickettsi, the
microorganism responsible for Rocky Mountain spotted fever (RMSF)
is an "obligate intracellular parasite".  It has RNA, DNA, a cell
wall and a cytoplasmic membrane ("trilamellar structures"). 
Approximately 0.5 to 2.0 um (microns) in length by 0.2 to 0.6 um
in width, it certainly could pose a problem to many filter systems. 
Every year, this [genus] seems more like bacteria...

	Anyhow, RMSF is supposedly transmitted by ixodid ticks in
the Western Hemisphere.  Rickettsia are excreted in the saliva and
feces of its vectors.  These vectors range from ticks to rabbits to
dogs.  In guinea pigs, there is a high susceptibility to infection,
causing scrotal swelling and necrosis.  However, in mice the
susceptibility is low.  (NB. in both these cases, the R. rickettsi
was probably injected directly into the bloodstream.)  Similar, but
less severe cousins pop up across the rest of the world.

-Info from O'Leary, W.M. 1989. Practical Handbook of Microbiology.
CRC Press: Boston.

	Although anything's possible, I wouldn't worry too much about
oral infection via water (barring cuts or wounds in the mouth).
Ticks are far more problematic in transmission and also carry Lyme
disease, etc.  Still, there are plenty of other reasons to treat
your water to make it potable.  Don't quote me on this speculation.

Giardia:
********
	Giardia lamblia are protozoans (diplomonads) which have a
wonderfully silly expression on their (faces) when viewed under the
microscope.  About 10 um, these curious micro-organisms can pack
quite a punch in your gastrointestinal tract.  While I'm generally
unfamiliar with the testing procedure and its accuracy (or lack
thereof) I've heard it involves dental floss or fishing line
(depending on which way you look at it).  You're the fish and the
bait doesn't taste too great going down or coming back up.

-Info on Giardia morphology from Sleigh, M. 1989.  Protozoa and
Other Protists.  Cambridge University Press: Cambridge.

	If you have any kind of a reasonable filter (pores smaller
than 10 um) you should be able to avoid Giardia.  In any case,
popular wisdom seems to be to avoid heavily beaver infested areas,
very cold streams, etc.

	I have a 1982 paper here, "Inactivation of Giardia Cysts by
Chlorine." The long and the short of it is that "a free residual
chlorine concentration of 2.5 mg/L" at 5 deg C killed off about 80%
of the cysts at pH 6 in 10 minutes.  After 60 minutes, 99.6% of the
cysts were killed (still at pH 6).  These values are read off a
graph and describe G. lamblia cysts of symptomatic donors only. 
Asymptomatic donor cysts show only 97% death after 1 hour at pH 6. 
At higher pH values (more basic/alkaline water) the deaths
decreased.

-Info from Rice, E.W., J.C. Hoff, and R.W. Schaefer III. 1982.
"Inactivation of Giardia Cysts by Chlorine."  Appl. Environ.
Microbiol. 43:250-251.

	My best guesses about this data are that a low pH, long
exposure time, and adequate chlorine concentration (you're on your
own here...) are the best bet to chemical treatment.  Your best
bet seems to be filtration, coupled with chemical treatment with
chlorine or iodine, if you're unsure of your filter's status.
The researchers used 0.5 um pores to count the Giardia cysts, so
a 0.2 um pore size should be more than adequate.

Filters:
********
	A word about filters: My advisor (an environmental
microbiologist) said that our laboratory grade filters (Millipore
(TM) and such) have only an AVERAGE pore size of 0.2 to 0.4 um. 
Thus some pores are considerably larger than this, and some less
so.  We try to use 0.2 um (the smallest practical) when we filter
samples.  Of course we're after the bacteria, not the water :-)
Whether this also applies to modern, commercial potable water
filters is up for grabs.  Their figure could be the maximum pore
size, but then again...

Disclaimer: Any information contained herein ought legally to be
considered bunk.  I take no responsibility for anyone's actions or
lack thereof stemming from this information.  Drink at your own
risk.  Enjoy the water, it's free but the filters aren't.