I hope I was not sounding impatient.  I felt puzzled, not impatient.
Giardia could be transmitted by what is relatively delicately called
in medical jargon the "oral-fecal route".  It is also transmitted from
beavers in western North America who poop into the rivers and then
people drink the water, unboiled, because western rivers look so
clean.  The infection is known as beaver fever, though fever is pretty
uncommon with this infection.

Jack Newman, MD, FRCPC