Giardia is commonly found in the water supply, with the whether the way it is , I can see how it would raise it's ugly head again, also can be found on fruits and veggies..
The suggestions are...
use bottled spring water for your gliders,
be sure you wash your fresh fruits and veggies real well,
when cleaning the water bottle be sure you get inside the tube and under the rubber washer. A real long pipe cleaner does work well there.
Alongside these, Fecals are the best prevention
Take your glider feces in for regular fecal tests, suggested every three months, if they find ANY, have them treat them. too many
vets thinks one shell isn't enough to worry about.
as far as symptoms, it is basically a symptomatic, till it becomes a problem with the exceptions of the fecal tests.
but after wards, weight loss, lethargy, diarrhea, dehydration, just basically the feeling something isn't right. Most of the time, they will hide their symptoms till it is too late. You have to be in tune with your gliders health.