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Giardia is killed by common disinfectants such as quaternary ammonium compounds in kennels and on hard surfaces. Chlorine (bleach) is effective at higher concentrations (1:32 part dilution). Drying and heat also kill cysts.
A study in Norway showed that the parasite cysts died during the winter in that country. Shear forces resulting from freezing thaw cycles were part of the reason. However, they can survive moderate temperatures with some freezing.
The cyst dies in dry hot environments, but is very difficult to kill in gardens and lawns where the soil is moist and the vegetation protects the cysts from direct sunlight.
Picking up feces helps reduce the level of contamination. There is a vaccine against Giardia that reduces shedding of cysts, which helps reduce environmental contamination.
Let me know if you have follow up questions.
I have not found a lot of studies on survival of cysts in the environment in terms of time vs temperature with the exception of the Norwegian one. Most of the concern is about purifying drinking water, which is the major risk.
Giardia cysts can survive for 2 months in cold-wet environments. The snow won't kill them, but most will die if we have freezing at night and warmer during the day. It's the mechanical action of freezing and thawing that destroys them.
They do not survive well in hot temperatures or in dry environments. If you don't have streams or ponds on your property, your pup should be OK. Most infections are from drinking contaminated water. Lawns need to be heavily contaminated to be a major risk.
Panacur doesn't always clear dogs. Other treatments include metronidazole (clears 60-75% of infections in dogs). and Drontal Plus. Also give your guy a bath to get lingering cysts off his body.
You can get this disease also. Keep up on hand washing!