Regarding treatment, the manual says, «Flagyl ™ (metronidazole) is about 65 % effective» (in removing cysts from feces) and if administered «for 3 days, effectively removes giardia cysts from feces of dogs; no side effects are reported.» (siriusdog.com)
These egg packets then pass in the feces of the dog or cat.» (tulsapetsmagazine.com)
This means your pup can get it from eating the feces of another dog, playing or habiting in the same area as an infected dog, or drinking water from an outdoor puddle that happens to have come in contact with infected feces. (zippivet.com)