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)
Giardia can be treated with the prescription drug fenbendazole from your veterinarian which effectively removes Giardia cysts from the feces of dogs. (thesprucepets.com)
In areas where there giardia is commonly found (such as areas with natural lakes and other waterways), approximately 6 % to 11 % of dogs shed giardia cysts. (dog-health-guide.org)