“Most giardia infections are asymptomatic, meaning there are no obvious signs your pet is infected. When symptoms are present, the most common is diarrhea, which can be acute, chronic or it can come and go.”

“Due to the intermittent nature of loose stools associated with giardia, many people assume the dog got into something he shouldn't have, or had a meal that didn't agree with him. Consequently, many cases of giardia go undiagnosed.”

“I recommend an ELISA or PCR test for giardia for any pet with a history of GI issues. A fecal ELISA or PCR test is preferable to a fecal flotation test because it checks for the presence of giardia antigens. A fecal float only detects giardia cysts, which may or may not be in the particular stool sample being tested.”

https://healthypets.mercola.com/sites/healthypets/archive/2018/01/14/giardia-in-pets.aspx