Your dog can get giardiasis -- the illness caused by Giardia -- from many sources, but Lucky is unlikely to become infected from his food. Lucky could get giardiasis only if his dog food is contaminated with feces from an infected mammal. He is more likely to be exposed to Giardia from other infected dogs.
Sources of Infection
Giardia are microscopic intestinal parasites. Dogs become infected with these protozoans when they ingest infective cysts. Infected animals shed these cysts in their feces, contaminating food, water, land or physical objects. Dogs are commonly infected by drinking contaminated water, such as from standing water puddles, ponds and streams. Dogs can be infected by coming into direct contact with another dog’s feces, such as when rolling in dirt at a dog park. Dogs ingest cysts by licking their paws, bodies or contaminated toys. While any dog can be infected with Giardia, the Centers for Disease Control and Prevention states that puppies are more likely to become infected.