Giardia is tiny, one - celled parsitic life form.It is injested from contaminated water or contaminated feces. That's why is is common to pick it up at the park, vet office, or a kennel. Some dogs can carry giardia and show no symptoms so they keep passing it around. Giardia interferes with the absorption of food nutrients and causes diarrhea or soft, light-colored, greasy stools. It also may cause mild anemia and it increase in white blood cells. Hope this helps.