Giardia is a protozoal intestinal parasite of dogs and cats. It is also the most common intestinal parasite in humans in North America. It is considered a zoonotic disease, meaning that there is potential for people to pick up the infection from animals.

Giardia is transmitted by the oral ingestion of cysts, either from feces or contaminated water sources. The cysts are extremely resistant to many types of disinfectants, other than bleach. The most common sign of infection is diarrhea.