Giardia is a common parasitic infection that can cause diarrhea in dogs. It is caused by an intestinal parasite called Giardia, which can be found in feces-contaminated soil, food, and water. Giardia has two forms: trophozoites, which live in the intestines of infected dogs, and cysts, which are trophozoites protected by an outer shell and that get shed in the dog’s stool. Dogs get Giardia from ingesting feces-contaminated water, soil, food, or objects. Some dogs infected with Giardia may not show any signs of infection, but younger dogs or dogs with weakened immune systems are more likely to experience symptoms. The most common symptom of an active Giardia infection is watery diarrhea, which may be greenish or yellow in color, or it might be brown, but it is always going to be liquid. There may sometimes be blood present in a dog’s stool as a result of Giardia as well. Infected dogs tend to have excess mucus in their feces, and vomiting may occur in some cases.

It is very easy for dogs to reinfect themselves with Giardia, so successful treatment relies on effective anti-parasitic medications, cleaning, and managing the surrounding environment — both indoors and outdoors. The most common drugs used to kill Giardia are metronidazole and fenbendazole. Although Giardia flare-ups may come and go on their own, the parasite itself must be treated with medication. Giardia is not a fatal condition, except in very young puppies or very old senior dogs. In humans, Giardia is a common cause of diarrhea, but dog Giardia is not generally considered to spread from animals to humans. However, it is possible to be infected and have no signs or symptoms of illness. Regardless, washing hands thoroughly with soap and water after handling pets or infected feces is always important.