Dogs Get Giardia by Swallowing It—Often Without Eating Poop

Dogs get Giardia by swallowing microscopic parasite cysts shed in infected feces. They do not have to visibly eat poop. Cysts can reach a dog’s mouth from contaminated water, soil, grass, fur, paws, food or objects.

This is called fecal–oral transmission: cysts leave an infected animal in stool and are then swallowed by another animal, directly or through the environment. The cysts are immediately infectious and can survive for weeks or months in cool, damp conditions, according to the Merck Veterinary Manual.

Common ways dogs are exposed

A dog may swallow Giardia after:

• drinking from a contaminated puddle, pond, creek or shared water source;
• licking muddy paws or fur after playing on contaminated ground;
• sniffing contaminated stool or soil and then licking the nose;
• eating feces or feces-contaminated food;
• using a contaminated bowl, toy, crate or other object;
• having close contact with infected dogs in a kennel, shelter, breeding facility, daycare or dog park.

Walking past an infected dog is not enough by itself: the parasite must reach the mouth. However, close-contact settings create more opportunities for stool, wet ground, paws and shared objects to complete that route. Infection is more common among dogs in shelters, breeding facilities and kennels, and studies have found higher prevalence among dogs that visit dog parks, according to the Companion Animal Parasite Council.

Can dogs get Giardia from puddles?

Yes. Outdoor water can carry Giardia if infected feces have contaminated it. Clear-looking water is not necessarily safe because the cysts are microscopic. The risk is not limited to wilderness streams; contaminated standing water around a yard or communal dog area may also create an exposure.

Can one dog pass Giardia to another?

Yes, but the route is still fecal–oral. An infected dog may leave cysts on the ground, its rear end, fur, paws or shared objects. Another dog can swallow them while licking or grooming. A dog can be infected and shed Giardia without having diarrhea, so a healthy-looking playmate does not rule out exposure. The CDC’s pet guidance confirms that animals can spread the parasite even when they look healthy.

Why can Giardia seem to come back?

A treated dog can be exposed again if cysts remain on its coat or in its environment. Reinfection is more plausible when stool is not collected promptly, the dog drinks outdoor water, or contaminated bowls, bedding and crates are not cleaned. Cyst shedding can also be intermittent, which may complicate testing and make an unresolved infection look like a new one.

Exposure does not prove infection

Many infected dogs have no symptoms. When illness occurs, diarrhea may be sudden, intermittent or persistent. Stool may be soft, foul-smelling, pale, greasy-looking or contain mucus. Gas, abdominal discomfort, reduced appetite and weight loss can occur, and puppies are more likely than adult dogs to become sick.

These signs are not unique to Giardia. Diet changes, other parasites, infections, toxins and intestinal disease can look similar. Use your dog’s behavior and other warning signs—not stool appearance alone—to judge urgency; see why dogs get diarrhea and when to act.

A veterinarian may test stool for Giardia cysts or antigens. Because an infected dog may not shed cysts in every bowel movement, multiple samples or more than one type of test may be needed. Ask the clinic whether to bring a stool sample and how it should be collected. Do not use a leftover or over-the-counter dewormer without veterinary direction; the CDC states that no approved over-the-counter Giardia medication is available for pets.

Watch, call a vet or go now?

Watch closely: A healthy adult dog had a possible exposure but remains energetic, eats and drinks normally, and has normal stool. Prevent another exposure and monitor. Exposure alone does not confirm infection.

Call or book a vet: Contact your veterinarian if diarrhea persists or keeps returning, or if your dog has reduced appetite or unexplained weight loss. Call sooner for a puppy, senior dog or dog with another health condition. Mention recent boarding, daycare, dog-park visits, feces eating or untreated-water exposure.

Call promptly if you see blood in the stool or repeated vomiting or diarrhea. These signs have several possible causes and should not be assumed to be Giardia.

Seek urgent care now: Go promptly for collapse, marked weakness or reduced responsiveness, a swollen or painful abdomen, repeated attempts to vomit without producing anything, inability to keep water down, or severe bloody diarrhea with vomiting or weakness. Dehydration is a particular concern in puppies and small dogs. VCA Animal Hospitals advises urgent veterinary contact for persistent vomiting or diarrhea, blood, weakness or reduced responsiveness.

Reduce spread and reinfection

• Pick up stool promptly, bag it and throw it away.
• Prevent drinking from puddles, ponds, creeks and communal containers.
• Wash your hands after handling stool, pet supplies or a soiled dog.
• Clean bowls, toys, bedding, crates and floors while a dog is infected, following veterinary instructions.
• Bathe a diagnosed dog as directed to remove fecal material from the coat.
• Keep a dog with diarrhea away from dog parks, public trails and communal water.
• Tell your veterinarian about other dogs or cats in the home, even if they seem healthy.

Do not pour bleach or other disinfectants onto the yard. The CDC says these products do not eliminate Giardia from soil or grass; remove feces and standing water instead.

People are unlikely to catch Giardia from a dog or cat because the types that usually infect people differ from those commonly found in pets. The risk is not zero, so handwashing and careful stool cleanup still matter, especially if someone in the household has a weakened immune system (CDC).