Giardia in Dogs: Signs, Testing and How to Stop Reinfection

What it usually means

Giardia is a single-celled parasite that attaches to the lining of the small intestine and interferes with how a dog absorbs food and water. Dogs catch it by swallowing cysts, the parasite's tough, dormant form, which can survive for months in cool, damp places such as puddles, streams, lawns and kennel runs. According to VCA, an infected dog starts shedding new cysts in its stool about 5 to 12 days after swallowing them, and those cysts are infectious straight away.

That is why giardia spreads so well wherever dogs gather: shelters, breeders, boarding kennels, dog parks and daycare. Puppies, young dogs, and dogs with a weakened immune system are most likely to show illness. Plenty of healthy adult dogs carry it with no symptoms at all and are only found on a routine stool test.

Signs of giardia in dogs

The typical picture is diarrhea that is soft to watery, pale or greenish, greasy or slimy with mucus, and unusually foul smelling. It may start suddenly, or it may linger as on-and-off loose stools for weeks. Some dogs also have gas, vomiting, a dull coat, weight loss or low energy, even while their appetite stays normal.

Giardia is rarely life-threatening in an otherwise healthy dog, but the same signs have many other causes, from diet changes and other worms to parvovirus and inflammatory bowel disease. You cannot tell giardia apart from these at home, so persistent diarrhea always deserves a stool test.

When to call your vet today

Call your vet if your dog's diarrhea lasts more than a day or two, keeps coming back, or has mucus or streaks of blood in it, and bring a fresh stool sample in a sealed bag. Call the same day for any puppy with diarrhea, since young puppies dehydrate quickly and are at risk of more serious infections that look similar at first.

Also call if your dog is losing weight, seems tired, is vomiting as well, or if diarrhea started after drinking from a lake, river or puddle, or after a stay at a kennel or shelter. Mention any recent travel and whether other pets in the house have loose stools too.

When it's an emergency

Go to your vet or the nearest emergency vet immediately if your dog has repeated vomiting and diarrhea and cannot keep water down, if the diarrhea is bloody or black, or if your dog is weak, collapsing, has pale gums or a swollen, painful belly.

An unvaccinated puppy with vomiting and diarrhea needs to be seen urgently, because parvovirus can look similar in the early stages and is far more dangerous. Signs of severe dehydration, such as sunken eyes, dry sticky gums and skin that stays tented when pinched, also need same-day care.

What you can safely do at home

Keep fresh water available at all times and encourage your dog to drink. Pick up poop immediately, bag it and put it in the trash, and keep your dog off shared grass until your vet clears it. Wash your hands after every cleanup, and keep young children away from the yard while it is being cleaned.

Do not give human anti-diarrhea medicine, leftover antibiotics or dewormers you have at home. They may be the wrong treatment, some are harmful to dogs, and they can mask signs your vet needs to see. Ask your vet before changing diet; a bland, easily digested food is often suggested, but the choice should fit your dog.

What the vet will likely check

Giardia cysts are shed on and off, so a single routine stool test can miss them. Your vet may use a special flotation test, a stool antigen test, or look for the moving parasites on a fresh smear, and may ask for samples from more than one day. They will also check for other parasites and assess hydration.

Treatment is antiparasitic medicine your vet prescribes for several days, sometimes repeated or combined if signs persist, plus fluids or other support for dogs that are dehydrated. VCA recommends retesting about two to four weeks after treatment. Your vet may also suggest bathing your dog at the end of treatment to wash cysts off the coat, especially around the rear, and treating other dogs in the house at the same time.

Cleanup and prevention

Reinfection is the main reason giardia seems to come back. Remove poop from the yard straight away, wash bedding and toys in hot water, and clean hard floors, crates and bowls with a disinfectant your vet recommends; dilute bleach is effective on surfaces it will not damage. Giardia cysts dislike drying, so let cleaned areas dry thoroughly before your dog returns.

Prevent new infections by carrying fresh water on hikes so your dog does not drink from streams or puddles, picking up after your dog in public spaces, and quarantining and testing new dogs before they share a yard. On the human side, the CDC says people are unlikely to catch giardia from dogs, because the types dogs carry usually differ from the ones that infect people, but good hand washing is still wise, particularly for anyone with a weakened immune system.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.