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Giardia in Dogs and Cats: Diarrhea, Testing and Treatment

Giardia is a common gut parasite that can cause diarrhea. How pets catch it, testing, treatment, bathing and cleaning to stop reinfection, and the risk to people.

Updated October 2026 · 6 min read · By the Hushku editorial team · 1 sources

Short answer

Giardia is a microscopic intestinal parasite picked up by swallowing cysts from contaminated water, soil or faeces. Many infected pets have no signs; others get soft, smelly diarrhea that can come and go. It's diagnosed with stool tests and treated with fenbendazole and/or metronidazole, plus a bath at the end of treatment and prompt poop pick-up to prevent reinfection.

Key facts

Giardia was found in about 5.7% of dog and 4.8% of cat stool samples in a 2023 US survey.
Cysts are infective as soon as they're passed.
Bathe your pet on the last day of treatment to remove cysts.
Spread from pets to people hasn't been conclusively shown in North America.

Definition

Giardiasis is an infection of the small intestine with Giardia duodenalis, a single-celled protozoan parasite spread by the faecal-oral route.

Infected animals pass cysts in their faeces, and the Companion Animal Parasite Council notes these cysts are infective as soon as they're passed. Pets swallow them from contaminated water (puddles, ponds, streams), food, objects, or while grooming.

Giardia is common: a 2023 nationwide US survey cited by CAPC found it in 5.72% of dog stool samples and 4.82% of cat samples, with higher rates in shelters, kennels and dog parks. Puppies and kittens are most likely to show signs.

Shedding is intermittent, so a single negative test doesn't always rule it out; your vet may test more than once.

Signs and symptoms

Often none
Soft, pale, greasy or foul-smelling diarrhea, sometimes with mucus
Diarrhea that comes and goes
Gas and an upset stomach
Weight loss or poor growth in puppies and kittens
Occasionally vomiting or lethargy

Causes and risk factors

Drinking from puddles, ponds and streams
Contact with infected faeces at parks, kennels, daycare and shelters
Grooming contaminated fur
Reinfection from the pet's own environment

Treatment

Fenbendazole, metronidazole or both, as prescribed by your vet
A bath with pet shampoo on the last day of treatment to remove cysts from the coat
Picking up faeces straight away and disposing of it in household waste
A highly digestible diet while the gut recovers
Retesting if signs continue

Prevention

Pick up after your dog promptly
Provide fresh water on walks so your dog doesn't drink from puddles
Clean and dry bowls, bedding and hard surfaces regularly
Clean litter boxes daily

Does a pet without signs need treatment?

CAPC's majority view is that pets with Giardia but no diarrhea may not need treatment, but treatment should be considered for pets living with vulnerable people or animals, or infected with a type that can affect people. Your vet will help you decide.

Can people catch Giardia from pets?

CAPC notes that spread from dogs or cats to people hasn't been conclusively shown in North America, and the types that infect pets are mostly different from those that commonly infect people. People with weakened immune systems should still take care: wash hands after handling pets and picking up faeces.

Cleaning up

Cysts are killed by drying and by many disinfectants. Clean hard surfaces with detergent, rinse, then dry thoroughly. Wash bedding hot. Grass and soil can't be disinfected, so prompt poop pick-up is the most important step.

Free tools for this

Dog and cat symptom checker

Sources

Companion Animal Parasite Council: Giardia

We check guides against veterinary sources and update them when guidance changes. How we write and review.

Questions.

Why does my dog keep getting Giardia?

Usually because of reinfection from the environment or other pets, or because cysts on the coat are swallowed during grooming. Bathing at the end of treatment and strict clean-up help.

Can my dog go to daycare with Giardia?

Keep your dog away from other dogs until treatment is finished and diarrhea has resolved, and check your daycare's policy.

Is there a Giardia vaccine?

Not one that's recommended. Hygiene and prompt treatment of sick pets are the main controls.