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Giardia is a single-celled parasite that lives in a dog's small intestine and causes diarrhea. Most infected dogs have no signs at all, and the ones that do usually have soft or watery stool that comes and goes.1,2 We see many cases here in Kitchener.
Key Takeaways
Call us if your dog's diarrhea isn't going away, or if your dog is also vomiting, tired or off food. Puppies are more likely to get sick from Giardia, and diarrhea can lead to dehydration.3 Call us at (519) 896-0532, or use our emergency page after hours.
Giardia is a protozoan, a single-celled parasite. It isn't a virus, a worm or a bacterium. It lives in the small intestine and has two stages: an active form that attaches to the gut lining, and a tough-shelled cyst that passes out in stool and spreads the infection.1,2 The damage to the gut lining leads to poor digestion and absorption, which brings on the diarrhea.1
Giardia is common. A national Canadian study found it in 3.5% of dogs, and in 5.5% of dogs under a year old. Stool tests miss some infections, so the true numbers are probably higher.2
Dogs get Giardia by swallowing cysts. Cysts are infective the moment they leave a dog in stool, and as few as 10 can start an infection.1,2
The usual routes are stool from another dog, contaminated water or food, soil, and licking their own coat or paws after contact with stool or a dirty surface.1,3 Standing water, creeks, ponds and lakes are common sources.3 Cysts last weeks to months in cool, moist soil or water, and they clear faster in warm, dry, sunny spots.2,3
Giardia is more common in shelters, breeding facilities and kennels, and among dogs that visit dog parks. In one study, 24.7% of dogs attending urban parks in Calgary had it.1 Crowded groups are a particular problem for puppies and stressed dogs.2
Most dogs with Giardia show nothing. When signs do appear, diarrhea is the main one. The stool can be watery, soft or mucousy and foul-smelling, and the diarrhea can be sudden, constant or on and off.1,2 Gas and vomiting can come with it. In severe cases a dog may also be lethargic, stop eating or lose weight.1
Signs usually start one to two weeks after a dog swallows cysts. Without treatment they may fade within a couple of weeks, or the diarrhea may turn chronic or keep coming back.2 Puppies and young dogs are the most likely to get sick.2,3
A dog doesn't need diarrhea to spread Giardia. Dogs with no signs still shed cysts and can infect other dogs, and a dog that has stopped having diarrhea can keep shedding.2,3
Many things cause diarrhea, which is why a stool test comes first.3 Stress colitis is one of them. If you see blood, read about blood in your dog's stool.
Your vet starts with a stool sample and looks for cysts, the moving parasite itself, or Giardia proteins (antigen), often with more than one test.1,2
Many clinics run an antigen test on site, and the SNAP test shown here is the one we use.2
One negative stool test doesn't rule Giardia out. Dogs shed cysts on and off, so your vet may ask for samples on several alternating days.1,2 Fresh stool gives the best result, so bring the most recent sample you can.1
The Companion Animal Parasite Council (CAPC) recommends a centrifugal flotation for healthy dogs entering boarding, grooming or daycare.1
| Test | What it finds | Limits |
|---|---|---|
| Fecal flotation with centrifugation | Cysts | Cysts are shed on and off, and a reader with little experience can miss them.1,2 |
| Direct smear | The moving parasite, in fresh diarrheic stool | Needs a fresh sample, ideally under 30 minutes old.1 |
| Antigen test (ELISA), such as SNAP | Giardia proteins in stool | Can stay positive after treatment, so it isn't used to judge whether treatment worked.1 |
| PCR | Giardia DNA, and with some tests whether the type can infect people | Done at an outside lab. Can stay positive after treatment.1 |
Giardia can also be mistaken for inflammatory bowel disease, so ruling it out is a good place to start when a dog has ongoing diarrhea.
Giardia treatment is a short course of prescription medication, plus a bath and a clean-up. No over-the-counter product treats it.3 Fenbendazole and metronidazole are the two common choices, and some dogs get both.2 The Western College of Veterinary Medicine notes that no drug is approved for Giardia in dogs in Canada, so vets prescribe them off-label.2
| Drug | Usual course | Notes |
|---|---|---|
| Fenbendazole | 3 to 5 days | Also treats common intestinal worms. Approved for Giardia in dogs in Europe.1 Dosing is in our fenbendazole post. |
| Metronidazole | 5 to 8 days | The most commonly used drug for Giardia.1 Side effects and dosing are in our metronidazole post. |
Treatment has four steps:
A dog with bad diarrhea may also need supportive care.2 If you have other pets, tell your vet even if they look healthy. Some are infected and spreading Giardia without signs, and your vet may treat them too.3
A dog with no signs may not need treatment. That is the majority opinion of the CAPC board.1 Vets do treat these dogs when the dog lives with a vulnerable or immunocompromised person or pet, or when the strain can infect people.1 Your vet decides with you, based on your dog's lifestyle, household and treatment history.1
Parasites that survive the course can rebound, and dogs get reinfected from a contaminated yard or from other dogs, which is common where contamination is heavy.1,2 Other causes include a weak immune system and drug resistance.1 Treatment sometimes has to be repeated.2
The goal of treatment is fewer signs and less contamination of the environment, not guaranteed elimination. So vets don't usually retest a dog whose diarrhea has cleared.2
Rarely. People mostly catch Giardia from other people, and from contaminated water or food.1,2 The Centers for Disease Control and Prevention says you are unlikely to get it from a dog or cat, because the type that makes people sick is usually not the type that infects dogs and cats.3
The risk isn't zero. Some types infect both people and dogs, and routine tests can't tell which type your dog has, so the Western College of Veterinary Medicine advises treating every case as potentially infectious to people.2 People with weakened immune systems or underlying illness should limit contact with an infected dog.1
If you and your dog both have Giardia, that doesn't mean your dog gave it to you.1 Wash your hands after touching your dog, its stool, food or supplies, and wear gloves when you garden.3 If you develop diarrhea or stomach upset after contact with an infected pet, see your doctor.1
You can't remove Giardia from a yard, but you can cut down how many cysts your dog meets.3
Cysts die from heat above 60°C, from drying, from sunlight (UV light), and from bleach, quaternary ammonium or hydrogen peroxide products.2 Steam cleaning works too.1
If your dog has diarrhea that isn't going away, bring a fresh stool sample and call us at (519) 896-0532, or send us a message.
Rarely. People mostly catch Giardia from other people and from contaminated water or food, and the type that infects people is usually not the type that infects dogs. Wash your hands after touching your dog, its stool, food or supplies, and see your doctor if you get diarrhea or stomach upset after contact with an infected pet.
Usually one to two weeks. Many infected dogs never show signs at all, and they can still shed cysts and infect other dogs.
Not always. The majority opinion of the Companion Animal Parasite Council board is that dogs with no signs may not need treatment. Vets do treat them when the dog lives with a vulnerable or immunocompromised person or pet, or when the strain can infect people. Your vet will decide with you.
Common reasons are reinfection from a contaminated yard or from other dogs, and parasites that survived the course. A weak immune system or drug resistance can also be behind it. Treatment sometimes has to be repeated, along with a bath and a thorough clean-up.
No. Dogs shed cysts on and off, so a single sample can miss them. Your vet may test several samples on alternating days, or combine a stool flotation with an antigen test or PCR.
No. Only a vet can prescribe the drugs used for Giardia, usually fenbendazole or metronidazole, and no approved over-the-counter medication treats it.
No. While a dog has diarrhea or is on treatment, keep it away from dog parks and public trails, because cysts in stool spread the infection. Pick up and bag stool every day.
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