Giardia in Cats: Signs, Testing, Treatment and Cleanup

Giardia is a common gut parasite in cats. Some cats get soft, pale, smelly diarrhea that comes and goes; plenty of others carry it with no signs at all. Your vet confirms it with stool tests and chooses the medicine. Your part is the cleanup, because cats easily swallow the parasite again from their own fur and litter box.

The good news for the humans in the house: you are unlikely to catch Giardia from your cat. The harder part is breaking the reinfection loop, and the cleaning routine further down shows how.

What Giardia is

Giardia duodenalis is a single-celled parasite (a protozoan) that lives in the small intestine. It is found worldwide. It has two forms:

• Trophozoite: the active form. It swims in the small intestine and clings to the gut lining with a suction disc. The damage it does there blunts the lining, so food is poorly digested and absorbed. That is where the diarrhea comes from.
• Cyst: the tough, shelled form. Trophozoites turn into cysts as they move toward the colon, and the cysts leave the body in the stool.

Cysts are the problem for owners. They are infective the moment they are passed, and in cool, damp places they can survive for weeks or even months.

How common is it? According to the Companion Animal Parasite Council (CAPC), Giardia turned up in about 10% of US cats tested because they had signs of illness, and in 4.82% of cat stool samples in a 2023 nationwide survey.

How cats catch Giardia

A cat gets infected by swallowing cysts. That can happen through:

• Water, food or objects contaminated with infected stool
• Contaminated soil
• Licking surfaces such as a dirty litter box
• Grooming its own fur, if stool with cysts is stuck to it

That last route is why Giardia is so good at hanging around. A cat with diarrhea gets cysts on its back end and back legs, grooms, and swallows them again. In cats, it takes about 5 to 16 days from swallowing cysts until new cysts appear in the stool, and shedding is often on and off.

Signs of Giardia in cats

Many infected cats show no signs. When they do get sick, the main sign is diarrhea, which can be sudden or drag on for weeks. Typical stool with Giardia is:

• Soft or poorly formed (sometimes liquid)
• Pale and unusually smelly
• Greasy-looking (fatty) or coated in mucus
• Occasionally streaked with blood

Other signs can include gas, belly discomfort, weight loss, and kittens that fail to gain weight. The CDC lists vomiting among the signs in pets, but CAPC notes that most infected cats do not vomit and do not run a fever. Ongoing diarrhea can also lead to dehydration in cats.

Who gets sick most often:

• Kittens and young cats (most clinical cases are in cats under a year old)
• Cats from shelters, catteries and other multicat homes
• Cats with a weakened immune system, such as cats with feline leukemia virus (FeLV) or FIV

How vets test for Giardia

Giardia is easy to miss. Cysts are tiny and see-through, and cats shed them on and off, so one clean sample does not rule it out. For cats with diarrhea, CAPC recommends a combination of tests on fresh stool:

1. Direct smear: a drop of fresh stool under the microscope to look for moving trophozoites.
2. Fecal flotation with centrifugation: a spin test (zinc sulfate is the preferred solution) that floats cysts up so they can be seen.
3. Fecal antigen test: an in-clinic or lab test that detects Giardia protein in the stool. PCR at a reference lab is another option, and some PCR tests can tell which type of Giardia it is.

Your vet may ask for samples from several days, because repeat testing over alternating days is sometimes the only way to catch it. Giardia tests made for people are not designed for pets, so don't use one on your cat.

What about a positive test in a cat that seems fine? CAPC says cats with signs should be treated. Cats without signs may not need treatment, depending on the type of Giardia and who else lives in the home: if the household includes someone who is immunocompromised, or vulnerable pets, CAPC advises treating. CAPC also says repeated courses of treatment are not indicated in cats without signs. Your vet makes the call with you.

How Giardia is treated

There is no drug approved for treating Giardia in cats in the US, so vets use medicines extra-label. The two options CAPC names for cats are fenbendazole (a dewormer) and metronidazole (an antibiotic that also acts on protozoa). Your vet chooses the medicine, the dose and how long to give it, based on your cat's age, health and any other medicines. A few things worth knowing:

• Metronidazole doesn't always work. CAPC reports cure rates as low as 50% to 60% for metronidazole in cats, and notes safety concerns with it.
• Other cats in the home may be treated at the same time, at your vet's discretion.
• Supportive care such as fluids for dehydration or an easily digestible diet may be added for cats that are quite sick.
• Never give leftover or human medicine. Not every antiparasitic is safe for cats: CAPC lists albendazole as unsafe in cats.

Live with a dog too? Dogs have their own Giardia types and treatment rules; our post on metronidazole for dogs covers the canine side.

The follow-up test matters. CAPC recommends a fecal flotation 24 to 48 hours after the treatment course ends. The timing is tight on purpose: cats can start shedding again within days of being reinfected, and a test done later can't tell reinfection from a treatment that didn't work. Antigen and PCR tests can stay positive for a while after treatment, so they are not used to judge whether the cat is cured.

Diarrhea can outlast the parasite. The gut lining needs time to heal, so loose stool may continue for a while after Giardia is gone. Tell your vet if it does, and see our guide to chronic diarrhea in cats for other causes worth ruling out.

Cleaning to stop reinfection

According to Today's Veterinary Practice, what looks like treatment failure is often reinfection. Medicine clears the gut, but cysts in the litter box, on the bedding and in the fur can start the whole thing again. The CDC suggests cleaning daily while your cat is on medication, until a few days after treatment ends:

1. Scoop the litter box at least once a day. Merck says to remove stool as soon as possible, and the CDC advises changing cat litter boxes every day.
2. Ask your vet about a bath. Merck and the CDC both recommend bathing infected cats to remove cysts and stool from the fur, and your vet may suggest a bath at the end of treatment. If your cat won't tolerate one, ask your vet how best to clean the fur.
3. Wash bedding, blankets, bowls and toys, then let them dry completely. Boiling water kills cysts.
4. Clean hard surfaces and the litter box itself with steam or a disinfectant (Merck lists most quaternary ammonium products), then let everything dry thoroughly. Cysts don't survive drying well.
5. Keep a new or sick cat separate from other cats until your vet clears it.
6. Wash your hands after scooping, cleaning or handling your cat.

If your cat goes outdoors, note that disinfectants won't kill Giardia in soil or grass, according to the CDC, which is one more reason the indoor routine matters.

Can people catch Giardia from cats?

It is possible but unlikely. The CDC puts it plainly: "you are unlikely to get a Giardia infection from your dog or cat."

The reason is that Giardia comes in genetic types called assemblages, and most stay with their own host species:

• Cats are mainly infected with assemblages F (a cat type) and AI.
• People are mainly infected with assemblages AII and B.
• Dogs mainly carry C and D, though dog types have occasionally been found in cats.

CAPC says cat-to-person spread appears to be rare except with assemblage AI, and human infections with the cat and dog types have not been conclusively shown in the US. Most people catch Giardia from other people or from contaminated water and food.

The risk goes up if someone in the home has a weakened immune system. That person should talk to their own doctor and consider limiting contact with the infected cat, and everyone should wash their hands after handling the litter box. If people and the cat are both infected, it does not automatically mean one gave it to the other.

When to call your vet

CAPC recommends parasite testing for cats every 6 months, and whenever a cat has signs such as diarrhea.

Common questions

Does Giardia go away on its own in cats? Some infected cats never show signs, and CAPC says cats without signs may not need treatment. A cat with diarrhea is different: it needs a vet exam and testing, because Giardia is only one of many causes of diarrhea and the cat can keep reinfecting itself.

Can I treat Giardia with coconut oil or other home remedies? No. Neither CAPC nor the Merck Veterinary Manual lists coconut oil or any other home remedy as a Giardia treatment. Treatment is prescription medicine from your vet plus cleaning.

Is there a Giardia vaccine for cats? Not anymore. A vaccine (GiardiaVax) was once used in the US, but it is no longer available.

How long until my cat is clear? That depends on the medicine your vet picks and how well reinfection is controlled. The follow-up stool flotation 24 to 48 hours after treatment is how your vet checks.

Originally written by Diana Wells. Updated by the I Love Veterinary editorial team.

Sources

• Companion Animal Parasite Council (CAPC): Giardia guidelines (cat), updated 2026
• Merck Veterinary Manual: Giardiasis in Animals
• CDC: About Giardia and Pets
• CDC: Giardia Infection: Causes and How It Spreads
• Gruffydd-Jones T, et al. Giardiasis in cats: ABCD guidelines on prevention and management. J Feline Med Surg 2013
• Saleh MN. Feline Giardia: Transmission, Diagnosis, and Treatment. Today's Veterinary Practice, 2021

This article is for general information and is not a substitute for advice from your veterinarian.