My Cat Has Greasy, Foul-Smelling Stool. Could It Be Giardia?

If your cat has been leaving soft, greasy, foul-smelling stool in the litter box, giardia might be the culprit. It’s a common intestinal parasite, and the good news is that it’s treatable. The less-good news: it can be stubborn, especially in multi-cat households, because the tiny cysts it leaves behind are remarkably hard to kill.

Here’s what you need to know about giardia in cats.

What is giardia in cats?

Giardia is a microscopic, single-celled parasite (called a protozoan) that takes up residence in your cat’s small intestine and disrupts how food is absorbed. It’s not a worm or a bacteria. It’s its own category of trouble.

The parasite spreads through the fecal-oral route: a cat gets infected by ingesting cysts (the dormant, infectious form of the parasite) shed in another animal’s feces. This can happen through contaminated water, shared litter boxes, or even just grooming after walking through a contaminated area. Indoor cats aren’t immune, especially in multi-cat homes.

Signs of giardia in cats

The most telling sign is the stool itself. Giardia in cats poop tends to look different from a typical upset stomach: it’s often pale, soft, greasy, and carries a particularly foul smell. You might also notice it has a mucus-like coating.

Other signs to watch for include:

• Chronic or intermittent diarrhea (sometimes soft stool, sometimes more watery)
• Weight loss or failure to gain weight, even with a normal appetite
• Lethargy or generally seeming off
• Vomiting (less common, but it happens)
• A coat that looks dull or unkempt

Some cats carry giardia without any obvious symptoms at all. That’s part of what makes it tricky, especially in shared spaces where a seemingly healthy cat can infect others.

Diagnosis and treatment

Your vet will diagnose giardia through a fecal test. This usually involves a fecal float (where stool is mixed with a solution that makes cysts rise to the surface for microscopic examination) or an antigen test, which detects proteins released by the parasite. Because cysts aren’t shed constantly, vets sometimes ask for samples from multiple days to catch it.

Treatment for giardia in cats typically involves one or both of these medications:

• Fenbendazole (Panacur): an antiparasitic medication given over several days, often 5 days or more. It works by disrupting the parasite’s ability to absorb nutrients.
• Metronidazole: an antibiotic and antiparasitic that targets the parasite directly. It’s sometimes used alongside fenbendazole for more stubborn cases.

Your vet will determine the right protocol for your cat. Never try to treat giardia at home with over-the-counter products without veterinary guidance; dosing matters, and some treatments safe for dogs aren’t safe for cats.

Why giardia keeps coming back: breaking the reinfection loop

This is the part most articles gloss over, and it’s the reason so many cats end up right back at the vet a few weeks after finishing treatment. Medication kills the active parasite inside your cat’s gut. It does not eliminate the cysts already living in your home.

Giardia cysts are remarkably hardy. They can survive for weeks in a damp environment, and they can cling to your cat’s fur, particularly around the hindquarters, after using the litter box. If your cat grooms itself (which cats do, constantly), it can reinfect itself before the medication even has a chance to fully clear things up.

Breaking the reinfection loop means treating the environment and your cat’s coat, not just the gut. Here’s what that looks like in practice:

• Bathe your cat during and after treatment to remove cysts from the coat. Focus on the rear end. Yes, cats hate baths. Do it anyway.
• Clean the litter box daily throughout treatment, and disinfect it with a diluted bleach solution (1:32 bleach to water) regularly. Let it dry fully before reuse.
• Wash bedding and soft surfaces your cat uses frequently. Giardia cysts are killed by heat, so a hot wash cycle helps.
• Reduce moisture in the environment where possible. Cysts survive longer in damp conditions.
• In multi-cat homes, treat all cats even if only one is showing symptoms. Asymptomatic cats can be shedding cysts and reinfecting the others.

The medication does its job. Environmental decontamination and bathing are what keep the job done.

Is giardia contagious? What about humans?

Giardia is contagious between cats, and it is technically zoonotic, meaning it can spread from animals to humans. That said, the strains that commonly infect cats are generally not the same strains that cause illness in people, so the risk of catching giardia from your cat is considered low.

That doesn’t mean you should skip precautions. During treatment, wash your hands thoroughly after handling your cat or cleaning the litter box, and keep children away from the litter area. If anyone in your household is immunocompromised, talk to your doctor for guidance specific to your situation.

Does giardia in cats go away on its own? Sometimes, in otherwise healthy adult cats, mild cases resolve without treatment. But that’s not a reliable outcome, and an untreated cat can continue shedding cysts and spreading infection to other animals (and theoretically, humans) in the home. If you see the signs, call your vet.

Does pet insurance cover giardia in cats?

Treating giardia isn’t outrageously expensive, but the costs add up: fecal testing, medication, a follow-up visit to confirm clearance, and potentially a second round of treatment if reinfection occurs.

Giardia is covered under Lemonade Pet illness coverage, as long as it’s not pre-existing and develops after the applicable illness waiting period has passed. If your cat already has giardia when you enroll, that illness won’t be eligible for reimbursement. Enrolling before any symptoms appear is what keeps future illnesses within reach of coverage.

Before we go

Giardia is stressful, but it’s manageable. The combination of the right medication from your vet, thorough cleaning at home, and a few targeted baths breaks the cycle for most cats. If your cat’s stool looks off, greasy, or consistently soft, don’t wait it out. A quick fecal test can confirm what’s going on and get treatment started. And if you haven’t looked into pet insurance yet, now’s a good time. Getting coverage in place before your cat gets sick is the only way to make sure it’s there when you need it.

Frequently Asked Questions

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