Giardia in Cats: The Parasite Behind Diarrhea That Isn't a Worm
A round of dewormer that doesn't fix your cat's soft, mucousy poop is usually what gets a vet testing for giardia. It's a genuinely common cause of cat diarrhea, and it's not a worm at all, so the stuff that clears roundworms or tapeworms won't touch it.
What giardia actually is
Giardia's a single-celled parasite that sets up shop in the small intestine. It spreads through cysts in poop that contaminate food, water, or a shared space like a litter box or shelter floor. It's one of the more common gut parasites in cats, especially young cats and ones in crowded shelters or multi-cat homes.
What symptoms actually look like
In adult cats giardia is often subclinical, meaning the cat's carrying and shedding it with no obvious illness, or just some mild, temporary soft stool. Kittens usually have it worse, more noticeable diarrhea that's pale, greasy-looking and unusually foul, sometimes with visible mucus.
The zoonotic risk question, and why it's more nuanced than it sounds
Giardia gets lumped into "can I catch this from my cat" worries, but the real picture's more specific. Giardia comes in genetically distinct types, and cats mostly carry assemblage F, a cat-specific strain that isn't known to infect people. Cats can, less often, carry assemblages A or B, the ones tied to human infection, so a real zoonotic-risk case is possible, it's just the exception, not the rule.
How it's actually diagnosed
Giardia cysts don't shed consistently, so one fecal sample alone is an unreliable test. The most reliable approach combines a fecal flotation spun in a centrifuge with a specific ELISA antigen test, since a plain smear alone misses real infections. A PCR test can identify which assemblage is present too, which is the only way to actually know if a given case carries real zoonotic risk.
Treatment
Fenbendazole or metronidazole are the go-to treatments. A bath to rinse cysts out of the fur around the back end often gets recommended alongside meds, since a cat can reinfect itself just by grooming. Treatment's clearly worth it for any cat showing symptoms, and for symptom-free cats carrying a zoonotic-risk assemblage. Symptom-free cats with the cat-only assemblage F don't necessarily need treatment at all.
What treatment costs
A basic case, meds plus a fecal test to confirm it, usually runs somewhere in the $100 to $250 range. Shelters and multi-cat homes dealing with an outbreak spend more, since testing and treating every cat in the group adds up fast.
Recovery timeline
Most cats clear symptoms within a week or two of starting treatment, though it can take a second round of meds if the first didn't fully knock it out. Cysts can linger in the environment longer than the illness does, which is why cleaning matters just as much as the medication.
Preventing spread in multi-cat households
According to the Petfinnly's research, giardia cysts can survive for weeks in a damp environment, so thorough litter box cleaning, prompt poop pickup and washing bedding during an active infection all cut down reinfection risk. In shelters, where crowding makes giardia stick around, isolating diarrheic cats fast is standard practice for exactly this reason.
Frequently asked questions
My dog has giardia, can he give it to my cat or the other way around?
It's uncommon. Dog and cat giardia strains are mostly species-specific, so it can jump between your dog and cat but it's not the typical way infections spread. Each species tends to stick to its own strain.
Why didn't dewormer clear up my cat's diarrhea?
Because giardia's not a worm, it's a protozoan parasite, so the regular over-the-counter dewormers made for roundworms and tapeworms just don't touch it. It needs something specific like fenbendazole or metronidazole, which is why an actual stool test matters instead of just guessing at the cause.
My cat finished her giardia treatment, why does she have diarrhea again a month later?
Probably reinfection, especially in a dirty environment or multi-cat home where cysts hang around in bedding or the litter box. Washing bedding, deep-cleaning the litter box and picking up poop right away alongside the meds is what actually makes it stick instead of just clearing symptoms for a while.
This article is for general information and isn't a substitute for advice from your own veterinarian, who can properly diagnose and treat diarrhea in your specific cat.
