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Giardia: The Waterborne Gatecrasher
The smelly, stubborn diarrhoea with a microscopic cause.
Last reviewed
The smelly, stubborn diarrhoea with a microscopic cause.
Last reviewed
Giardia is not a worm but a single celled parasite that colonises the small intestine and interferes with digestion itself. Cats catch it by swallowing microscopic cysts from contaminated water, shared bowls, litter trays or grooming a contaminated coat, and the cysts are tough, surviving for weeks in damp environments.
It thrives wherever cats are young, stressed or gathered, which puts kittens, rescues and multi cat households squarely in its territory, and it is a name every responsible breeder knows and screens against.
The signature is soft, pale, greasy and notably foul smelling stools, on and off rather than constant, in a cat that often seems otherwise bright. Add weight loss or failure to thrive in kittens, occasional vomiting, and a coat losing its shine.
The pattern is the clue: an upset that keeps returning every time it seems to settle. Diagnosis needs the vet, usually a stool test, and sometimes more than one, because giardia sheds cysts intermittently and a single clear sample proves little.
Vets treat giardia with specific prescription medication over several days, sometimes adding a follow up course, and often a bath near the end of treatment to wash lingering cysts off the coat before the cat regrooms them.
The hygiene half is not optional: scoop trays immediately during treatment, disinfect trays and bowls with boiling water or a vet recommended disinfectant, wash bedding hot, and dry everything thoroughly, because dryness is what cysts cannot survive. Skip the hygiene and the medication chases its own tail.
Giardia alternates between two forms: the tough cyst that survives outside and the delicate swimming form that colonises the small intestine. Crucially, cysts are infectious the moment they leave the body, no ripening period, so a shared tray can pass giardia the same afternoon, and water bowls, damp floors and groomed coats all serve as couriers.
Cysts love damp and despise dryness, surviving weeks in wet corners and dying quickly on dry surfaces in sunlight. That single preference explains the whole hygiene protocol: boiling water, thorough drying, and the war on permanently damp bedding.
Giardia sheds cysts in bursts with quiet days between, so a single negative stool test is a snapshot of a quiet day, not an all clear. Vets work around it by pooling samples collected across three days, or by antigen tests that detect giardia proteins rather than hunting the cysts themselves.
The practical takeaway for owners: when the vet asks for a three day collection, the tedium is the test working properly, and when a relapsing tummy keeps testing clear, asking whether giardia has been specifically excluded is a fair and useful question.
The classic giardia failure is the final furlong: medication finishes, everyone relaxes, and the cat regrooms cysts off its own coat or laps them off a bowl washed cold. The organism gets a second season out of pure logistics.
Closing the loop looks like: the end of course bath the vet suggests, actually given; bowls through boiling water daily; trays scooped immediately and dried after washing; and in multi cat homes, the recheck sample before the patient rejoins shared trays. It is unglamorous, and it is the difference between treated once and treated monthly.
Giardia’s calling card is distinctive once known: soft rather than watery stools, pale, greasy or mucus coated, often strikingly foul smelling, arriving in episodes that improve and relapse over weeks. Weight slips gradually in youngsters while appetite often stays deceptively normal.
That intermittent pattern is why owners so often report a tummy bug that keeps coming back: each apparent recovery is the parasite’s quiet phase, not its departure. A tray diary, dates and descriptions, turns vague recollection into the pattern a vet can act on.
Giardia’s cysts travel by water: puddles, ponds, shared outdoor bowls and any damp ground contaminated by an infected animal’s droppings. A cat drinking from the garden saucer or grooming wet paws after a catio downpour can swallow an infection invisibly.
Household prevention is therefore mostly plumbing: fresh indoor water stations cats actually like, outdoor bowls emptied rather than topped up, standing water discouraged in the catio, and pond access designed out. The parasite cannot be seen, but its taxi service can be cancelled.
A Ragdoll’s glorious trousers are giardia’s favourite loophole: cysts from a soft stool cling to rear end fur, and the cat’s meticulous grooming delivers them straight back to the mouth. Treatment can be perfect and still lose to the coat.
During any giardia course, long haired cats get rear hygiene as part of the medicine: soiled fur cleaned promptly, a sanitary trim if your vet or groomer advises, and a final clean up bath or wipe down at treatment’s end on veterinary guidance. It feels undignified; it is frequently the difference between cure and relapse.
In multi cat homes giardia behaves like a shared subscription: the symptomatic cat is often just the one whose gut complains loudest, while housemates shed cysts in comfortable silence. Treating one cat into a contaminated group buys a fortnight of peace and then a relapse.
Your vet may advise testing or treating contacts together, and the environmental campaign, trays scrubbed with boiling water and dried fully, litter changed completely, bedding hot washed, runs across the whole household once. One synchronized effort beats three sequential ones by months.
Giardia is a microscopic gut parasite spread through contaminated water, ground and grooming, causing soft, greasy, foul smelling stools that come and go. It is confirmed with laboratory tests, treated with a prescription course, and beaten at home by pairing the medicine with hygiene: trays scrubbed, rear ends of long haired cats kept clean, and reinfection loops closed.
Human giardia cases mostly involve different strains and waterborne sources, and transmission from cats appears uncommon, but the hygiene rules apply regardless: gloves or washed hands for tray duty, especially for the immunocompromised.
Giardia sheds intermittently, so single samples miss it; vets often pool samples across three days or use antigen tests to catch it. A negative on one casual sample does not close the case.
A typical prescription course runs days to a couple of weeks, often paired with the hygiene campaign and sometimes repeated. The recheck sample matters more than the calendar; finished is a lab result, not an empty packet.
Almost never: once cleared, young guts recover fully and thrive. The episode’s real legacy should be paperwork, records of treatment and the all clear, travelling home with the kitten.
No: it means water and ground did what water and ground do. Spotless households meet giardia through one puddle or one new arrival; response, not blame, is the useful reaction.
Some robust adults do self resolve, but youngsters, seniors and anything symptomatic beyond days deserve the course: untreated carriers keep seeding the environment. The cheap stool test beats the long gamble.
The nursing basics live in our poorly tummy guide, and giardia’s partner in crime has its own page: meet coccidia next.
To research giardia properly, ESCCAP publishes the intestinal protozoa guidelines, and Cornell Feline Health Center explains testing and treatment in clinical detail. See the culprit itself: the Giardia page includes the microscope imagery.