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Feline Calicivirus: The Mouth Ulcer Virus
Cat flu’s second author, with a signature all its own.
Last reviewed
Cat flu’s second author, with a signature all its own.
Last reviewed
Calicivirus is the other half of the cat flu partnership, and where herpesvirus loves eyes, calicivirus loves mouths. It is extremely common wherever cats gather, spreads on sneezes, surfaces and hands, and is notoriously hardy in the environment.
Most infections look like standard cat flu and pass with nursing. Its signatures are what make it worth knowing by name.
Signature one: mouth ulcers, on the tongue, gums or palate. The tell is a cat clearly hungry who approaches food then backs away, drools, or drops pieces, sometimes with a suddenly terrible breath. Lift the lip gently and raw patches may be visible.
Signature two, mostly in kittens: limping kitten syndrome, a short lived fever with shifting lameness, sore joints today gone in a few days. Alarming to watch, usually self resolving, but always worth a vet confirming that is what it is.
Nursing is cat flu care with a mouth focused menu: soft, strong smelling food, slightly warmed, soup textures if chewing hurts, and pain relief from the vet when ulcers are bad, because a cat that stops eating stops recovering.
The cleanup matters more than most viruses: calicivirus laughs at many ordinary disinfectants and survives on surfaces for weeks. A suitable veterinary disinfectant used as directed on bowls, bedding and surfaces is the way this leaves a multi cat household rather than circulating.
Calicivirus mutates readily, existing as a cloud of strains rather than a single fixed enemy. That diversity is why vaccinated cats can still catch a version the vaccine only partly matches, why immunity after recovery is not always immunity to the next strain, and why the virus never quite leaves the feline population.
None of this makes vaccination pointless: the core strains in the jab cover the common ground and reliably blunt severity. It simply resets expectations: with calicivirus the goal is mild and brief, not never.
Very occasionally a calicivirus strain turns virulent and systemic, causing severe illness with fever, swelling and jaundice, almost always inside dense group settings such as shelters, and making veterinary news precisely because it is rare. It is worth knowing it exists; it is not worth fearing behind every household sneeze.
The proportionate takeaway for owners is simply this: an ordinary snuffly cat is ordinary, but a cat with flu signs plus swelling of the face or paws, jaundice or collapse is an emergency by any reading, and group facilities with multiple sudden severe cases need veterinary authorities involved fast.
Calicivirus survives on dry surfaces for as much as a month and shrugs off many everyday disinfectants, which is why flu keeps lapping multi cat homes that clean diligently with the wrong bottle. The winning chemistry is a proper veterinary virucide or suitably diluted bleach on the hard surfaces, used exactly to label, with contact time respected.
The soft campaign runs alongside: bowls through boiling water daily during an outbreak, bedding hot washed, litter trays cleaned and fully dried, and the recovering patient’s kit kept separate until well after the sneezing ends, because the shedding outlasts the symptoms.
When the tongue is ulcerated, food design decides intake: smooth pates over chunks, everything warmed to release smell and soften texture, small amounts offered often, and gravity helped with a slightly raised dish so a sore mouth does not have to work at floor level. Sharp kibble is off the menu until healing.
Water gets the same care, fresh, room temperature and everywhere, because ulcerated mouths under drink. What home care never becomes is force feeding; a cat defeating even warmed pate has crossed into the vet’s territory, where pain relief and support turn the strike around.
Calicivirus occasionally adds a twist that catches owners off guard: a transient limping syndrome, especially in kittens, where joints briefly inflame and a snuffly youngster hobbles or shifts lameness leg to leg. It looks alarming and typically passes within days with veterinary support.
Knowing the link matters twice: it stops a limping, sneezy kitten being read as an injury case alone, and it adds one more reason young cats with flu signs get seen rather than watched. Mention the sneezes and the limp together; the combination is the clue.
In a litter, calicivirus finds its ideal conditions: close contact around shared bowls and beds, immune systems mid construction, and mouths already busy with teething. One sneezing kitten reliably becomes four, and small patients with sore mouths skip meals they cannot afford to skip.
That multiplier is why breeders and fosterers treat a first calici sneeze as a same day matter and why weights get logged daily through any litter outbreak. For buyers, a nursery’s answer to how sneezes are handled tells you how this exact scenario would have gone.
For most cats calici is an episode; for a minority it leaves a tenant, with the virus implicated in chronic inflammation of gums and mouth that persists long after the flu, part of the severe condition our dental guide describes. Suspect it in a recovered cat whose gums stay angry red or whose breath and appetite never fully return.
That is a vet conversation, not a wait and see: chronic mouth inflammation is painful, manageable and worth naming early. Say the calici history when you book, because it genuinely reshapes the differential.
Calicivirus is the mouth ulcer member of the cat flu family: sneezes plus a painfully ulcerated tongue that puts cats off food. Care is veterinary pain relief and soft, warmed, strong smelling meals while immunity wins, with hygiene run hard because this virus travels on surfaces and shrugs at many cleaners. A drooling cat that will not eat sees the vet today.
Broadly, calici leads with mouth ulcers and drooling while herpes leads with eyes and lifelong flares; sneezing is common to both and mixed infections happen. Vets sometimes swab exactly because the emphasis changes the plan.
Shedding typically continues for weeks after recovery, and in a minority of cats for months. That long tail is why new kitten introductions after a calici episode deserve a word with your vet.
No: feline calicivirus is species adapted, and the household’s humans and dogs are bystanders. The hygiene campaign protects the other cats, not the people.
No: vaccination is likely why the case is staying mild, with fewer ulcers and a faster recovery. Against a shape shifting virus, protection is a dimmer switch rather than an off switch, and dimmer is valuable.
When eating stops for a day, when lethargy or dehydration sets in, in any very young kitten, or with laboured breathing. Mouth pain defeating even warmed soft food is a same day call, because nutrition is the recovery.
Yes: a mouth or eye swab sent for laboratory analysis can name the virus, useful in litters, catteries and stubborn cases where the culprit changes the plan. For a single mild household case, many vets treat on the clinical picture.
The general nursing rules live in the cat flu guide, and mouth health has a whole chapter of its own in dental care.
Beyond our library, International Cat Care covers this in owner friendly depth, and Cornell Feline Health Center adds the clinical detail. And to see the culprit itself, the photographs on the feline calicivirus page show exactly what science is dealing with.