Feline Calicivirus in Cats: Signs, Care, and Prevention

Feline calicivirus is one of the two viruses most commonly behind what owners call cat flu, alongside feline herpesvirus. It is extremely widespread in cat populations worldwide, spreads readily wherever cats live in groups, and is particularly familiar to anyone who has fostered, worked in rescue, or brought home a kitten from a busy environment.

What makes calicivirus distinctive is that it is not purely a respiratory virus. Its signature feature in many cats is painful ulceration in the mouth — on the tongue, the hard palate, or the edges of the lips — which explains why an affected cat may drool, paw at the mouth, or stop eating entirely while their nose seems relatively clear. That combination catches owners off guard.

This guide covers how calicivirus behaves, what the signs look like, how it spreads and persists, what supportive care typically involves, and where vaccination fits into prevention. If your cat is currently unwell, particularly if they have stopped eating or are having any difficulty breathing, contact your veterinary practice rather than reading on.

Important: This article shares general educational information for pet owners and is not a substitute for an in-person veterinary examination, diagnosis, or treatment. For any medical concern or emergency, contact your veterinarian promptly.

What Feline Calicivirus Is

Feline calicivirus, usually abbreviated to FCV, is a virus that infects cats and typically targets the upper respiratory tract and the tissues of the mouth. It is a cat-specific virus: it does not infect people, and it is not the same thing as the caliciviruses that cause illness in humans.

One of its defining characteristics is variability. Calicivirus exists as many different strains, and they do not all behave the same way. Some produce mild, self-limiting illness that resolves in a week or two. Others cause more significant oral disease. A small number of unusual strains have been associated with far more severe systemic illness, though these are uncommon.

That strain diversity has practical consequences. It is why two cats in the same household can have noticeably different illnesses from the same outbreak, and it is part of why vaccination reduces the severity of disease rather than guaranteeing a cat will never become infected at all.

How It Spreads Between Cats

Transmission happens mainly through direct contact with an infected cat's secretions — saliva, nasal discharge and eye discharge. Cats grooming each other, sharing bowls, sneezing at close quarters or simply living in the same room pass it along efficiently.

Indirect transmission matters too. The virus can persist in the environment on surfaces, bedding, bowls and litter trays for a period, and it can travel on human hands, clothing and shoes. This is why someone who has handled an infected cat elsewhere can bring the virus home to an indoor-only cat who has never met another animal.

Calicivirus is also relatively resistant to many ordinary household cleaners compared with some other viruses, which matters for outbreak control. Your veterinarian can advise on appropriate disinfection for a household or fostering situation — it is worth asking specifically rather than assuming a standard spray will do the job.

The Signs Owners Notice First

Illness typically develops within a few days of exposure. The presentation varies with the strain, the cat's age, and their immune and vaccination status, but certain patterns recur.

Common signs

• Mouth ulcers — the hallmark of calicivirus, often on the tongue, palate or lip margins, and genuinely painful.
• Drooling — frequently the first thing owners notice, sometimes with the cat holding the mouth slightly open.
• Sudden loss of appetite — cats with oral ulceration may approach food, show interest, then back away because eating hurts.
• Sneezing and nasal discharge — usually present, though sometimes milder than the oral signs.
• Eye discharge and conjunctivitis — redness, squinting and watering.
• Fever and lethargy — a cat who is hiding, quiet and unusually still.
• Lameness — some cats, especially kittens, develop a transient shifting lameness that can precede or accompany other signs.

The lameness presentation confuses owners reasonably often, because a limping kitten does not obviously suggest a respiratory virus. If a kitten develops a shifting lameness alongside a fever or any respiratory or oral signs, mention the combination to your veterinarian.

Calicivirus Versus Herpesvirus

Both viruses cause cat flu and both are common, so owners frequently ask which one their cat has. The honest answer is that the two overlap considerably and cannot be distinguished by appearance alone, though there are tendencies.

Calicivirus is more strongly associated with oral ulceration, drooling and sometimes lameness. Feline herpesvirus is more strongly associated with marked eye involvement, including corneal disease, and with severe sneezing. Herpesvirus also has a well-recognised tendency to become latent and reactivate during periods of stress, producing recurring flare-ups throughout life.

Confirming which virus is involved requires laboratory testing, and in many straightforward cases veterinarians treat supportively without testing, because the supportive care is broadly similar. Testing becomes more relevant in severe cases, recurrent problems, or in multi-cat households, shelters and breeding situations where knowing matters for management.

Why Some Cats Stay Infectious Afterwards

This is the part that surprises most owners. A meaningful proportion of cats who recover from calicivirus continue shedding the virus afterwards, sometimes for a prolonged period, while appearing entirely healthy. These carrier cats are a major reason the virus stays so widespread in cat populations.

A carrier cat looks and behaves normally. They are not unwell, they do not need treatment for being a carrier, and owners should not feel they have done anything wrong. The practical implication is simply that introducing a new cat into a household, or taking a cat into a group setting, carries some risk of transmission that cannot be eliminated by observation alone.

If you foster, breed, or run a multi-cat household, discuss a sensible management approach with your veterinarian. That conversation is far more useful than trying to identify carriers informally, since there is nothing to see.

How It Is Diagnosed

Most cases are diagnosed clinically: a cat with typical signs, an appropriate history, and a physical examination that finds oral ulceration, nasal and ocular discharge and fever. Your veterinarian will examine the mouth carefully, which often requires care because the ulcers are sore.

Where confirmation is needed, swabs from the mouth, throat or eyes can be submitted for laboratory testing. Additional tests may be recommended depending on the cat — blood work in a cat who is systemically unwell, imaging if the chest is involved, or testing for other infections that can complicate the picture.

Tell your veterinarian about the full history: vaccination status, where the cat came from, whether other cats in the home are affected, whether any new cat has arrived recently, and whether anyone has been handling other cats elsewhere. That context often shapes the assessment more than any single test result.

Supportive Care: What Actually Helps

There is no antiviral cure that simply eliminates calicivirus. Treatment is supportive, aimed at keeping the cat comfortable, hydrated and eating while their own immune system deals with the infection. That said, supportive care is not passive — it is often what determines how well a cat comes through.

Pain relief matters enormously here and should always be prescribed by a veterinarian. Oral ulcers are painful, and a cat in pain will not eat. Never give human painkillers to a cat under any circumstances; several common human medications are severely toxic to cats even in small amounts.

Your veterinarian may also prescribe medication for nausea, fluid therapy for a dehydrated cat, treatment for secondary bacterial infection where it has developed, and eye treatment where the eyes are involved. Hospitalisation is sometimes needed for cats who are not eating or drinking adequately, and that is a reasonable and often the right decision rather than a failure of home care.

Nursing a Cat With Cat Flu at Home

Home nursing focuses on comfort, nutrition and hygiene, alongside whatever your veterinarian has prescribed.

• Encourage eating — warming food gently increases aroma; soft or wet food is far easier on an ulcerated mouth than dry kibble.
• Keep the face clean — gently wipe discharge from the eyes and nose with damp cotton wool, using a fresh piece for each eye.
• Support the airway — sitting with your cat in a steamy bathroom can help loosen nasal congestion, but never use decongestants or inhalants intended for people.
• Provide warmth and quiet — a warm, draught-free, low-traffic resting place helps considerably.
• Keep water close — place bowls near resting spots so a weak cat does not have to travel.
• Monitor intake — note what actually goes in each day, since a cat who is not eating needs veterinary review quickly.

A cat that has not eaten for a day or two needs veterinary attention, not more encouragement at home. Cats are particularly vulnerable to complications when they stop eating, and this is one of the most important thresholds for owners to know.

Protecting Other Cats in the Home

Where practical, isolate the affected cat in a separate room with their own bowls, bedding and litter tray. Care for the healthy cats first and the unwell cat last, and wash your hands thoroughly between. Changing an outer layer of clothing after handling the sick cat is a small step that helps.

Wash bowls, bedding and toys thoroughly and frequently. Ask your veterinarian which disinfectant is appropriate and how to use it safely around cats, since calicivirus is less easily inactivated than some viruses and several disinfectants are themselves hazardous to cats.

Complete separation is often impossible in a normal home, and in a household where cats already share space, other cats may well have been exposed before any signs appeared. Do what is reasonably practical rather than aiming for perfection, and tell your veterinarian how many cats are involved so they can advise on monitoring the rest.

Vaccination and Prevention

Vaccination against feline calicivirus is part of the core vaccination protocol recommended for cats in most of the world, typically given in combination with protection against feline herpesvirus and panleukopenia. Kittens receive an initial course followed by boosters, with ongoing revaccination intervals determined by your veterinarian based on the vaccine used, your cat's lifestyle and local guidance.

It is important to set expectations correctly. Because of the number of circulating strains, vaccination is generally understood to reduce the severity of disease rather than to prevent infection entirely. A vaccinated cat may still become infected, but typically has a milder illness. That is a meaningful benefit, not a shortcoming, and it is exactly why vaccination remains recommended.

Alongside vaccination, prevention rests on sensible practices: quarantining new arrivals before introducing them, hand hygiene after contact with cats outside the household, not sharing equipment between groups of cats, and keeping up with routine veterinary checks. Supplements and general wellness products are a complement to this rather than a substitute, and nothing replaces vaccination or veterinary care.

When to Seek Urgent Veterinary Help

Most cases of cat flu are uncomfortable rather than life-threatening, but several situations need prompt attention.

Call your veterinary practice before arriving with a cat suspected of having cat flu, so they can advise on how to bring your cat in without exposing other patients in the waiting room. Practices deal with this frequently and will have a straightforward plan.