Calicivirus in Cats: Signs, Treatment and Prevention

For information only. This article supports, and never replaces, an examination by a veterinarian.

Feline calicivirus (FCV) is one of the most common causes of "cat flu", the sneezy, runny-eyed upper respiratory infection that sweeps through shelters and multi-cat homes. Its calling card is painful ulcers on the tongue, so a cat with calicivirus often drools and stops eating even when the sneezing is mild.

Most cats recover in days to a few weeks with supportive care from their vet. A small number get pneumonia, and a rare virulent strain can be deadly, so it pays to know which signs mean call the vet right now.

Call your vet now if you see these signs

Fast, labored or open-mouth breathing while your cat is resting (Cornell's Feline Health Center says a resting cat should not take more than 35 breaths a minute)
A kitten with calicivirus signs that is weak, coughing or not eating
Swelling of the face, head or legs, or crusting sores on the nose, lips, ears, around the eyes or on the paw pads
Yellow gums, skin or eyes (jaundice), bruising, a nosebleed or blood in the stool
Several cats in the same home or shelter falling seriously ill at once

Call your vet today if your cat has mouth ulcers or drooling, has stopped eating or drinking, has a fever or seems very flat, or is suddenly limping. See your vet soon if your cat is only sneezing mildly and still eating. A sneezy cat still deserves a vet check, and your vet can tell you how to protect your other cats.

Signs of calicivirus in cats

Signs usually start 2 to 10 days after exposure, according to the European Advisory Board on Cat Diseases (ABCD). Other sources give slightly different windows: the Merck Veterinary Manual says 2 to 6 days. Kittens are hit hardest. What a cat shows depends a lot on the strain, and some infected cats show nothing at all.

Diagram of a cat showing where calicivirus causes signs: mouth ulcers, sneezing, eye discharge, breathing problems, kitten limping, and the emergency signs of virulent systemic calicivirus — Infographic by I Love Veterinary

Mouth ulcers and drooling

Blisters form on the tongue and break open into ulcers. These are the most typical calicivirus lesion, and they can also appear on the roof of the mouth, the lips or the nose. The ulcers hurt, so cats drool, paw at the mouth or walk up to the food bowl and walk away again. ABCD notes that not eating is often more noticeable than the sneezing.

Cold-like signs (upper respiratory infection)

Sneezing
Clear nasal discharge that may turn thick if bacteria move in
Watery eyes and red, swollen inner eyelids (conjunctivitis)
Fever, tiredness and poor appetite

Merck describes milder cases lasting 5 to 10 days and severe cases up to 6 weeks. In some cats, especially young kittens, the virus moves down into the lungs and causes pneumonia. Watch for coughing, fast breathing or a cat that breathes with effort.

Kitten with crusted, half-closed eyes and discharge around the nose, typical of cat flu — Crusted, half-closed eyes and a messy nose are classic cat flu signs. Calicivirus and herpesvirus can both look like this.

Limping syndrome in kittens

Some strains cause a sudden, painful lameness with fever, often in kittens around 8 to 12 weeks old. The limp can jump from one leg to another, sometimes with no mouth or nose signs at all. ABCD notes that full recovery usually happens within a day or two. In rare cases the same temporary limp follows a calicivirus vaccine, Cornell and ABCD note. A limping kitten still needs a vet check to rule out other causes, such as an injury.

Chronic gum and mouth inflammation (FCGS)

Feline chronic gingivostomatitis (FCGS) is a painful, long-term inflammation of the gums and the tissue at the back of the mouth. Calicivirus is found more often in cats with FCGS than in healthy cats: in one study 54% of cats with FCGS tested positive against 24% of healthy cats. The virus seems to play a part, but it is not the whole story, and the condition is thought to involve the cat's own immune response. Our guide to stomatitis in cats covers it in more detail.

Virulent systemic calicivirus: an emergency

Very rarely, a mutated strain called virulent systemic feline calicivirus (VS-FCV) appears. It attacks blood vessels and organs throughout the body. Outbreaks usually start in shelters, catteries or vet clinics and spread fast, and unlike ordinary calicivirus, they tend to hit adult cats harder than kittens. Signs include:

High fever
Swelling of the head and legs
Crusting sores, ulcers and hair loss on the nose, lips, ears, around the eyes and on the paw pads
Yellow gums or skin (jaundice)
Bleeding: tiny red spots, bruises, nosebleeds or bloody stool
Trouble breathing

ABCD puts the death rate in outbreaks at roughly 30 to 70%. Vaccinated cats are not reliably protected. If you see these signs, call your vet before you go in, so the clinic can keep your cat away from other cats.

Calicivirus or herpesvirus?

Feline herpesvirus 1 (FHV-1) causes the other big share of cat flu, and the two often show up together. Merck notes that it is often impossible to tell them apart from the signs alone, but each has its tendencies:

	Feline calicivirus (FCV)	Feline herpesvirus 1 (FHV-1)
Typical clue	Ulcers on the tongue and in the mouth, drooling	Eye and nose signs; ulcers on the surface of the eye (cornea)
Other signs	Pneumonia, limping syndrome in kittens	Nasal and eye discharge, conjunctivitis
After recovery	Many cats shed for at least 30 days, a few for years	Up to 80% of exposed cats stay infected for life
Shedding	Continuous while the cat is a carrier	On and off, often after stress
Vaccine	Core vaccine, combined with FHV-1	Core vaccine, combined with FCV

Calicivirus vs herpesvirus in cats: calicivirus causes mouth ulcers and limping, herpesvirus causes eye and nose signs; they often look alike and both are covered by the core vaccine — Infographic by I Love Veterinary

Your vet can confirm which virus (or both) with a swab test. For the herpes side of the story, see our guide to feline herpes. Bacteria such as Bordetella bronchiseptica, Chlamydia felis and Mycoplasma can join in and make things worse, which is why vets talk about a complex of respiratory illnesses rather than one disease.

How calicivirus spreads

Calicivirus is highly contagious. Infected cats shed it mainly in saliva and nose and eye discharge, and it has also been found in blood, urine and feces. Cats catch it through:

Direct contact with an infected cat: grooming, sharing food, fighting
Contaminated objects (fomites): food and water bowls, litter boxes, bedding, cages, and people's hands and clothes
Sneezed droplets, and in crowded facilities, airborne spread, which ABCD reports has been detected where shedding cats are housed

The virus is tough. It can stay infectious on dry surfaces for up to a month at room temperature, and longer in the cold. More on routes like these in our article on how feline diseases are transmitted.

Carriers: cats that look healthy but still spread it

This is the part that surprises owners. After recovering, many cats keep shedding the virus for at least 30 days, and a few shed for years or for life, according to ABCD. Some cats never look sick at all. That is why calicivirus is so common where many cats live together: Cornell estimates that about 10% of cats in small groups are infected, compared with up to 90% in more crowded conditions such as shelters and breeding catteries.

How vets diagnose calicivirus

Often the picture is clear enough from the exam: mouth ulcers plus sneezing in a young or newly adopted cat. When the answer matters, for example in a multi-cat home, a shelter or a severe case, the vet swabs the mouth, throat and eyes for an RT-PCR test, which detects the virus's genetic material.

Test results need careful reading. A negative result does not rule calicivirus out, and healthy carriers, or cats recently given a modified-live vaccine, can test positive. Commercial tests also cannot tell an ordinary strain from a virulent systemic one; that judgment rests on the signs and how the illness spreads through a group.

Treatment: supportive care from your vet

There is no proven antiviral cure for calicivirus. Treatment supports the cat while its immune system clears the infection, and your veterinarian chooses every medicine and dose. Depending on how sick the cat is, that can include:

Pain relief and fever control. ABCD advises that anti-inflammatory pain relievers are given only after the vet has corrected any dehydration, so pain relief is always the vet's call.
Fluids for dehydration, given through an IV drip in severe cases.
Antibiotics when a secondary bacterial infection is suspected. They do not touch the virus.
Help with congestion, such as saline nebulization or a mucus-thinning medicine.
Help with eating: an appetite stimulant, or a feeding tube that lets food bypass the sore mouth until the ulcers heal.
Hospital care with oxygen and intensive nursing for pneumonia or virulent systemic disease.

Cornell's Feline Health Center notes that cats with uncomplicated respiratory disease, pneumonia or mouth ulcers may recover in days or weeks. Cats with virulent systemic disease have a much poorer outlook.

What you can do at home while your cat recovers

Home care is comfort care. It works alongside your vet's plan, never instead of it. ABCD and Cornell suggest:

Tempt the appetite. Offer soft, strong-smelling food, warmed slightly and blended or mashed if the mouth is sore. A blocked nose dulls smell, and smell drives a cat's appetite. Hand feeding helps some cats.
Keep the face clean. Gently wipe discharge from the eyes and nose with a soft cloth or cotton pad moistened with saline, or whatever your vet recommends.
Add steam. Sit with your cat in a closed bathroom while a hot shower runs. ABCD's rule of thumb: the humidity is right when the mirror fogs up.
Keep the sick cat apart from other cats, with its own bowls, litter box and bedding, and wash your hands after handling it.

Watch the food bowl. Call your vet the same day your cat stops eating or drinking. Cats get sick fast without food, so this is not a sign to wait out. For context, ABCD's guideline says a cat that has not eaten for more than three days needs a feeding tube. Kittens tend to get sicker than adult cats, so call sooner rather than later, and watch for signs of dehydration.

When to call the vet about calicivirus: call now for breathing trouble or virulent signs, call today for mouth ulcers or not eating, and see your vet soon for mild sneezing — Infographic by I Love Veterinary

Cleaning up: how to kill calicivirus in your home

Calicivirus has no outer fatty envelope, which makes it resistant to many everyday cleaners. ABCD recommends disinfectants based on sodium hypochlorite (bleach), potassium peroxymonosulfate or chlorine dioxide, or a product approved as effective against norovirus, a close relative of FCV. Check the label for a claim against feline calicivirus or norovirus. For outbreaks, ABCD also lists accelerated hydrogen peroxide, a commercial disinfectant of the kind your vet clinic or shelter may use. It is not the household hydrogen peroxide sold in pharmacies.

For a simple home option, Cornell's Baker Institute says: "A dilute bleach solution made up of one half cup of bleach per gallon of water is effective at killing the virus."

How to use it well:

Clean first. Wash away food, litter, saliva and discharge with detergent and water, then disinfect. Disinfectants work poorly on dirty surfaces.
Give it time. Leave the disinfectant wet on the surface for the contact time on the product label before rinsing.
Treat what the cat touched: bowls, litter boxes, carriers, hard floors and surfaces.
Hot-wash fabrics. ABCD advises washing bedding and similar items at 60°C (140°F) or hotter.

Cleaning lowers the amount of virus around the house, but a carrier cat keeps shedding it. That is why cleaning protects new arrivals best when it goes with vaccination and careful introductions.

Vaccination: what it can and can't do

Calicivirus is a core vaccine: the 2020 AAHA/AAFP Feline Vaccination Guidelines recommend it for every cat, alongside feline herpesvirus 1, panleukopenia and rabies (and FeLV for cats under a year old). It usually comes as one combination vaccine with herpesvirus and panleukopenia.

For pet kittens, the US guidelines outline:

A first dose no earlier than 6 weeks of age, then repeat vaccinations 3 to 4 weeks apart until 16 to 20 weeks of age
A booster between 6 months and 1 year of age (the guidelines suggest considering 6 months)
After that, a booster every 3 years

ABCD advises yearly boosters for cats in higher-risk situations, such as boarding catteries and multi-cat homes. Your vet will set the schedule for your cat's lifestyle. Readers in Europe can compare our vaccination schedule for cats in Europe.

Be realistic about what the shot does. It usually protects against disease, not infection: a vaccinated cat can still catch calicivirus and shed it, but tends to get much milder signs. Because the virus mutates constantly, no vaccine covers every strain, and ABCD suggests asking your vet about switching vaccine strains if fully vaccinated cats keep getting sick. Cats that have already had calicivirus should still be vaccinated, since one infection does not protect against all strains.

Ginger cat being given a vaccine injection by a veterinarian — Calicivirus is part of the core combination vaccine recommended for every cat.

Protecting the other cats in your home

Separate the sick cat and give it its own bowls, litter box and bedding. Handle it last and wash your hands afterwards.
Keep vaccines up to date for every cat in the home.
Quarantine new cats. ABCD suggests three weeks apart before introducing a new cat to a calicivirus-free household, with the option to swab for FCV first. Cornell suggests one to two weeks of watching for signs. Ask your vet which fits your situation.
Take extra care with kittens, seniors and cats with other illnesses, which tend to get sicker.

What about the rest of the family? People cannot catch feline calicivirus: Cornell and ABCD agree it poses no threat to humans. ABCD adds that calicivirus-like viruses have only rarely been found in dogs and probably play no significant role there, so your dog is not considered at risk.

Questions to ask your vet

Is this calicivirus, herpesvirus, or both? Is a test worth doing?
How do I know if my cat is eating and drinking enough, and when should I call back?
Should my other cats be tested, separated or given a booster?
Is my cat likely to become a carrier?
Which vaccine schedule fits my cat's lifestyle?

FAQ

How long is a cat with calicivirus contagious?

For as long as it sheds the virus, which is often a month or more after it looks well (see carriers above). Before bringing a new or unvaccinated cat home, ask your vet whether a swab test makes sense.

Can a cat get calicivirus twice?

Yes. Immunity after infection does not last for life and does not cover all strains, which is why vets still vaccinate cats that have recovered.

Can indoor cats get calicivirus?

Yes, though the risk is lower. The virus can come in on hands, clothes and objects, or with a new cat. Indoor-only cats with little contact with other cats may be candidates for less frequent boosters; your vet will decide.

Can humans or dogs get calicivirus from cats?

People cannot. FCV belongs to the same virus family as human norovirus, the stomach bug, but it does not infect humans. Dogs are not considered at risk either.

Originally written by Dr. Catharina Hjorth. Updated by the I Love Veterinary editorial team.

Sources

This article is for general information and is not a substitute for advice from your veterinarian.