Feline Calicivirus: When Your Cat’s Cold Can Cause Much Bigger Problems

It’s calicivirus, not Khaleesi virus! And while it may seem like a cold at first, it can cause severe illness in your pet. Here’s how to treat and prevent it.
Rhiannon Koehler DVM By Rhiannon Koehler, DVM, MPH Medically Reviewed by Michelle Moyal, DVM Updated January 06, 2023 Medically Reviewed by Michelle Moyal, DVM Advertisement Pin FB More Tweet Email Send Text Message Print
woman holding siamese cat in her arms; feline calicivirus Credit: Daily Paws / Jason Donnelly

The virus often spreads from cat to cat in crowded areas (such as shelters and multi-cat facilities). In its most severe and rare form, calicivirus—pronounced like "Khaleesi virus"—can limit cats' mobility and cause hospitalization or even death. Thankfully, an FCV vaccine limits the harm, and there's plenty you can do to protect your cat.

Here, find out what FCV is, how it's diagnosed, and what treatment looks like.

What Is Feline Calicivirus?

Feline calicivirus is one of the most common causes of upper respiratory infection in cats. Although any cat can contract FCV, it typically causes more severe infections in kittens or young adult cats. Calicivirus in cats is widespread and found across the globe.

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Causes of Feline Calicivirus

Calicivirus is highly contagious and mutates quickly. The virus is spread in secretions from the eyes or nose of an infected cat. Cats spread the virus when they play with or groom one another; share bowls; or contact items that may have these secretions on them, including your hands. Calicivirus can also spread in the air when an infected cat sneezes or coughs (although these signs are less common to see).

Signs of infection typically show up two to 14 days after exposure (most commonly within 3-4 days). Cats spread the virus for around two or three weeks after they're infected, but some cats become lifelong carriers and may intermittently shed the virus.

The risk of contracting calicivirus increases in crowded areas like animal shelters, multi-cat homes, and community cat colonies. Cats are also at a higher risk if they're stressed, have a suppressed immune system, or already have other upper respiratory pathogens like feline herpesvirus.

Symptoms of Calicivirus in Cats

Most commonly, calicivirus affects cats' upper respiratory tract and mouth. Signs include:

Discharge from the eyes or nose
Sneezing
Swelling of the pink tissues around the eye (conjunctivitis)
Holding one or both eyes partially shut
Poor appetite
Drooling
Bad breath
Sores in the mouth or on the hairless skin of the nose (nasal planum)

Occasionally, calicivirus causes pain in the joints, resulting in febrile limping syndrome. Cats with this form of calicivirus limp and may hesitate to walk. In kittens, limping syndrome typically occurs after upper respiratory signs or after vaccination (more on that below).

Calicivirus symptoms can persist from five to 10 days in mild cases and up to six weeks in more severe ones. Some cats develop lasting inflammation in their mouth (chronic stomatitis) that requires lifelong management.

Very rarely, calicivirus mutates to a highly fatal form called virulent systemic feline calicivirus (VS-FCV). VS-FCV is more likely to result from big outbreaks in crowded housing situations in which the mortality rate may be as high as 67 percent. In this form, symptoms include:

Severe upper respiratory signs or respiratory distress
Severe ulceration in the mouth, on the nose, paw pads, ears, and around the eyes
Swelling in the head and limbs
Yellowing of the eyes and skin (jaundice)
Bruising on the skin

Diagnosis of Calicivirus in Cats

Your veterinarian will consider calicivirus the most likely cause of an upper respiratory infection if your cat also develops ulcers in the mouth or on the nose. Medical staff may also use a special stain to check for ulcers on the surface of your pet's eyes (corneal ulcers).

If you want a definitive diagnosis, a laboratory can test swabs of the inside of the eyelids and the back of the throat. If your cat is limping, your veterinarian may suspect limping calicivirus syndrome if your cat is young, has a fever, and recently had upper respiratory signs.

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Feline Calicivirus Treatment

For most cases of feline calicivirus, treatment aims to relieve respiratory and oral discomfort. Because of the likelihood of secondary bacterial infections, cats with calicivirus often get prescribed antibiotics to take by mouth. They may also have you clean their eyes and nose routinely and prescribe antibiotics to put in the eyes if they have eye infections.

If your cat has significant congestion, your veterinarian may prescribe a nebulizer to deliver a fine mist to break up respiratory secretions. Another at-home option is to take your pet into the bathroom, shut the door, and turn the shower on warm for 10-15 minutes to create steam for your cat to inhale.

Some cats may require fluid support to prevent dehydration. In mild cases, the veterinarian may give the fluids under the skin and can often show you how to do this at home. If intravenous fluids are needed, your pet will stay in the veterinary clinic.

For ulcers in the mouth, your veterinarian may prescribe oral pain medications or topical medications that are meant to coat the ulcers and relieve pain. Because the ulcers cause pain and the congestion affects your cat's sense of smell, they may need appetite stimulants or a temporary feeding tube in severe cases. At home, you can offer them strong-smelling canned food and heat it up in the microwave to enhance its smell. If your pet doesn't eat for more than two days, go to your veterinarian right away.

Limping kitten syndrome is typically self-limiting, but prescribed pain medications may help your cat feel better.

Cats with VS-FCV will require hospitalization for aggressive supportive care and isolation from other cats (isolation should be considered in all cases of calici if possible).

How to Prevent Calicivirus in Cats

The feline calicivirus vaccination is considered a core vaccine for cats. While vaccination doesn't prevent infection, it can reduce the severity and length of the disease. Importantly, vaccination doesn't protect against VS-FCV.

Keeping your pet indoors and away from crowded housing situations is a great way to prevent calicivirus, especially VS-FCV. When bringing a new cat into your home, you should keep them separate from your resident cats for one or two weeks while monitoring for symptoms. Make sure to wash your hands before handling your cat if you've been interacting with other cats.