• Along with the rhinotracheitis virus, feline calicivirus (FCV) is responsible for most feline upper respiratory infections.
  • Cats that go outside or spend time around other cats are at increased risk for exposure to FCV infection.
  • Vaccination can protect cats from disease associated with FCV.

What Is Calicivirus?

Feline upper airway infections, sometimes called upper respiratory infections, are very common. They resemble the common cold in people and are characterized by clinical signs such as sneezing, wheezing, and discharge from the eyes and nose. Along with the rhinotracheitis virus, feline calicivirus (FCV) is responsible for most feline upper respiratory infections.

Calicivirus is highly contagious among cats but is not contagious to humans. There are several types of FCV, and the severity of illness they cause can vary.

How Do Cats Become Infected With Calicivirus?

Calicivirus is spread among cats through respiratory secretions (mucus and droplets from the nose and mouth) and discharge from the eyes. Most commonly, infection is spread by direct contact with an infected cat that is sneezing. However, FCV can live in the environment for weeks, and contaminated food and water bowls, litterboxes, and other items can help spread the virus.  Fortunately, FCV can be killed by cleaning contaminated areas with a dilute bleach solution.

Some cats that recover from FCV become carriers of the virus. This means they can infect other cats even though they don’t appear to be sick themselves.

Because FCV is highly contagious, easily spread, and has a carrier state, it can be difficult to eliminate from a multicat household or from a group of cats that goes outside and can be exposed to other cats.

What Are the Signs of Calicivirus?

The most common clinical signs of FCV are associated with the upper respiratory infection that the virus tends to cause. However, young or very sick cats can develop more serious complications. Clinical signs include the following:

  • Ulcers in the mouth and on the tongue
  • Gingivitis (inflammation of the gums)
  • Sneezing and congestion
  • Open-mouthed breathing
  • Lethargy (tiredness)
  • Red, runny eyes
  • Runny nose
  • Loss of appetite

In some cases, the respiratory infection associated with FCV can progress to severe pneumonia. Also, FCV-associated mouth and tongue ulcers are very painful, causing some cats to refuse to eat or drink.

One type of FCV, called virulent systemic calicivirus (VS-FCV), causes more serious clinical signs and can cause death in more than 30% of infected cats. Clinical signs associated with VS-FCV include those of other FCV strains, with the addition of more severe complications:

  • Fever
  • Edema (fluid accumulation under the skin) of the face and legs
  • Ulcers, sores, and hair loss on the face and feet
  • Difficulty breathing
  • Vomiting and diarrhea
  • Limping

VS-FCV was first reported in the late 1990s and occurred as outbreaks at animal shelters and catteries. Fortunately, the virus does not seem to be spreading to the general cat population.

How Is Calicivirus Diagnosed and Treated?

Sophisticated testing of body fluids can be used to diagnose FCV infection, but most veterinarians make the diagnosis based on clinical signs. No medication can cure FCV. Treatment is mainly supportive and consists of administering fluids to combat dehydration, offering soft food until mouth ulcers heal, administering antibiotics to help treat secondary bacterial infections, and prescribing other medications as needed to help control other clinical signs.

How Can Calicivirus Be Prevented?

Several vaccines are available for preventing disease associated with FCV. There is also a vaccine against VS-FCV. All of the available FCV vaccines have been tested and found to be safe and effective when administered as directed.

The FCV vaccination is recommended for all cats. Kittens are generally vaccinated around 8 to 9 weeks of age (depending on vaccine label recommendations). Booster vaccinations are given 3 to 4 weeks later, followed by additional boosters every 1 to 3 years.

Cats that go outdoors, live with other cats, or visit grooming or boarding facilities are at greater risk for exposure to FCV compared with cats that stay indoors and have limited contact with other cats.

Keeping the environment clean can help prevent the spread of FCV. Be sure to wash your hands after handling an infected cat. Similarly, bowls, blankets, towels, toys, litterboxes, and other items should be cleaned with a dilute bleach solution (if possible) to reduce the risk of further disease spread. Keeping sick cats separated from healthy cats can reduce the likelihood of spreading FCV.

Any new kitten or cat being introduced into the home should be examined by a veterinarian as soon as possible and separated from all other household pets for a quarantine period of at least a few weeks. Any problems or signs of illness should be reported to your veterinarian before introducing the new cat to your other pets.

If your cat is known or suspected to be infected with FCV, contact your veterinarian promptly to discuss how you can protect your other pets.