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Feline Calicivirus is a common respiratory disease which is highly infectious in cats.

Feline Calicivirus (FCV) and Feline Herpesvirus (FHV) are both viruses which cause the “Cat Flu” with widespread inflammation of the upper respiratory tract, leading to nasal secretion, sneezing, eye discharge, fever, loss of appetite and occasional limping in kittens.

Calicivirus is infectious and predominantly seen in unvaccinated cats, in shelters, catteries and boarding facilities, where many cats live in large colonies under stressful conditions.

Calicivirus can occur at any age; however, it tends to appear in kittens following the decrease of maternal antibodies (kittens over six weeks), including elderly and immunosuppressed cats (cats with FIV or FeLV infection) seem most susceptible.

Although a vaccine against Calicivirus similar to the kennel cough vaccination for dogs exists for cats, repeated yearly vaccination against FCV does not guarantee more protection since Calicivirus mutates quickly.

What is Feline Calicivirus and How Does It Spread?

Feline Calicivirus is a virus that causes acute upper respiratory infections in felines, although it’s linked to other illnesses.

The virus quickly spreads between felines when an infected cat sneezes. The droplets containing the virus particles fall onto the ground, contaminating the substrate it lands on. An infected carrier can transmit FCV through shared food dishes, water bowls, litter trays, and beds. The virus can also spread via direct cat-to-cat contact by transferring feline-infected saliva and eye or nasal discharge onto another cat.

FCV can survive seven days to a month in a contaminated environment like bedding or grooming equipment; therefore, regular cleaning and disinfection are vital to treating infected cats to prevent transmission.

Therefore, if you find a stray or feral cat outdoors, take it to the vet for a thorough health check or quarantine it to minimise exposure to unknown diseases to other pets.

Calicivirus Symptoms

The symptoms of FCV infection differ considerably from cat to cat. Some felines display mild and temporary symptoms, while others may exhibit severe upper respiratory illnesses.

Typical Calicivirus clinical signs include:

  • Upper respiratory infection – runny nose, sneezing, eye discharge, drooling and conjunctivitis (pinkeye). Lethargy, fever and inappetence due to loss of smell. Cats can develop tongue, gums, and lips ulceration in severe cases. Symptoms can last from a few days to weeks and differ in severity. Young kittens can also get pneumonia.
  • Stomatitis and Gingivitis – some cats will develop Stomatitis and chronic Gingivitis, which causes inflammation and thickening of the gums, making it painful for a cat to eat.
  • Arthritis (joint inflammation) – occasionally, kittens or young cats infected with FCV may temporarily display arthritis lasting a few days. The kitten or cat may have painful joints and exhibit lameness. This transitory immobility associated with FCV has acquired the terminology ‘limping syndrome’.
  • Virulent systemic FCV infection – in rare cases, the Calicivirus can manifest as a contagious systemic FCV infection, a much more pathogenic strain of FCV called vsFCV. These are linked with the virus mutation infecting different organs and the cells that line blood vessels. vsFCV can lead to severe disease, including pneumonia, pancreatitis, hepatitis (liver inflammation), skin ulceration and blood loss from the nose and intestines.
How is Calicivirus Diagnosed

If your cat shows signs of respiratory disease, it’s imperative to take them to the veterinarian.

Your vet will conduct a thorough physical exam, including a complete blood count and a urinalysis. They might also take swabs from your cat’s eyes, nose or mouth, which the vet will send to the laboratory to test for the virus. Veterinary labs distinguish the presence of FCV in two ways: 1. By growing the virus in culture. 2. Through a molecular procedure that detects the genetic material specific to Calicivirus called a Polymerase Chain Reaction (PCR) test.

An FCV antibody titre test will also be required to assess the level of Calicivirus antibodies in your feline’s system. Finally, your vet may take a chest x-ray to check your cat’s lungs and to rule out pneumonia.

Calicivirus Treatment Options

Most cats affected by the Calicivirus have mild infections and only require supportive care at home without veterinary intervention. However, severely affected kittens or cats who develop dehydration or pneumonia must be hospitalised and placed on intravenous fluid therapy.

Felines recovering from Calicivirus infection require excellent nursing care. Wipe away eye and nose secretions using damp cotton wool, while steam inhalation or nebulisation application with colloidal silver for those with severe nasal congestion is best. At the same time, immunostimulants like olive leaf extract may also be helpful. Keeping your cat warm and comfortable is also essential.

Secondary bacterial infections frequently complicate FCV infections, so your vet may suggest antibiotics to reduce the damage the infection causes.

Since most cats infected with FCV lack appetite, mainly due to fever, pain from oral ulcers, and sometimes because of their loss of smell, encourage your cat to eat by warming up their food, offering them smelly food (fish in oil, bone broth or lightly cooked chicken) or tempt your cat to eat from your hand. Cats who refuse to eat for three days will require hospitalisation to receive nutritional support and IV fluids.

Prevention of Feline Calicivirus

Preventing your cat from contracting FCV can be challenging since the Calicivirus is highly infectious, and healthy cats can carry this disease. You can minimise exposure by doing the following.

Vaccinating against FCV

Vaccination for Feline Calicivirus combined with Feline Herpesvirus and Feline Panleukopenia vaccine is recommended in kittens, starting around 8 weeks, followed by a second vaccine at 12 weeks, a third at 16 weeks old and a further booster every 1 – 3 years unless they are in a risked multi-cat environment.

Vaccination doesn’t prevent FCV infection but will significantly reduce infection severity, including clinical signs. While there are many strains of the Calicivirus, it’s challenging to design a vaccine that will protect all variants against them. Some newer vaccines combine multiple varieties of FCV to provide more comprehensive protection.

Preventing FCV Spread in Multi-Cat Households

FCV is highly prevalent in multi-cat environments. Special measures are necessary to prevent and reduce FCV-associated problems in multiple cat households, like decreasing cat group sizing, reducing introductions of new cats, separating sick cats, and vaccination, including disinfection against FCV.

If your household contains several cats with one or more infected with FCV, it’s vital to minimise the spread of the infection to other cats. Ideally, the sick cat should be quarantined in a single, easy-to-disinfect room (avoid carpet or soft furnishing). The room must contain clean food dishes, water bowls, a litter tray and any other items infected with the virus. Disinfect the relevant areas only with a cleaning solution that contains Sodium hypochlorite (bleach-based) disinfectant. However, be careful since most solutions irritate cats with immediate contact with the disinfectant.

Final thoughts

Most cats contracting the Calicivirus virus have symptoms similar to a bad cold. Nearly all felines will recover in about one week. However, in severe cases, it can take up to a few weeks for your cat to completely heal.



Care, I. C. (2018, August 17). Feline CaliciVirus (FCV) Infection. Retrieved February 20, 2023, from Icatcare: Feline CaliciVirus (FCV) Infection

Dr. Pete Wedderburn, D. (2023, February 16). Calicivirus In Cats: Causes, Symptoms, & Treatment. Retrieved February 28, 2023, from Cats.com: https://cats.com/Calicivirus-in-cats

Margie A Scherk, R. B. (2013). DISEASE INFORMATION FACT SHEET Feline calicivirus. Journal of Feline Medicine and Surgery, 15. Retrieved February 25, 2023

Hofmann-Lehmann R, Hosie MJ, Hartmann K, Egberink H, Truyen U, Tasker S, Belák S, Boucraut-Baralon C, Frymus T, Lloret A, Marsilio F, Pennisi MG, Addie DD, Lutz H, Thiry E, Radford AD, Möstl K. Calicivirus Infection in Cats. Viruses. 2022 Apr 29;14(5):937. doi: 10.3390/v14050937. PMID: 35632680; PMCID: PMC9145992 .





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