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What is feline calcivirus?

What is feline calicivirus? It 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”. It causes 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 feline immunodeficiency virus or feline leukemia virus infection).


Although a calicivirus vaccine (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.


The virus can survive seven days to a month on surfaces like bedding or grooming equipment; therefore, regular cleaning and disinfection are vital to treating infected cats to prevent transmission.



Calicivirus Symptoms

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


Typical 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, calicivirus can manifest as a contagious systemic infection, a much more pathogenic strain of FCV called vsFCV. These are linked with the virus infecting different organs and the cells that line blood vessels. This 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. 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.


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, one by growing the virus in culture and two through polymerase chain reaction (PCR), a molecular procedure that detects the genetic material specific to the virus.



Calicivirus Treatment Options

Most cats affected by 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 the infection require excellent nursing care to wipe away eye and nose secretions with a damp cotton ball. Using steam inhalation or nebulisation application with colloidal silver for those with severe nasal congestion is useful. 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 virus is highly infectious, and healthy cats can carry this disease. You can minimise exposure by doing the following.


Vaccinating against FCV

Vaccination for 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.


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


Preventing FCV Spread in Multi-Cat Households

Calicivirus 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 with a suitable cleaning solution such as Safe4 plus. Safe4 Plus has been especially formulated to kill feline calicivirus in just 30 mins of contact.


Most cats contracting calicivirus have symptoms similar to a bad cold and 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.


Written for Pet Life by Melina Grin (Vet Nurse)

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