What is Calicivirus in Cats?
Feline calicivirus is a common respiratory infection in cats that is often acute but can become chronic. It is a highly contagious virus that spreads through saliva, nasal secretions, and infected surfaces. Feline calicivirus usually causes mild flu-like symptoms but can be fatal in some cases.
Specifically, feline calicivirus is an RNA virus that belongs to the family Caliciviridae. There are actually numerous strains of feline calicivirus, which can make creating an effective vaccine challenging. Some strains cause more severe disease than others. The virus infects and replicates in the oral cavity, upper airways, lungs, joints, and epithelial tissue.
According to the Cornell Feline Health Center, feline calicivirus is one of the most common causes of upper respiratory infections in cats. The virus compromises a cat’s immune system, leaving them vulnerable to secondary infections which can become quite severe. While many cats recover, the virus remains dormant and may reactivate periodically.
The manifestations of feline calicivirus can range from mild symptoms like sneezing and runny eyes, to oral ulcers, limping, and severe pneumonia. In rare cases it can even be fatal, especially in very young or immunocompromised cats. Thankfully, most cats fully recover and the disease remains relatively mild. But even after recovery, cats remain carriers of the virus. There is no known cure for feline calicivirus, only supportive treatment and prevention through vaccination (https://www.vet.cornell.edu/departments-centers-and-institutes/baker-institute/our-research/feline-calicivirus).
How Does Calicivirus Affect Cats?
Feline calicivirus causes respiratory infections in cats. Early symptoms include fever, lethargy, runny nose and eyes, sneezing, and oral ulcers on the tongue, hard palate, and lips (Hurley, 2004).
The infection can progress to pneumonia, lameness, and chronic stomatitis (inflammation of the mouth). The mortality rate is typically less than 10%, but can reach 45% in chronic cases (Bordicchia et al., 2021).
Is Calicivirus Fatal for Cats?
Calicivirus infections are not always fatal for cats, but some highly virulent strains can lead to high mortality rates. One strain, known as Calicivirus Strain FCV-Ari, has been associated with mortality rates up to 60% in infected cats according to research (Pedersen et al., 2000).
Fatal cases of calicivirus usually involve secondary bacterial infections that lead to pneumonia. The viral infection damages the respiratory tract lining, allowing opportunistic bacteria to take hold and cause pneumonia. This often leads to death in cats infected with virulent calicivirus strains (Pedersen et al., 2000).
Kittens and cats with compromised immune systems are at highest risk for severe disease and death from calicivirus infections. Their immature or weakened immune responses have more difficulty fighting off the virus and secondary infections (Feline Calicivirus Overview).
How is Feline Calicivirus Transmitted?
Feline calicivirus is highly contagious and spreads easily between cats. The primary route of transmission is through direct contact with infected saliva, nasal secretions, or ocular discharges from an infected cat (1). This commonly occurs when infected and susceptible cats interact closely, such as when grooming each other, sharing food bowls or bedding, or through bites and scratches.
Indirect transmission also readily occurs when susceptible cats come into contact with surfaces, objects, or materials contaminated with the virus. Shared food and water bowls, toys, litter boxes, and bedding harbor the virus and can serve as fomites facilitating spread (2). The virus can survive in the environment for several weeks under optimal conditions.
Aerosol transmission is also possible, especially in confined spaces where cats congregate closely like shelters and multi-cat households. When an infected cat sneezes or coughs they generate aerosolized droplets containing the virus which can be inhaled by nearby cats (2).
Feline calicivirus is very contagious and cats in groups or those with outdoor access are at highest risk. Isolating infected cats and practicing good hygiene helps curb transmission.
Diagnosing Feline Calicivirus
Clinical signs are usually sufficient for a veterinarian to make a presumptive diagnosis of feline calicivirus infection. The oral ulcers, nasal discharge, fever, and lethargy are characteristic of this viral disease in cats. In many cases, testing is not required to confirm the diagnosis and begin appropriate treatment.
If desired, there are some laboratory tests that can identify the calicivirus. PCR testing of oral or conjunctival swabs can detect the presence of viral nucleic acids, confirming an active infection. Serology testing of blood samples can identify antibodies produced by the cat in response to calicivirus exposure and infection. Increased antibody levels indicate the cat’s immune system is fighting the virus.
According to veterinary experts at Cornell University’s College of Veterinary Medicine, “In most cases, there is no need to make a definite diagnosis, as these infections are common and will resolve with supportive treatment.”1 Looking for clinical signs is typically sufficient for diagnosing feline calicivirus.
Treating Cats with Calicivirus
Unfortunately, there is no specific antiviral treatment for feline calicivirus infections, so vets mainly provide supportive care to treat symptoms and keep the cat comfortable while its immune system fights the virus 1. This usually involves:
- Administering antibiotics if secondary bacterial infections develop
- Giving anti-inflammatory medication to reduce fever, pain, and inflammation
- Providing intravenous or subcutaneous fluids if the cat is dehydrated
- Offering nutritional support if eating is painful
With prompt veterinary attention and supportive care at home, most cats recover fully within 1-2 weeks. However, the virus never truly goes away and can reactivate later in life if the cat experiences stress or immune suppression 2.
Preventing Calicivirus in Cats
Vaccination is recommended as part of the core vaccine protocol for cats by veterinary associations like the American Association of Feline Practitioners (AAFP). Kittens should receive an initial series of vaccines starting as early as 6-8 weeks of age, with boosters every 2-4 weeks until 16 weeks of age. After completing the kitten series, adult cats need ongoing boosters to maintain immunity according to the vaccine manufacturer’s recommendations (typically every 1-3 years) [1]. Since calicivirus mutates frequently, broad-spectrum vaccines that protect against multiple viral strains are preferred.
During outbreaks of virulent systemic calicivirus infections, infected cats should be immediately isolated from other cats to prevent transmission. Thorough cleaning and disinfection of the environment is necessary as the virus can persist in the environment. Bleach solutions, accelerated hydrogen peroxide, and potentiated quaternary ammonium disinfectants are effective against calicivirus [2].
Routine biosecurity measures are always advised for multi-cat households and catteries, including quarantining new arrivals, maintaining cleaning protocols, and minimizing fomite transmission between cats.
Outlook for Cats with Calicivirus
The prognosis for cats infected with calicivirus is generally good. According to Cornell University’s College of Veterinary Medicine, most cats recover fully within 1-2 weeks with supportive care at home, such as appetite stimulants, fluids, and medications for pain relief 1.
However, the virus can persist long-term in recovered cats. These chronic carrier cats may have recurrent oral ulcers and shed the virus when stressed. Thankfully, fatal pneumonia is an uncommon outcome except in rare virulent systemic outbreaks 2.
Overall, with supportive care at home and follow up exams as needed, most cats go on to make a full recovery from calicivirus within a few weeks. However, chronic ulcers and viral shedding are possible long-term outcomes.
Euthanasia Considerations
Euthanasia is not generally recommended for cats with calicivirus except in severe, advanced cases with a poor prognosis (1). Kittens with overwhelming systemic disease that is unresponsive to treatment may also be considered for euthanasia as a humane option (2). However, euthanasia should not be the first choice. Palliative care options such as pain management, hydration therapy, nutritional support, and nursing care should be exhausted first to provide the cat with the best quality of life possible (3). The decision for euthanasia should be made carefully based on the cat’s individual condition and prognosis. Calicivirus infection alone is not a valid reason for euthanasia, as many cats can live happily with the virus when properly managed.
Sources:
(1) https://www.abcdcatsvets.org/guideline-for-infectious-diseases-in-shelter-situations-and-their-management/
(2) https://catvets.com/public/PDFs/PracticeGuidelines/RetrovirusGLS-Summary.pdf
(3) https://www.abcdcatsvets.org/guideline-for-feline-calicivirus-infection/
Key Takeaways
Feline calicivirus is a common infection in cats, but the mortality rate is generally under 10%. While calicivirus can occasionally be fatal, particularly in very young or immunocompromised cats, the vast majority recover fully with proper care and do not experience severe illness. Vaccination protects most healthy cats from developing the more serious effects of calicivirus infection.
The key to managing calicivirus is prompt veterinary care to prevent or control secondary bacterial infections, provide supportive care, and relieve symptoms. With appropriate treatment, the prognosis for cats infected with calicivirus is good. Even in severe cases that become system-wide, healthy adult cats are expected to make a full recovery with no lasting effects once the infection has run its course.
While feline calicivirus sounds alarming, it is an extremely common viral infection in cats. With proper preventative care through vaccination and quick veterinary treatment if infected, the vast majority of cats go on to live normal, healthy lives without any major complications from calicivirus.
