When to see a vet urgently
Contact a veterinary clinic immediately if respiratory or mouth symptoms are accompanied by any of the following:
- Breathing is difficult or your cat breathes with its mouth open.
- Your cat does not eat or drink because of mouth pain, and its general condition deteriorates.
- Your cat is unusually weak, collapses or becomes dehydrated.
- The face or legs swell, the skin ulcerates and your cat has severe signs of systemic illness.
You can find a vet near you. Tell the clinic about a suspected infectious disease before arriving so that other cats can be protected.
Overview
The pathogen is an RNA virus in the Caliciviridae family. It spreads easily between cats through the respiratory route, nasal, eye and mouth secretions, and contact with care equipment. The virus survives in the environment for a long time, making it particularly dangerous in crowded conditions. Cats that have recovered may remain long-term carriers and shed the virus intermittently.
A carrier cat may also shed virus continuously without noticeable symptoms. A cat that looks healthy can therefore be a source of infection, and the end of infectiousness cannot be inferred simply from a runny nose stopping. Assessing prolonged FCV shedding is part of the care plan, particularly in multi-cat environments.
The virus has no envelope, which partly explains its environmental resilience. Not all ordinary cleaning or disinfectant products work reliably against it. Secretions transferred on an object, hand or item of care equipment can maintain a chain of infection even if cats do not meet directly.
Causes
The main cause of the disease is infection with FCV. Infection spreads:
- through direct contact with an affected cat
- through shared food bowls, litter trays and toys
- through the respiratory route during sneezing
- on clothing and human hands through mechanical transfer
The risk of infection increases when several cats are kept close together and the same equipment is used for different cats. Separating symptomatic animals, providing separate feeding and care equipment, and cleaning hands help reduce spread. A vaccinated cat is also treated as potentially infected and shedding virus if it has symptoms or a known exposure.
Risk factors
Cats more susceptible to calicivirus include:
- kittens under one year old with a less developed immune system
- unvaccinated animals
- cats living in shelters and breeding catteries
- cats under ongoing stress
- animals with weakened immune systems following illness or with chronic conditions
A kitten's susceptibility does not necessarily mean it has an immune deficiency caused by disease. A kitten's protection and vaccination response change as it grows; antibodies received from its mother can interfere with vaccine effectiveness. Several vaccinations are therefore needed in the primary course. Adult and vaccinated cats can also become ill, although vaccination usually reduces disease severity.
Symptoms
Clinical signs depend on the viral strain and the state of the immune system:
- sneezing, a runny nose and nasal discharge
- watery eyes and conjunctivitis
- ulcers and erosions on the tongue, palate and lips
- drooling and loss of appetite due to pain
- fever
- lethargy and reduced activity
- lameness from temporary viral arthritis
⚠️ Severe cases, particularly in kittens, can develop pneumonia, airway ulcers, systemic disease and death.
Mouth pain can be the main symptom even when sneezing is minimal. Your cat may approach food but retreat, drool or stop chewing. A blocked nose impairs the sense of smell and can reduce interest in food. Simply offering a food bowl is therefore not always enough to restore eating.
Rare virulent systemic FCV disease must be distinguished from an ordinary upper respiratory infection. As well as high fever and poor general condition, it can involve swelling of the head and limbs, skin lesions, jaundice and severe respiratory symptoms. Suspected cases require urgent care and infection control. An ordinary positive FCV test does not, on its own, establish this form of disease.
Complications and consequences
Calicivirus infection can lead to:
- secondary bacterial infections, such as bronchitis and pneumonia
- chronic rhinitis and stomatitis
- weight loss due to poor appetite
- death in kittens and weakened cats
The association with chronic mouth inflammation does not mean every FCV-positive cat develops stomatitis or that the virus alone explains all persistent mouth problems. Ongoing pain when eating and mouth inflammation need their own investigation. Other respiratory pathogens may also be present, so one virus does not always explain the entire clinical picture.
Diagnosis at the vet
Diagnosis is based on:
- clinical signs, with mouth ulcers being a typical finding
- PCR testing of samples from the mouth and nose
- serological tests for FCV antibodies
- chest X-rays if pneumonia is suspected
PCR testing looks for viral genetic material in a sample. A positive result may be consistent with infection in a symptomatic cat, but also occurs in healthy carriers. Recent vaccination with a live-virus vaccine can also affect interpretation. The timing and site of sampling and the symptoms are considered alongside the laboratory result.
A negative PCR result does not reliably rule out FCV. The virus's considerable genetic variation and sample characteristics can affect detection. Decisions about isolation and treatment of a symptomatic cat may therefore need to be based on the overall assessment before results arrive or despite a single negative result.
Antibody measurement is not usually suitable for confirming acute FCV infection because antibodies are common after both previous infection and vaccination. Finding antibodies therefore does not show that current nasal signs or a mouth ulcer are caused by FCV. If pneumonia or persistent illness is suspected, the need for further investigations is also assessed separately.
Treatment and maintaining food intake
Treatment usually relieves symptoms and supports recovery. Your vet assesses mouth pain relief, hydration and nutritional intake. Breathing difficulties may require supplemental oxygen, and a weak or dehydrated cat may need hospital care. Home care is suitable only if your cat's condition and the practical delivery of treatment allow it.
An antibiotic does not eliminate calicivirus. One may be needed for a confirmed or suspected secondary bacterial infection, but an FCV finding alone does not automatically mean an antibiotic is necessary. A medicine intended for another respiratory infection does not necessarily treat FCV either. Medicines are selected according to symptoms and findings.
Offer soft, aromatic, slightly warmed food as advised by your vet. Nasal and eye secretions can be removed gently with a damp cloth. Monitor whether your cat eats enough, rather than simply whether it visits the bowl. If pain or another illness prevents adequate intake, your vet will plan the necessary nutritional support.
Limiting infection at home
Provide a quiet space for the affected cat, separate from other cats. Use separate bowls, a litter tray and care equipment. Attend to healthy cats before handling the ill cat, and wash your hands thoroughly. Infection can also travel on clothing, so consider changing and washing it according to the clinic's instructions.
Remove visible dirt and secretions before disinfecting. Choose a product with demonstrated effectiveness against non-enveloped viruses and follow the manufacturer's use and safety instructions. Rinse bowls and other washable equipment thoroughly where necessary and allow them to dry. Do not clean litter trays and food bowls at the same time in the same sink.
Plan the introduction of a new cat to a group carefully. A single test result or vaccination does not resolve infection control, as an animal without symptoms can also shed virus. If several cats become ill or symptoms are unusually severe, ask your vet for a plan covering the whole group.
Prevention
Vaccination offers the best protection. Preventive measures include:
- vaccination according to an individual plan recommended by your vet, with a kitten primary course and boosters tailored to infection risk; the vaccine protects against severe disease but does not always prevent infection
- quarantining new cats before introducing them to the group
- hygiene and disinfection
- minimising stress
- supporting the immune system through nutrition
The vaccination schedule is tailored to current guidance, the product used, your cat's age and infection risk. General schedules do not replace an individual plan, and a kitten's additional vaccination should not automatically be postponed. Your vet also assesses the reliability of previous vaccination records and the possible effects of maternal antibodies.
A previous infection does not guarantee protection against every FCV strain. A recovered cat's vaccination plan is also reviewed. Vaccination, cleaning and management of contacts are needed together, because the vaccine primarily protects against clinical disease and does not ensure that a cat cannot spread infection.
What it means for owners
Calicivirus is one of the most common contagious infections in cats. Remember that even mild cases need supportive care and attention. In severe cases the prognosis may be poor. Vaccination is the most effective way to protect your cat and reduce disease severity.
Note: this material provides general information and does not replace veterinary advice. Contact a vet immediately if symptoms appear.
Frequently asked questions
Can a vaccinated cat get calicivirus?
Yes. Vaccination usually reduces disease severity but does not reliably prevent infection or virus shedding. A vaccinated cat with symptoms needs the same assessment of its condition and infection control measures as other cats.
Does a positive PCR mean FCV is causing every symptom?
No. The result can also reflect carrier status, and several pathogens may be present at the same time. Your vet interprets the sample alongside symptoms, vaccination history and other investigations.
Does an antibiotic cure FCV infection?
It does not cure the viral infection itself. An antibiotic may be used if a bacterial infection complicates the situation. Pain relief and support for hydration and nutrition are often central to FCV care.
Is a cat that has recovered from nasal symptoms immediately non-infectious?
Not necessarily. Some cats continue shedding after symptoms improve, and shedding can persist for a long time. The need for isolation and protection of other cats is assessed with your vet.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- GUIDELINE for Feline calicivirus infection, European Advisory Board on Cat Diseases, accessed 2026-11-03.
- Feline Calicivirus, Cornell University Baker Institute for Animal Health, accessed 2026-11-03.
- Feline Calicivirus Infection, VCA Animal Hospitals, accessed 2026-11-03.
- Feline Respiratory Disease Complex, Merck Veterinary Manual, accessed 2026-11-03.
- 2024 guidelines for the vaccination of dogs and cats, World Small Animal Veterinary Association, accessed 2026-11-03.
- GUIDELINE for Control of infectious diseases in shelters, European Advisory Board on Cat Diseases, accessed 2026-11-03.