Feline Calicivirus in Cats: Causes, Symptoms, and Treatment

Feline calicivirus (FCV) is a highly contagious virus that most often causes sneezing, nasal and eye discharge, fever, and painful mouth ulcers. Many cats with uncomplicated infections recover with veterinarian-guided supportive care, but some strains cause far more serious disease. No specific antiviral treatment for FCV is available, so care focuses on keeping the cat hydrated and fed while the illness runs its course. Vaccination lowers the risk and severity of disease, but it does not guarantee that a cat will avoid infection.

What causes feline calicivirus and how it spreads

FCV is a calicivirus that shows wide genetic variation between strains, and that variation helps explain why illness ranges from a mild cold-like episode to severe disease. The virus is shed in oral and respiratory secretions. Cats catch it through direct contact with an infected cat, through contaminated objects such as shared bowls and grooming tools, and when people or handlers move between cats without changing contact or hygiene routines.

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Spread is greatest where cats are housed closely together. Shelters, breeding colonies, and multi-cat households carry the highest risk. Cornell University College of Veterinary Medicine reports that roughly 10% of cats housed in small groups become infected, compared with up to 90% in crowded conditions. These figures describe populations, not an individual cat’s chance of infection, and the Cornell page does not give a year for these estimates; it was accessed in 2026.

A cat can also remain a carrier. Some cats keep shedding FCV after they appear to have recovered, which means a cat that looks healthy can still expose others.

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Signs of calicivirus infection

The typical signs of uncomplicated FCV involve the upper airways and mouth:

• Sneezing and nasal congestion or discharge
• Eye discharge
• Fever
• Drooling
• Ulcers on the tongue or inside the mouth
• Lethargy and loss of appetite

Signs vary with the strain involved, so two cats with the same virus may not look identical. Infection can also cause a temporary shifting lameness, including in kittens, which owners sometimes mistake for an injury.

Complications to watch for

Respiratory disease can progress to pneumonia, and young kittens are at the greatest risk of this. Oral pain and loss of smell caused by congestion can make eating difficult, which in turn affects hydration and recovery. Some cats develop chronic gingivitis or gingivostomatitis, an inflammation of the gums and mouth lining that can persist beyond the acute illness.

How long illness lasts

Mild illness typically lasts 5 to 10 days. Severe cases can last up to six weeks. These durations come from general veterinary references and are not a guarantee for any one cat.

Rare severe systemic disease

A small number of cases involve a virulent systemic form of FCV, often called FCV-virulent systemic disease (FCV-VSD). This form can cause high fever, swelling of the head or limbs, skin lesions and hair loss, jaundice, and bleeding. It is far less common than ordinary respiratory disease, but it is the reason owners should not assume that every calicivirus infection will be mild.

Two Cornell sources give different fatality figures, and they should not be combined into one rate:

Both figures describe severe disease in the populations and settings those sources examined. Neither describes the typical cat with a mild respiratory infection.

How veterinarians diagnose calicivirus

Diagnosis usually starts with the history and physical examination. Oral ulcers combined with respiratory signs make FCV a likely suspect, but the picture is not specific. FCV can look very similar to feline herpesvirus and other causes of feline respiratory disease, and mixed infections are common. Appearance alone cannot always identify the cause.

When tests are used

Depending on the case, especially during outbreaks or when illness is complex, a veterinarian may use reverse-transcription PCR (RT-PCR) on oral or eye samples, or attempt virus isolation. These tests help, but they have limits that owners should understand before reading a result as a verdict:

• A positive PCR can reflect a carrier that is shedding virus rather than the cause of the current symptoms.
• A recent modified-live vaccination can affect results.
• A negative test does not always rule out FCV.
• Commercial testing does not reliably distinguish ordinary FCV strains from virulent systemic strains.

For these reasons, a result is interpreted alongside the cat’s signs, vaccination history, and exposure history.

Treatment: what helps and what does not

Treatment is mainly supportive. A 2022 review from the European Advisory Board on Cat Diseases (ABCD) states that specific antiviral treatment for FCV is not available. Supportive care is planned with a veterinarian, because the right approach depends on how much the cat is eating and drinking and how severe the signs are.

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Supportive care at home

1. Call your veterinarian before starting anything. Ask which home measures are appropriate for your cat’s age and condition.
2. Protect hydration and nutrition. Track how much water and food the cat takes each day. If the veterinarian agrees, offer warmed, soft, strong-smelling food, since mouth pain and congestion suppress appetite.
3. Clean discharge gently. Wipe the eyes and nose with a soft, damp cloth, one clean area per wipe, to keep crusting from blocking the airways and eyes.
4. Ask about congestion and pain relief. Cornell describes saline nebulization, mucolytics, and vaporizers for congestion, and the ABCD fact sheet lists saline nebulization and mucolytics. Use only what your veterinarian recommends.
5. Use antibiotics only under direction. They are given for suspected secondary bacterial infection or in severe cases. They do not treat the virus itself.

Hospital care for severe cases

Veterinary intervention is needed when a cat cannot maintain intake or becomes dehydrated. Hospital care can include feeding tubes and intravenous fluids. Severe systemic disease may require intensive veterinary care, and prognosis depends on how serious the illness is, the cat’s age, and whether complications develop.

Room humidifiers

A cool-mist room humidifier may make the air more comfortable for a congested cat. It is an optional comfort measure only. The sources do not test consumer room humidifiers, and none establishes one as FCV treatment. Humidified air does not replace nebulization or other care your veterinarian prescribes.

When to seek urgent veterinary care

Contact a veterinarian promptly for any respiratory sign. Seek urgent care without waiting if any of the following occur:

• Breathing is difficult or labored
• The cat cannot eat or drink
• The cat becomes markedly weak
• Swelling of the head or limbs, jaundice, or bleeding appears

This list is conservative guidance based on the complications described above. It is not a published triage protocol, so your veterinarian may advise differently for your cat.

Prevention through vaccination

FCV-containing vaccines are recommended for healthy cats. Vaccination reduces the likelihood and severity of disease. Because FCV varies between strains, a vaccine does not cover every strain, and vaccinated cats can still become infected and shed virus. Those limits are why vaccination works best alongside the household controls described below.

Vaccine timing depends on age, the product used, and exposure risk. The two European and US sources reviewed here do not give identical schedules:

Do not treat these schedules as a single prescription. Confirm timing with your veterinarian and the product label for the vaccine your cat receives.

Preventing spread at home and in multi-cat settings

Isolating a sick cat from others is the most practical step when you have more than one cat. Keep the affected cat’s bowls, bedding, and litter tools separate, and clean them before they are shared again.

Disinfectants matter because FCV resists many common products. Cornell notes that dilute bleach can be effective. The ABCD fact sheet lists these agents as effective against FCV:

• Sodium hypochlorite
• Potassium peroxymonosulphate
• Chlorine dioxide

Follow the product instructions for dilution and contact time, and keep cats safely out of the room while cleaning and ventilating. Wash your hands between handling cats, especially if you care for an infected cat and then touch others.

Shelters and breeding colonies should also follow veterinary cleaning guidance and consider the infection’s persistence in carriers when deciding how to move cats between groups.

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