Calicivirus in Cats: Everything You Need to Know

A common viral infection in our feline friends, Feline Calicivirus (FCV), is prevalent within the UK, with incidences varying by region. It is highly infectious and can cause a wide range of symptoms. This article focuses on providing owners with general information and discusses the disease's transmission, diagnosis, management, and prognosis.

Though the Calicivirus vaccine is one of the core vaccines in the UK, many cats live with the disease. Recent research from the BSAVA found that a whopping 13.3% of cats were carriers of FCV, making it the most prevalent upper respiratory tract pathogen found.

What is Calicivirus in Cats?

Calicivirus is a contagious infection that easily passes from cat to cat and causes signs affecting the oral cavity and respiratory tract. The severity of the signs ranges from mild to severe, and it is even possible to be a carrier of the virus with no signs whatsoever.

Virus Characteristics

Belonging to the Caliciviridae family, this single-stranded RNA can frequently mutate. This means there are many strains, all with varying virulence.

As it is a ‘non-enveloped’ virus, it is not always easy to remove from the environment and can live on surfaces for weeks. However, it can be effectively cleaned by using bleach.

Transmission (How Cats Get Infected)

Cats can directly infect each other via their body fluids, by sneezing or coughing airborne droplets on each other. Often, when cats spend time together or groom each other, the disease will be spread.

This virus can also spread indirectly via objects contaminated with fluids like saliva. This means that things like water bowls and toys can indirectly transmit the viral infection. Even human hands can spread Calicivirus from one cat to another when stroking them.

Unlike Feline Immunodeficiency Virus (FIV), this virus is not typically spread via cat bites, fights, or sexual contact.

Common Strains of Calicivirus

One of the best-known strains is the FCV-F9 strain, which is traditionally included in vaccinations.

However, some companies will consist of other strains, such as FCV 255, in their vaccines to enhance protection.

Different Strains of the Virus

As there are several different virus strains, all of which can mutate, vaccines will never be 100% effective. Even so, a vaccine that contains the F9 strain should help to keep at least 87.5% of cats protected from the disease.

Vaccinations should generally slow down the transmission of the disease and can ensure that an infected cat does not become as unwell as one who has not been vaccinated. So, even though vaccines won’t always completely prevent the disease, they’re still worth getting.

Mutation and Variability

As with most RNA viruses, FCV mutates frequently. This is one of the main reasons it is so difficult to prevent this respiratory infection completely and why it continues to thrive within the UK population.

When an RNA virus replicates, there is no ‘editing’ or ‘proofreading’ system, so these mutations remain. New mutations are not recognised by antibodies and are not always covered by vaccines. With different strains come viruses of different strengths and virulence, some of which will cause more aggressive symptoms.

Risk Factors of Calicivirus

Not every cat is as susceptible to Calicivirus, and if a group of cats is exposed to an infected patient, only some of them will contract the virus.

Age, Environment, and Other Contributing Factors

Young kittens are at the highest risk, as their immune system is developing, and they’ll have little to no antibody protection. This is especially true if their mother has not been vaccinated or infected and they’ve not been consuming the antibodies in her milk.

Stress certainly plays a role in the contraction of FCV and other infectious diseases. A stressed immune system is less able to fight off the infection.

Cats who go outside and/or contact several other cats will also be at higher risk of meeting a carrier of FCV.

Multi-Cat Households or Shelters

The closer a cat has contact with an infected one, the more likely it is to become unwell. This means that places where more cats are naturally going to be together (like shelters and catteries) are more susceptible to FCV outbreaks.

Symptoms and Signs of Calicivirus

FCV causes many signs, and which of these develops will depend on the strain of FCV and the individual's immune status.

This is why the symptoms of one infected cat can look completely different from those we see in another.

Respiratory Symptoms

Calicivirus is frequently referred to as ‘cat flu’ and so it will be no surprise that some of the more common symptoms we see include:

• Nasal discharge: It may become cloudy and green, mainly if a secondary bacterial infection occurs.
• Sneezing: Though every cat will sneeze from time to time, those with FCV sneeze repeatedly.
• Coughing: A cough won’t always be present but can occur when the airways are inflamed. Cat owners often mistake coughs in cats as gags or retches.
• Hoarseness: The swelling in their throat can result in these cats losing their voice.
• Pneumonia (in the more severe cases): Those who develop pneumonia will be unwell and need veterinary attention.

Oral Symptoms

Some cats develop oral ulcers, gingivitis, or stomatitis (FCGS). This inflammation within the mouth inevitably causes trouble eating and pain. You may notice your cat drools, has bad breath, and develops discoloured fur and crusting around its mouth.

When you look inside the mouth, the tongue and gums can look angry, red, and swollen and sometimes, there may even be localised areas of bleeding.

Ocular Symptoms

Some cats have severe ocular symptoms, to the point where they struggle to keep their eyes open and have thick, gunky discharge.

Many will develop conjunctivitis, and some will also be dealing with eye ulcers.

Other Possible Signs

Some kitties will also have a fever, lethargy, and weight loss in addition to the symptoms discussed above.

Severity and Complications

Though most cats can cope with this virus without becoming too unwell, some may struggle with the symptoms and need to be hospitalised.

Pneumonia

It is rare for FCV to go into the lungs and cause pneumonia, but this is seen in the more severe cases.

You may notice your cat has laboured breathing and gets quickly breathless. In this instance, don’t hesitate to contact an emergency vet.

Limping Syndrome

Some variants of FCV can cause temporary joint inflammation and lameness, but this is not commonly seen. Thankfully, the signs are usually short-lived, resolving within a week.

Chronic Carriers

Up to about 40% of cats become carriers of FCV. They act as reservoirs of the virus, infecting other cats they come into contact with. Carriers may shed the virus for weeks or even months.

It is not common for cats to be lifelong carriers, which is more likely in immune-suppressed people.

Diagnosis and Testing for Calicivirus

Knowing if your cat has FCV is essential for them and for other cats with whom they may come into contact.

Clinical Examination

After a physical exam, vets will be suspicious of Cat Flu, as infected kitties tend to present with classic symptoms. A kitten who comes in with runny eyes and nose will always make a vet think of FCV.

Laboratory Tests

Not every cat will be tested to confirm the infection, as it takes time to get results and is costly. There are several available tests, including blood tests (ELISA or IFA) and oral or nasal swabs.

Differential Diagnosis

FCV has signs similar to other respiratory infections, including Herpes Virus, Mycoplasmosis, and Chlamydia. It is important to remember that respiratory infections often occur together, so diagnosing one doesn’t always mean that another is not present.

Treatment and Management for Calicivirus

How you support your cat will depend on how severely they are affected, whether or not they have other underlying medical issues, and your financial situation.

Supportive Care

The mainstay of treatment from home is supportive care. This includes things like offering tempting food that is easy to eat, maintaining good hydration, cleaning away crusting and discharge, and keeping the home warm.

Medications

Medications won’t always be necessary but will sometimes be required. Those with secondary bacterial infections should be given antibiotics, and patients may also benefit from anti-inflammatories and pain relief. For those with stomatitis, Interferon may be considered.

Home Care Tips

As many cats develop congestion, a reduced sense of smell, and oral inflammation, it is not unusual to see an appetite dip. It helps to offer a range of their favourite foods, such as mashed chicken, sardines, or eggs. Warming them up to release the aroma and offering the food from your hand can work well.

For cats not keen on drinking, consider adding warm water to their meals or offering rehydration solutions or cat soups.

Long-Term Management for Calicivirus

Not every cat requires long-term management; some will recover quickly and need no extra help.

Monitoring Chronic Carriers

Certain things can help those who do remain carriers. These include a high-quality diet rich in omega-3 fatty acids, antioxidants, and probiotics.

Regular vet checks are essential to monitor general health and assess for flare-ups or secondary infections.

Preventive Measures for Calicivirus

Though Calicivirus cannot always be prevented, there are things we can do to reduce the chance a cat becomes infected.

Vaccination

Every kitten in the UK should be vaccinated, and the vaccine course usually starts at nine weeks of age. These vaccines are then boostered every year.

While vaccines can’t 100% guarantee a cat won’t develop Calicivirus, the production of neutralising antibodies reduces the risk dramatically.

Hygiene and Isolation

Hygiene and isolation protocols are most important in places with multiple cats, such as rehoming centres. When you take home a new cat, isolating it from other cats for several weeks is sensible to ensure it does not begin to show signs.

After touching a cat, especially one who may be unwell, you should wash your hands well with warm, soapy water. This is particularly true if you’ll soon be touching your own cat.

Regular cleaning with bleach-based solutions can help remove the virus from surfaces.

Reducing Stress

Where possible, reduce stress and stabilise your cat’s home and routine. Stress can cause a flare-up of signs and may trigger viral shedding.

Females who are pregnant or nursing are under a lot of stress, so this is a standard time of viral flares. Neutering of affected cats is strongly advised.

Prognosis and Recovery

The strain of the virus a cat is infected with, whether or not it was vaccinated, and how unwell it becomes will dictate its prognosis and recovery.

Recovery Timeline

On average, a cat is unwell for a couple of weeks. Cats become most unwell by about day 4-5 but start to recover just a few days after this. For those with more severe cases or who develop pneumonia, recovery can take many weeks longer.

Factors Affecting Prognosis

An array of factors affect the prognosis, including the viral strain, vaccination status, age, and general health of the patient. For those who contract secondary infections, the prognosis can become more complicated.

Follow-Up Care

After diagnosis, you’ll want to monitor closely for any flare-ups and ensure your cat is coping well. Look for any trouble eating, flu-like symptoms, or new fevers. Have their vet assess your cat if they become unwell, informing them of their prior Calicivirus diagnosis.

Learn More About Calicivirus in Cats

Don’t hesitate to contact us if you’ve got questions or concerns surrounding Feline Calicivirus and your cat.

We’ve got plenty of experience when it comes to Cat Flu and can guide you on how best to care for your much-loved pet.

FAQs

Can humans catch calicivirus from cats?

No. Feline calicivirus is species-specific and cannot be transmitted to people. Although it spreads quickly among cats, no evidence suggests it causes human illness. Pet owners need not worry about contracting FCV themselves, but they should keep their pets vaccinated and maintain good hygiene practices to minimize the spread of this virus among cats.

How effective is the vaccine?

The vaccine against FCV is highly effective, significantly protecting most vaccinated cats. Studies show that it prevents severe disease in roughly 90% of felines receiving initial shots and regular boosters. While no vaccine provides absolute immunity, vaccinated cats typically display milder symptoms than those who remain unvaccinated.

Is calicivirus life-threatening?

In general, FCV is not considered life-threatening. Most infections involve mild to moderate upper respiratory symptoms—such as sneezing, nasal discharge, and mouth ulcers—that can be managed with proper veterinary care. However, severe or virulent strains of FCV can lead to pneumonia or other complications, especially in kittens, elderly cats, or those with compromised immune systems.

If a cat shows signs of difficulty breathing, high fever, or refusal to eat, prompt veterinary attention is crucial to prevent serious outcomes.

Can diarrhoea and vomiting be caused by FCV?

FCV typically targets a cat’s respiratory system rather than its digestive tract. Diarrhoea in cats is more commonly linked to factors like dietary changes, stress, parasites, or bacterial infections. Similarly, cat vomiting is usually triggered by abrupt diet changes, ingestion of inappropriate materials, or secondary health issues.

However, in rare cases, a highly virulent strain of FCV could affect multiple organ systems and potentially result in gastrointestinal symptoms. If a cat experiences persistent diarrhea or vomiting, it’s essential to seek veterinary advice for an accurate diagnosis and appropriate treatment.