Feline Calicivirus Infections – Transmission, Symptoms, Diagnosis, and Prevention

Picture of spotted cat in living room

Feline calicivirus infections are caused by a virus that mostly affects the upper respiratory tract and oral cavity of cats. It’s one of the most contagious and dangerous medical conditions that affect cats, and it is also known as cat flu.

The virus exists all across the world and to date, there have been no measures taken to eradicate it. That’s why we recommend that you vaccinate your cat against the disease to help both prevent it and to avoid passing it on to other domesticated felines.

What Is Feline Calicivirus and How Is It Spread?

As we have noted in the beginning, this disease is highly contagious, and it’s caused by a small virus that affects the upper respiratory tract and triggers acute infections in that location. It’s also been associated with several other diseases.

The virus is typically transmitted from one cat to the next, but direct contact isn’t always required for it to be spread. The saliva and the nasal and ocular secretions of the infected cats are the main culprits, but the virus can also be found in sneeze droplets. Needless to say, it can get on your cat’s food bowl or litter tray, and from there, it can infect your other cat – if you have two, for example.

Another way that the virus can be spread is through the cat’s bedding or grooming aids. The worst thing about the pathogen, however, is the fact that it can survive without a host for as many as seven to fourteen days and in some situations, even a month in the cat’s environment.

How Long Does the Infection Last?

Calicivirus in cats has an incubation period of two to six days before the cat develops any symptoms. Uncomplicated infections can last for up to 21 days, but all of the cats that are infected will release the virus via their body secretions for around three weeks.

Some cats become carriers following the recovery from the disease, and some of them could transmit the virus to their peers for several months while others could remain a carrier for the remainder of their life. Female cats that are carriers can pass the infection to their newborns.

Clinical Signs

There are several strains of the virus that can be found out there, and some of them are more dangerous than others. That is why the clinical manifestations of the disease can differ largely depending on the strain that has infected the cat but also depending on the cat’s health status.

An infected cat can develop an acute upper respiratory infection, gingivitis and stomatitis, a virulent systemic FCV infection, or a limping syndrome. Naturally, all of these are characterized by different symptoms.

Acute URI is one of the most common manifestations of the disease. Most of the signs you’ll notice in an infected cat are nasal discharge, conjunctivitis, sneezing, ocular discharge, inappetence and fever, and ulceration of the tongue. The signs can last from a couple of days to a couple of weeks, and they can be more or less severe depending on a variety of factors. Young kittens can also develop pneumonia.

Gingivitis and stomatitis make another clinical sign, but it is often associated with the upper respiratory infection. The cat’s oral mucosa and gums turn red, and the animal has a very hard time feeding and drinking water. Sometimes, the lesions can be localized, and in other cases, they can spread to such an extent that they will cover the mucosa in the whole mouth.

Virulent systemic FCV infections are caused by very pathogenic strains of the virus, which have suffered mutations. These mutations allow the virus to affect various organs other than just the mouth and upper respiratory tract. If they are infected by one of these strains, cats can develop pneumonia, hepatitis, skin swelling and ulceration, pancreatitis, and bleeding from the intestine or the nose. Around half of the infected cats with such a strain do not survive.

Young cats can develop a rather unique clinical manifestation which consists of joint inflammation. Arthritis can affect the cat for several days only, but it can be very painful or uncomfortable, especially in kittens. This limping syndrome can evolve on an animal that also suffers from an acute upper respiratory infection.


If the cat has not been vaccinated and the vet notices the typical signs of a calicivirus infection (ulcers in the mouth), a presumptive diagnosis is often enough. A definitive one may be necessary in the case of breeding animals or if an individual cat is suffering from an infection and it doesn’t respond to treatment.

The diagnosis consists of the collection of cell samples and discharges (from the eyes, mouth, or nose) which are then sent to a laboratory where they are used for PCR, viral isolation, or immunohistochemical staining.

Should the infected cat have persistent respiratory symptoms, the veterinarian might have to take additional testing such as skull or chest X-rays, blood tests, or various sensitivity tests of the abnormal discharges.

Treatment and Disease Management

Many cats recover from the disease naturally, so your vet might prescribe anti-inflammatory medication or eye drops, as well as broad-spectrum antibacterial drugs to ensure that no secondary bacterial infection complicates the disease. Usually, cats also have to receive treatment to support their immune system, especially when they have persistent ulcers and feeding can be a problem.

The treatment also involves alleviating the symptoms of the upper respiratory infection (nasal or airway congestion), and if a cat is dehydrated, she has to receive fluids.

Nursing care is critical when it comes to a feline calicivirus infection. Some cats lose their sense of smell, and that is what could make them have a lower appetite. They might have to receive supplements or an appetite stimulant.

What’s also very important is for you to prevent the disease from being spread, especially if you have a cat colony you care for. Any cat that shows even the smallest clinical sign needs to be isolated and the living environment has to be cleaned and sanitized. Any implements, litter trays or feeding bowls also have to be sanitized, and the people coming in contact with the possibly infected cat have to wash their hands with care and use separate aprons or equipment.


Beginning with the age of 8 weeks, vaccination against this disease can be performed effectively. While some cats might still develop a mild form of the infection during their lifetime, it is almost impossible for them to be affected by the strains that could lead to life-threatening clinical manifestations. Because there are so many strains of the virus, the vaccine is a little less efficient compared to those types of vaccines against diseases where the virus has just one strain or compared to vaccines against bacterial diseases.

Many modern vaccines include more than one strain of feline calicivirus so as to offer a broad range of protection.

Other Cats and Your Family – Risks

First of all, we have to get something out of the way and it’s that feline calicivirus can affect cats and cats only, which is why it is not a disease that can be transmitted to humans. No people who share the same living environment with an infected cat can at any time develop the infection.

When it comes to other cats, however, we have already emphasized that this is a highly contagious disease, so you should do your best to isolate from the rest the one that you believe might have been infected. If you decide to a adopt a cat (especially a stray), always make sure you keep it apart from the others for as many as two weeks so as to assess any clinical signs that she might develop.



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