Feline calicivirus (FCV) is a common virus that usually causes upper respiratory infections in cats, causing sneezing, runny nose and eyes, and sometimes painful sores inside the mouth or even sudden lameness. Upper respiratory issues occur fairly commonly in cats and are often caused by infectious diseases. This highly contagious disease can easily spread throughout a population of cats, making it a major problem in animal-shelter environments. Fortunately, although there is no direct cure for the illness, most cats recover completely with supportive care, although many will become asymptomatic carriers of the virus.

What Is Feline Calicivirus?

Feline calicivirus is a highly contagious viral pathogen that affects cats. It is part of a family of RNA viruses called Caliciviridae. Some other types of calicivirus can affect humans and other animals, but feline calicivirus strains will only affect cats.

FCV most commonly affects a cat's upper respiratory system and oral cavity. However, the virus can affect other systems in the body on occasion.

Typically, a cat that is exposed to the calicivirus will go through a two- to six-day incubation period before symptoms appear. Once the illness starts, it generally lasts for two to three weeks. The cat is contagious during this entire period. As many as 50 percent of infected cats will continue to carry the virus even after recovery, and this carrier stage can last from months to the rest of the cat's life. Although feline carriers of FCV often show no symptoms themselves, they are still contagious to other cats. Female cats carrying FCV can pass the disease to their kittens, as well.

Symptoms of Feline Calicivirus in Cats

A cat suffering from FCV generally has symptoms similar to those experienced by humans with a common cold. Stuffy nose, running nose and eyes, sneezing, loss of appetite, and a general malaise are most common, but with more severe infection, the cat can develop equally severe symptoms. Kittens and senior cats are more likely to experience severe illness than young adult or middle-aged cats.

Cats with calicivirus most commonly develop signs of upper respiratory infection, including discharge from the eyes and/or nose, and sneezing. Severe upper respiratory infections can progress to pneumonia.

Feline calicivirus may also cause cats to develop painful ulcers in the mouth, especially on the tongue. The pain may cause the cat to refuse to eat, and generally will cause the cat to drool, sometimes heavily. FCV is also associated with stomatitis, which is characterized by significant inflammation of the mouth and lips.

Lameness and fever occur in some cases of feline calicivirus. In addition, some cats may contract a more serious strain—called FCV-VSD—that causes a virulent systemic infection. This may affect the major organs and can lead to more serious issues like skin lesions and ulcers, loss of appetite, fever, and jaundice.

Feline calicivirus-related infections may be chronic in some cats. They may periodically experience flare-ups of symptoms.

It is possible for some cats to be carriers of feline calicivirus. These cats may show no signs of disease but can still transmit the virus to other cats.

What Causes Calicivirus in Cats?

There are several strains of feline calicivirus, all of which are highly contagious. A cat contracts FCV via direct contact with an infected cat's saliva, eye/nasal discharge, or aerosolized droplets from sneezes. The virus enters a cat's body through the nose, mouth, or eyes. Infected female cats can also pass the virus on to their kittens.

Feline calicivirus is most commonly spread in multi-cat environments. Animal shelters, pet stores, catteries, and boarding facilities are considered high-risk spaces, and as many as 40 percent of the cats housed in these high-density places may be carriers—and thus spreaders—of FCV.

Cats that have received all boosters of the FVRCP vaccine may have some immunity as the "C" in this vaccine stands for calicivirus. However, because there are multiple different strains of feline calicivirus, not all are covered in the vaccine. Vaccinated cats can still contract feline calicivirus, but they may experience milder symptoms.

How Do Vets Diagnose Calicivirus in Cats?

Generally, your veterinarian will diagnose your cat with FCV based on clinical symptoms, particularly if your cat has ulcers inside its mouth. Occasionally, however, a vet may decide to take a swab of secretions from the ill cat's mouth, nose, or eyes, and have it tested for the presence of the virus. If your cat develops lameness, the vet may order an x-ray as well to rule out other potential causes of the limp.

How to Treat Calicivirus

There is no cure for feline calicivirus, nor is there a specific treatment for this common disease. However, supportive treatment can help keep your cat more comfortable while it recovers, as well as prevent secondary bacterial infections, such as pneumonia.

Cats with mild to moderate upper respiratory infections will usually be sent home under your care. Your vet may prescribe nasal decongestants, eye drops to relieve ocular inflammation, and systemic anti-inflammatory drugs. Antibiotics may be prescribed to treat secondary infections. Nasal drops or nebulization may be necessary for cats with severe nasal congestion.

Cats with FCV often lose their appetite because they cannot taste or smell as well as usual. Plus, oral ulcers can make eating very uncomfortable for some cats. An appetite stimulant may be recommended if your cat is not eating well. It's important to feed strong-smelling foods that appeal to your cat, and soft food is best if oral ulcers have developed.

Cats with moderate to severe signs may require hospitalization for supportive care. These cats typically receive intravenous fluids to support hydration and injectable medications to manage symptoms. Breathing treatments may be necessary if the cat develops pneumonia. A feeding tube may need to be placed if your cat is not eating.

Prognosis for Cats with Calicivirus

Most cats will recover fully from FCV, although there is a good chance that they will become carriers of the virus for at least a short while. However, cats with the most severe form of the disease, FCV-VSD, have a poorer prognosis, with up to 60 percent succumbing to the disease.

How to Prevent Calicivirus

The best way to protect your cat from feline calicivirus is to vaccinate regularly. While the calicivirus vaccine will not fully prevent contraction of the virus, it will help your cat fight off the infection and experience milder symptoms. Your veterinarian might also recommend a booster if your cat will be spending time in a kennel, groomer, or other location with a high density of cats.

Cats with feline calicivirus should be kept separate from other cats to prevent the spread of the disease. Multi-cat environments should be cleaned thoroughly and routinely with pet-safe disinfectants to minimize accidental exposure.

And of course, it's always important to keep your cat in optimal health by feeding it a high-quality, balanced diet formulated specifically for cats, encouraging it to exercise regularly through play sessions, and scheduling regular veterinary checkups to ward off health problems before they turn serious.