Feline calicivirus (FCV) is a virus of the family Caliciviridae that causes disease in cats. It is one of the two important viral causes of respiratory infection in cats, the other being Felid alphaherpesvirus 1. FCV can be isolated from about 50% of cats with upper respiratory infections. FCV is highly contagious and can cause cats to develop mild to severe respiratory infections and oral diseases. Kittens and young adult cats are usually at the highest risk for infection, but a cat of any age can be affected. Some strains of calicivirus may cause an infected cat to develop sudden painful lameness in one or more joints, and there is one specific strain of feline calicivirus that causes severe generalized disease. The initial symptoms involve the eyes, nose, and mouth, but the infected cat quickly develops a high fever, severe depression, edema of the legs and/or face, jaundice, and symptoms of multiple organ disease. This strain is highly infectious, and the death rate is reportedly up to 67%.

FCV spreads through direct contact with saliva, eye discharge, nasal discharge, or aerosolized sneeze droplets from infected cats. Common ways a cat may become infected include direct contact with an infected cat, kittens born to an FCV-carrier mother, sharing food bowls, water bowls, or litter trays with an infected cat, contact with a human who recently interacted with an infected cat, and contact with contaminated environments and objects, including bedding or grooming tools. A cat that has a calicivirus infection will be infective to other cats during the incubation period and for at least 3 weeks after developing symptoms. A cat that is a carrier of calicivirus may always be infective to other cats.

Symptoms of FCV include sneezing, nasal discharge, conjunctivitis, oral ulcers, and fever. Cats who contract FCV-VSD may show the following signs: high fever, swelling of the head and legs, crusting sores around the face and mouth, hair loss around the nose, ears, eyes, and foot pads, skin. Most cats will recover from FCV in 7-10 days, but they can become carriers and shed virus from oral and nasal secretions long term. Cats that become chronic carriers may develop oral inflammation (gingivitis/stomatitis) and be at increased risk for growths in the nose, mouth, or ear (nasopharyngeal or aural polyps).

A vaccine called Calicivax™ is available that includes modified forms of a strain of FCV that causes FCV-VSD, and a typical strain of FCV[[2]](https://www.vet.cornell.edu/departments-centers-and-institutes/baker-institute/our-research/feline-calic...