Feline calicivirus is a respiratory virus found in almost all cats and kittens. It is one of several viruses included in routine kittenhood and adult vaccination programs. The virus causes an upper respiratory disease characterized by sneezing, watery nasal discharge, limping, and occasional fever. Calicivurus infections often cause painful ulcerations in the mouth, particularly on the hard palate and tongue. Afflicted cats don't eat because of the pain and inability to smell their food. In rare cases, a secondary pneumonia may develop. Calicivirus infection is not usually fatal, except in very young kittens that become very dehydrated and are unable to eat for several days. Once the virus has infected the tissues of the respiratory tract, normally harmless bacteria that live on these tissues begin to proliferate and cause disease. The watery discharge becomes thicker and opaque. Conjunctivitis may be a secondary problem.
Treatment includes oral and topical antibiotics, fluids, force feeding, and rest. Vaccination is highly effective in controlling the disease. Although it is not 100% effective in prevention, the disease is not as severe in cats that have been properly vaccinated. Kittens and cats that have been vaccinated can still get the disease if they are exposed to a large dose of the virus while being stressed or housed together with infected animals. Once over the initial infection, most cats become chronic carriers who can pass the virus on to kittens. They can have an occasional mild form of the disease.