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. Cheetahs are the other species of the family Felidae known to become infected naturally.
Clinical signs in cats infected with FCV may develop acutely, chronically, or not at all. Latent or subclinical infections often become clinical when the cat is stressed, such as at the time of adoption. Acute signs of FCV include fever, conjunctivitis, nasal discharge, sneezing, and ulceration of the mouth (stomatitis). Pneumonia may develop with secondary bacterial infections. In addition to stomatitis, some cats may develop a polyarthritis, both probably immune-mediated through immune complex deposition. Stomatitis and polyarthritis can develop without any upper respiratory infection signs, but fever and loss of appetite may occur. Less commonly, glomerulonephritis can develop in chronic cases secondary to immune complex deposition. The great variability of clinical signs in individual cases of FCV is related to the relative virulence of different strains of the virus.