One key feature of feline calicivirus (FCV) is its antigenic and genetic variability-it is a highly adaptable virus. In the 1980s, a different presentation of FCV started to emerge. The outbreaks begin quickly and usually occur in environments in which there are large numbers of cats. Clinical signs include pyrexia; cutaneous edema; ulcerative dermatitis (including pad and ear lesions); anorexia; jaundice; bronchointerstitial pneumonia; and necrosis of the liver, spleen, and pancreas. Up to 50% of cats die or are euthanized. This syndrome is referred to as FCV-associated virulent systemic disease (VSD). In VSD, each of the FCV strains differs and it is believed that VSD is caused by viral mutations. Most of the outbreaks have been associated with introduction of cats from large rescue organizations or shelters. This may be an important part of the pathogenesis of the disease: High levels of replication of normal FCV strains may be needed to trigger outbreaks of VSD. FCV is also associated with chronic oral disease-lymphoplasmacytic gingivitis stomatitis. In some studies up to 80% of cats with this oral disease have been found to be shedding FCV. It can survive for up to two weeks in the environment and it can be transmitted via contact with contaminated environments in addition to cat to cat transmission. FCV has been isolated from feces and urine. Cleaning to remove gross debris and disinfection with household bleach are commonly recommended.

COMMENTARY: This is a great review article. The most important take-home point is that each outbreak of FCV has arisen independently, and that the viruses are not particularly more closely related to each other than they are to other milder variants of calicivirus. In other words, a vaccine against virulent calicivirus may not be especially likely to protect against other virulent calicivirus mutants, although it may protect against calicivirus in general (virulent or otherwise). In addition, although the risk for virulent systemic FCV is low, it is constant. FCV exists wherever cats are found and is especially common in cats from a multiple-cat background. Wherever FCV exists, there is a risk that a hypervirulent strain will develop. I often get questions from practitioners about whether virulent systemic FCV has been seen in their area and expressions of concern when it has been reported elsewhere in the state. As this article makes clear, these factors are irrelevant to the risk in a particular clinic. Unlike, say, canine flu, virulent systemic FCV is not spreading in a geographic fashion. Clinicians also need to realize that the pathogenicity of a particular strain cannot be determined by evaluating the signs in a single patient-cats showing mild signs of illness can transmit a virus that is fatal to another cat, and vice versa. Therefore, all cats showing signs of FCV, such as oral ulceration, should be handled with due infectious disease precautions. Extra care should be taken when handling cats from high-risk backgrounds, such as a rescue or multiple-cat household.

Feline calicivirus. Radford AD, Coyne KP, Dawson S, et al. Vet Res 38:319-335, 2007.