A new mutation of the calicivirus has been identified in various outbreaks in cats. The first outbreak was in California, but outbreaks have since been identified across the United States. The calicivirus in these cases seems to have mutated to a more virulent form, and is therefore now known as virulent systemic feline calicivirus (VS-FCV).
The virus may be shed in feces, sloughed skin and hair, and nasal, ocular, and oral secretions. Asymptomatic and mildly affected cats may transmit the fatal disease to other cats; therefore, all exposed cats should be considered a potential infectious risk. This virus is very contagious and easily spread by both direct contact and on clothes, dishes, bedding, and other objects. Strict hygiene is required to stop the spread in outbreaks.
Along with respiratory signs, cats will show a high fever, edema of the face and limbs, and ulceration and hair loss on the face, feet, and pinnas. There may also be other signs seen with more typical feline upper respiratory diseases, including nasal and ocular discharge, oral ulceration, anorexia, and depression.
A secondary immune response is believed to be responsible for the organ damage that accompanies these signs, and leads to a 60 percent fatality rate. The mortality rate is higher in adults than it is in kittens.
Although this syndrome remains uncommon, occasional outbreaks and clusters of cases have been documented throughout the United States. So far, this has occurred in cats of all ages, including those vaccinated for the common calicivirus as well as nonvaccinates. No other species is known to be affected by this strain of calicivirus. There is no known risk to human health.
Treatment: For affected cats, treatment consists of supportive care, along with drug therapy using steroids and interferon. Bovine lactoferrin may be useful. The efficacy of these treatments is not yet known.
Prevention: Isolate all cats suspected of being infected. VS-FCV can survive up to four weeks in the environment and is resistant to some disinfectants, but a bleach solution (diluted with water at 1:32) has been used to effectively contain previous outbreaks. All surfaces should be thoroughly cleaned and disinfected. Do not introduce any new cats for at least four weeks.
A new vaccine from Fort Dodge Animal Health, called CaliciVax, has recently been licensed for control (see page 108).
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"