Feline calicivirus (FCV), in the Caliciviridae family, is one of two important viral causes of respiratory infection in cats. FCV can be isolated from around 50 percent of cats with upper respiratory infection.
The various strains of FCV vary in virulence. Since it is an RNA virus it has a high elasticity of its genome which makes it more adaptable to environmental pressures. This causes the development of vaccines more difficult. In infected cats it has been shown that the gene for the major structural protein of the viral capsid evolves through immune-mediated positive selection.
One form of FCV was found to cause a particularly sever systemic disease in cats. The disease is contracted by viral invasion of epithelium and endothelium and secondary host immune response. The first description of the virus was done in 1998 in Northern California. In private households FCV is present in about 10 percent of cats while in shelters the percentage is closer to 25-40.
After replicating in the oral and respiratory tissues FCV is secreted in saliva, feces, urine, and respiratory secretions. It can be transmitted through air, orally, and on inanimate objects. The virus is usually shed by infected cats for about two weeks.
Symptoms may develop acutely, chronically, or not at all. Subclinical infections often result in symptoms when the cat is stressed. Symptoms include fever, conjunctivitis, nasal discharge, sneezing, and ulceration of the mouth. Pneumonia may also develop. Stomatitis and polyarthritis can develop without any upper respiratory infection symptoms, but fever and loss of appetite may occur. Symptoms vary so widely due to the virulence of different strains of the virus.
VS-FCV has a mortality rate up to 67 percent. Symptoms are similar to non-lethal cases but can include fever, edema of the limbs and face, jaundice, and multiple organ dysfunction syndrome.
Without specific tests FCV is hard to diagnose since it is similar to other feline respiratory diseases. Stomatitis may indicate FCV. Along with a hard diagnosis there is no specific treatment for FCV. Antibiotics treat secondary bacterial infection. Rehydration and nursing care are used to treat dehydration. Stomatitis, although difficult to treat, is approached with antibiotics, corticosteroids, and tooth extractions which have all been met with varying success.
CaliciVax is the only licensed vaccine for prevention of VS-FCV. Quarantine is the best control of FCV in catteries and kennels. It is highly contagious and hard to contain. It can survive several days up to weeks in a dry environment and longer in a cooler environment.