Feline caliciviral disease: experimental immunoprophylaxis.

An attenuated feline calicivirus (FCV) was administered intramuscularly to specific-pathogen-free cats. Vaccination did not cause signs of illness. Oropharyngeal replication of attenuated FCV was not detected, nor was there evidence of virus transmission to contact-control cats. Antiviral neutralizing antibody was present in the serum of all vaccinated cats 7 days after they were given the 2nd intramuscular dose of immunogen. Vaccinated and control cats were challenge exposed to aerosols of a virulent FCV strain. All controls developed severe pneumonia and died within 7 days after this challenge exposure. In the vaccinated cats, signs of illness were absent or minimal; pulmonary lesions were milder and less extensive than those in the control cats. Feline calicivirus was isolated from ocular, nasal, and oropharyngeal swabbings from both control and vaccinated cats after viral challenge. Results indicate protective immunity to FCV disease can be induced by intramuscular administration of an attenuated FCV.