Studies on cytopathogenic viruses isolated from cats with respiratory infections. I

Neutralizing epitopes of feline calicivirus

A new collection of eighteen neutralizing monoclonal antibodies (N-MoAbs), raised against feline calicivirus (FCV), was used to analyze neutralizing epitopes of the F4 strain of FCV, the prototype strain of FCV in Japan. By cross-neutralization tests with the 20 FCV strains including Japanese. American, Swiss, and New Zealand isolates, the 18 N-MoAbs were categorized into six groups. One N-MoAb (1 D 7) neutralized all the strains tested: eight N-MoAbs neutralized only FCV-F 4; while the others neutralized the FCV strains in various degrees. In order to confirm this grouping, eight N-MoAbs were used to select neutralization-resistant variants of FCV F4. Although no variant against 1 D 7 was obtained, antigenic variants against other N-MoAbs were obtained. Neutralization tests using these variants revealed that there are six neutralizing epitopes on FCV F4 and that several epitopes are functionally related. One of these epitopes was the same epitope as one of the two epitopes identified by another panel of N-MoAbs we produced previously. Therefore, a total of seven neutralizing epitopes on FCV F4 were identified. Immunoblot analysis indicated that four of the seven epitopes existed on the 67 kDa capsid protein of the virus.

Pathogenicity of a strain of feline calicivirus for domestic kittens

A strain of feline calicivirus, isolated from a cheetah exhibiting ulcerative glossitis and conjunctivitis, was administered by aerosol to 4 domestic cats and by contact to a fifth cat. Despite the limited number of animals available for the experiment, the pathogenicity of the virus strain for domestic cats was established. In aerosol-infected animals, clinical signs were referable to infection of both upper and lower respiratory tracts. The virus produced an interstitial pneumonia which, early in infection, was uncomplicated by secondary bronchopneumonia. The in-contact cat exhibited clinical signs referable to infection of the oral cavity only and no lesions were noted in the lower respiratory tract at autopsy. Ulcerative glossitis was a feature of the disease in aerosol-infected and in-contact cats. The virus was isolated from the pharynx of all cats for up to 21 days after infection and from the tonsils at autopsy. The tonsils were considered to be a probable site of multiplication of virus in "carrier" cats.

Serological relationships among feline caliciviruses

A total of 46 strains of feline calicivirus isolates from the United Kingdom, United States, Australia, and New Zealand were used in an investigation of their serological relationships based on the serum neutralization test. Although demonstrable antigenic variation exists between these isolates, it is shown that significant in vitro cross-activity exists between all these isolates to greater or lesser extent. All isolates tested may be regarded as serological variants of a single serotype of feline calicivirus. It is postulated that this relationship would provide for considerable cross-protection during successive exposures of cats to various feline caliciviruses.