Lesions produced by feline picornaviruses of different virulence in pathogen-free cats

Capsid protein genetic analysis and viral spread to the spinal cord in cats experimentally infected with feline calicivirus (FCV)

We investigated primitively the molecular basis of the neural spread of a feline calcivirus isolate (FCV-S) from the spinal cord of a cat that died after manifesting excitation. Experimental infections of cats with three clones from parent virus isolate FCV-S, isolated based on plaque size, were performed, and virus recovery from the spinal cord and the nucleotide and predicted amino acid sequences of the viral capsid protein region (ORF2) were compared. In the experimental infection with the one-time cloned virus (C1L1) isolated from a large plaque, the C1L1 was recovered from the spinal cord. In contrast, seven-times cloned C6L7 (from large plaque) and five-times cloned C5S2 (isolated from small plaque) were not recovered from the spinal cord. Genetic analysis of the capsid protein gene of the three viral clones revealed that four bases were different and two amino acids were different at positions 34 (Val in C6L7 and Ala in C1L1 and C5S2) and 46 (Leu in C6L7 and Pro in C1L1 and C5S2) between C6L7 (with large plaque) and C5S2 (with small plaque). The amino acid at position 434 of C1L1 was different from those of C6L7 and C5S2 (Gly in C1L1, D (Asp) in C6L7 and C5S2). From these results, the plaque size seemed not to be related to the spread of virus to the spinal cord. Clone C1L1, which spread to the spinal cord, had a difference of one amino acid from the other two clones, which may be related to the ability to spread to the spinal cord.

Chronic oral infections of cats and their relationship to persistent oral carriage of feline calici-, immunodeficiency, or leukemia viruses

Two hundred and twenty-six cats from the Veterinary Medical Teaching Hospital (VMTH), a cat shelter, and a purebred cattery were tested for chronic feline calicivirus (FCV), feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) infections. Chronic oral carriage of FCV was present in about one-fifth of the cats in each of the groups. FIV infection was not present in the purebred cattery, was moderately prevalent (8%) in the pet population of cats examined at the VMTH for various complaints and was rampant in the cat shelter (21%). Unexpectedly high FeLV infection rates were found in the hospital cat population (28%) and in the purebred cattery (36%), but not in the cat shelter (1.4%). FCV and FeLV infections tended to occur early in life, whereas FIV infections tended to occur in older animals. From 43 to 100% of the cats in these environments had oral cavity disease ranging from mild gingivitis (23-46%), proliferative gingivitis (18-20%), periodontitis (3-32%) and periodontitis with involvement of extra-gingival tissues (7-27%). Cats infected solely with FCV did not have a greater likelihood of oral lesions, or more severe oral disease, than cats that were totally virus free. This was also true for cats infected solely with FeLV, or for cats dually infected with FeLV and FCV. Cats infected solely with FIV appeared to have a greater prevalence of oral cavity infections and their oral cavity disease tended to be more severe than cats without FIV infection. FIV-infected cats that were coinfected with either FCV, or with FCV and FeLV, had the highest prevalence of oral cavity infections and the most severe oral lesions.

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.

Induction of immunity to feline caliciviral disease

Six specific-pathogen-free cats were exposed by aerosol to a feline calicivirus of low virulence (F-9 virus). Homotypic (anti-F-9) seroconversion occurred in all cats by postexposure day 14. The serum of one cat on postexposure day 14 and four of six cats on postexposure day 35 neutralized feline picornavirus isolate no. 225 (FPV-255), a virulent feline calicivirus. Homologous antiviral activity was detected before the appearance of heterologous (anti-FPV-255) activity and always was present in higher titer. Protective immunity was evaluated on postexposure day 35 by aerosol challenge with FPV-255. The pyrexia, depression, dyspnea, oral ulcers, and severe pneumonia produced in two susceptible specific-pathogen-free cats by exposure to FPV-255 did not occur in the cats that had been infected previously with F-9 vir. The study demonstrates that heterotypic protective immunity to feline calicivirus disease can be induced by prior infection with feline calicivirus of low virulence.

Cross-protection among feline caliciviruses

Each of five groups of specific-pathogen-free and conventionally reared cats was infected with a different strain of feline calicivirus. Two of the strains were pathogenic, producing characteristically fever, depression, loss of appetite, buccal ulceration, and occasionally increased ocular and nasal secretion. Two of the other strains were midly pathogenic and associated with fever or buccal ulceration or both; the fifth strain was nonpathogenic. The two pathogenic strains plus three others shown also to be pathogenic were used 3 months after the initial infection to challenge the cats in rearranged groupings. Of the 28 conventional cats challenged six (21.4%) showed at least a febrile response, although none of the 30 specific-pathogen-free cats showed any clinical signs. After challenge, virus was recovered from throat swabs of 37 or the 58 cats (63.8%) including the six which showed symptoms, but the duration of the excretion of virus was significantly less than that seen with the initial infection. The homologous and heterotypic antibody responses correlated well with the clinical protection, or lack of it, seen on challenge. The results provide further evidence for significant cross-relationships between feline caliciviruses.