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.
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