Lesions Produced by Feline Picornaviruses of Different Virulence in Pathogen-Free Cats

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Abstract
Sixteen pathogen-free cats were exposed by aerosol to either of two feline picornavirus isolates. The isolates used were picornavirus-255 and kidney-cell-degenerating virus. These viruses were selected to represent picornavirus prototypes of high and low virulence, respectively. Picornavirus-255 consistently produced depression, anorexia, and pneumonia. There were no lesions in the upper respiratory tract or conjunctiva, nor were there clinical signs of upper respiratory disease. The pulmonary lesions began as multifocal exudative pneumonia that progressed rapidly to interstitial pneumonia characterized by marked adenomatoid proliferation of pneumocytes. Three weeks after exposure the pulmonary lesions were principally resolved. It also produced discrete lingual and palatine ulcers that were easily detected. Experimental infection with kidney-cell-degenerating virus resulted only in transient fever and tiny vesicles and ulcerations of the lingual and tonsillar mucosae that could easily escape detection. No significant respiratory lesions were induced by kidney cell degenerating virus.