Attempted immunization of cats with feline infectious peritonitis virus propagated at reduced temperatures

Abstract

Objective. To protect cats by inoculating them intratracheally with feline infectious peritonitis virus (FIPV), followed by a second inoculation with virus propagated at reduced temperatures. Animals. Twelve 12-week-old, specific-pathogen-free kittens. Procedure. Ten to 400,000 plaque-forming units (PFU) of virulent (low passage) FIPV, strain FIPV-1146 were inoculated intratracheally, followed by intranasal inoculation with high-passage FIPV-1146 (104 to 106 TCID50) on day 133. Cats were allotted to 2 groups and challenqe exposed on day 133 by aerosolization of either virulent FIPV-1146 or FIPV-UCD1. Results. Two of the 3 severely affected kittens, given 3 dosages intratracheally, were euthanatized. The third kitten recovered. A serologic response was not detected in cats inoculated with 100 PFU or less and in 1 of 2 cats given 1,000 PFU. Clinical signs of infection were not observed in surviving cats after intranasal inoculation with high-passage FIPV-1146 133 days after the initial dose. All cats seroconverted. Aerosol challenge exposure of all kittens with either virulent FIPV-1146 or FIPV-UCD1 caused no adverse effects except in kittens previously affected after the first inoculation. Residual lesions of FIPV were observed histologically. Conclusions and Clinical Relevance. There appeared to be a beneficial effect clinically by intratracheal/intranasal inoculation, but not complete protection, as observed histologically.