Characterization of an attenuated temperature sensitive feline infectious peritonitis vaccine virus.

Intranasal administration of a ts-FIPV vaccine protected cats against two rigorous challenges of immunity. Investigations showed that ts-FIP viral RNA synthesis was normal at 39 degrees C and structural proteins were synthesized, but not expressed at the cell surface. Lack of surface expression combined with decreased virus titer indicate that, although structural viral proteins were initially synthesized, they were not packaged into intact virions at the nonpermissive temperature. The ts-FIP vaccine virus was shown to replicate exclusively in the upper respiratory tract, where lower temperatures allow maturation of the virus. Viral proteins expressed on cells in the upper respiratory tract probably stimulate the development of local IgA and CMI responses and a systemic CMI response which in turn may stop the dissemination of virulent FIPV if it crosses the mucosal barrier. Investigations are ongoing to study the protective mechanism of ts-FIPV induced immunity.