The effect of supraoptimal temperature on the formation of pseudorabies virus particles.

Replication of virulent and attenuated strains of pseudorabies virus (PRV) at supraoptimal temperature was inhibited in L cells non-adapted to 40 degrees C. Electron microscopy revealed the prevalence of hollow core particles without nucleoid; both the nuclei and cytoplasm of L cells were markedly altered at supraoptimal temperature. In BHK-21 cells adapted to 40 degrees C only replication of attenuated strains was inhibited whereas the virulent ones reached high titres at this temperature. The particles produced at 40 degrees C by attenuated strains were non-infectious but morphologically normal. The ability of attenuated PRV strains to reproduce in adapted BHK-21 cells at 40 degrees C was in correlation with the degree of their attenuation. Changes in the nuclei and cytoplasm of adapted BHK-21 cells at supraoptimal temperature were not as marked as in L cells.