Latent pseudorabies virus infection established at supraoptimal temperature.

Little or no infectious virus was recovered from BHK-21 cells adapted to 40 degrees C, when they were infected with an attenuated strain of pseudorabies virus (PRV) at low multiplicity of infection (MOI) and subsequently kept at 40 degrees C. By passaging the infected cells at 40 degrees C, infectious virus disappeared within 2-3 passages. When the cells were shifted down to 37 degrees C, activation of virus growth occurred after a latent period of 48-72 hr. Infected cells kept at 40 degrees C were as sensitive to superinfection with the virulent PRV strain TOP as the control cells. The ability of PRV strains to enter into the described latent state was related with the degree of their virulence. When cells were treated with 5-bromo-2-deoxyuridine (BUdR) at 40 degrees C for 24 hr and then shifted to 37 degrees C, a slight increase in the number of infectious centres was observed and the latent period was also prolonged.