A herpes simplex virus type 1 mutant containing a nontransinducing Vmw65 protein establishes latent infection in vivo in the absence of viral replication and reactivates efficiently from explanted trigeminal ganglia.

Vmw65, a herpes simplex virus type 1 (HSV-1) tegument protein, in association with cellular proteins, transactivates viral immediate early genes. In order to examine the role of Vmw65 during acute and latent infection in vivo, a mutant virus (in1814), containing a 12-base-pair insertion in the Vmw65 gene, which lacks the transactivating function of Vmw65 (C. I. Ace, T. A. McKee, J. M. Ryan, J. M. Cameron, and C. M. Preston, J. Virol. 63:2260-2269, 1989) was examined in mice. Following corneal inoculation, the parental virus (17+) and the revertant (1814R) replicated effectively in eyes and trigeminal ganglia with 30 to 60% mortality. At either equal PFU or equal particle numbers, in1814 did not replicate in trigeminal ganglia and none of the infected mice died. Although in1814 did not replicate following corneal inoculation, it established latent infection in trigeminal ganglia. HSV-1 in1814 reactivated at explant as efficiently and rapidly as did 17+ and 1814R. Even low amounts of inoculated in1814 (10(2) PFU) were sufficient to establish latent infection in some animals. Since infectious in1814 was not detected at any time in mouse trigeminal ganglia, in1814 provided a unique opportunity to determine how soon after primary infection latency begins. Latent in1814 infection was detected shortly after virus reached the sensory ganglia, between 24 to 48 h postinfection. Thus, though Vmw65 may be required for lytic infection in vivo, it is dispensable for the establishment of and reactivation from latent infection. These data support the hypotheses that the latent and lytic pathways of HSV-1 are distinct and that latency is established soon after infection without a requirement for viral replication. However, the levels of Vmw65 reaching neuronal nuclei may be a critical determinant of whether HSV-1 forms a lytic or latent infection.