HIGH-DOSE OCULAR INFECTION WITH A HERPES-SIMPLEX VIRUS TYPE-1 ICP34.5DELETION MUTANT PRODUCES NO CORNEAL DISEASE OR NEUROVIRULENCE YET RESULTS IN WILD-TYPE LEVELS OF SPONTANEOUS REACTIVATION

We report here that in the rabbit ocular model of herpes simplex virus type 1 (HSV-1) latency, spontaneous reactivation of the HSV-1 ICP34.5 deletion mutant d34.5 increased significantly in response to increasi ng infectious doses. At the highest infectious dose of d34.5, the spon taneous reactivation rate was indistinguishable from that of wild-type virus (average spontaneous reactivation rates for d34.5, 0.3 to 1.4% at 2 x 10(5) PFU per eye, 3.4% at 2 x 10(6) PFU per eye, and 6.3 to 11 .5% at 1 x 10(8) PFU per eye; average spontaneous reactivation rates f or marker-rescued virus, 7.7 to 19.6% at 2 x 10(5) PFU per eye). The p ercentage of latency-associated transcript (LAT) RNA-positive neurons in sections from trigeminal ganglia (TG) of rabbits latently infected with d34.5 demonstrated a similar dose-response effect as estimated by in situ hybridization (0.05% LAT RNA-positive neurons at 2 x 10(5) PF U per eye and 0.1% LAT RNA-positive neurons at 1 x 10(8) PPU per eye; P = 0.002). In contrast, even at the highest infectious dose (1 x 10(8 ) PFU per eye), d34.5 was less virulent (23 of 23 survivors) than the normal infectious dose (2 x 10(5) PFU per eye) of marker-rescued virus (14 of 27 survivors; P < 0.0001). In addition, at 1 x 10(8) PFU per e ye, d34.5 produced virtually no corneal disease, compared with the pro duction of severe corneal disease by 2 x 10(5) PFU of marker-rescued v irus per eye (P < 0.0001). Thus, at increasing infectious doses of d34 .5, both spontaneous reactivation and the percentage of neurons expres sing LAT appeared to increase, without a corresponding increase in vir ulence. These results strongly suggest that (i) the phenotypes of neur ovirulence and spontaneous reactivation are separable, (ii) the phenot ypes of corneal disease and spontaneous reactivation are separable, an d (iii) the decreased rate of spontaneous reactivation previously repo rted for d34.5 (G. C. Perng, R. L. Thompson, N. M. Sawtell, W. E. Tayl or, S. M. Slanina, H. Ghiasi, R. Kaiwar, A. B. Nesburn, and S. L. Wech sler, J. Virol. 69:3033-3041, 1995) is at least partially due to a red uced rate of establishing latency.