Quantitation of herpes simplex virus type 1 DNA and latency-associated transcripts in rabbit trigeminal ganglia demonstrates a stable reservoir of viral nucleic acids during latency

In this investigation we determined the dynamics of herpes simplex virus type 1 (HSV-1) DNA and latency associated transcripts (LAT) in the latently infected rabbit trigeminal ganglion. Rabbit eyes were infected with either the McKrae strain or the 17Syn(+) strain of HSV-1. Rabbits were sacrificed between 5 and 360 days after infection and their trigeminal ganglia were analyzed for the number of HSV DNA genomes and the number of neuronal cells expressing LAT. There was no statistically significant change in the number of HSV genomes or the number of neuronal cells expressing LAT in these ganglia between 20 and 360 days after infection. For both strains, the amount of HSV DNA averaged 16.8 genomes per 100 cells, and 9.2% of the neurons expressed LAT. There were 17 to 34 HSV genomes per LAT-expressing neuronal cell, The number of LAT-expressing neurons did not change over the 360 days. Spontaneous reactivation (HSV-1 recovery in tear film) and recurrence (HSV-l-specific epithelial lesions) occurred during the period of this study; however,these events did not alter the quantity of HSV-1 DNA or the number of LAT-expressing cells. These results suggest that after the latent infection is established, the viral DNA in the ganglia does not replicate to any measurable extent over long periods of latency, since no significant change in the number of HSV genomes occurs. The results also suggest that only a very small number of latently infected neuronal cells are needed to produce infectious HSV-1 during reactivation.