Comparative studies on activation of latent herpes simplex virus in rabbits

Latent infection was established in 113 rabbits by inoculation of herpes simplex virus type 1 (HSV-1) strain Kupka into the right scarified cornea. In animals succumbed from 88-387 days post-infection (p.i.), HSV-1 was detected in the cultured right cornea (RC) fragments of 2 out 45 rabbits (4.4%), while the cultured right trigeminal ganglion (RTG) fragments yielded virus in 60 out 70 animals (85.7%). Spontaneous virus shedding occurred nearly in the half (35) of 74 animals followed for a mean of 211 days; providing that swabbing of both eyes was made 1-2 times weekly, the positive isolation rate was 1.3% (73 out total 5648 samples). The following treatments were used for provocation: cyclophosphamide (CPA) alone, mechanical trauma to cornea in association with local administration of either xylene or adrenalin, and a combination of both CPA administration and corneal irritation. In the course of these treatments continued for 4-8 days, virus was reisolated in 9 out 59 rabbits, the average positive isolation rate from RC being 6.9% (29 out 420 samples). HSV-specific antigens were searched for in about 56 000 semiserial sections prepared from noncultured as well as cultured samples of RC, both Gasserian ganglia and brainstem coming from 87 rabbits with established latency, of which 42 underwent provocation. By direct fluorescent antibody (FA) staining single neurons positive for structural HSV antigens were found in 14% of noncultured RTG samples from untreated rabbits as compared to 37% of such samples from animals subjected to provocation. In the course of above treatments, explanted RC fragments were positive in 17 out of 42 animals (40.4%) indicating a 9-fold increase in comparison to non-stimulated rabbits. The results confirm the absence of any virus, either infectious or covert, at the inoculation site in 95.6% of rabbits autopsied later than 12 weeks p.i. They also imply that a reversed transport of HSV occurred upon either spontaneous of artificial virus activations.