Corneal nerves contain intra-axonal HSV-1 after virus reactivation by epinephrine iontophoresis

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Abstract
Experimental ocular models of herpes simplex virus type 1 (HSV-1) reactivation have been used to monitor viral shedding in the tear film and the appearance of corneal epithelial lesions, but the temporal correlation between reactivation and the presence of viral particles in the corneal nerves has not been made. Two New Zealand white rabbits were inoculated with 20 μl of HSV-1 McKrae strain (5.0 ↣ 106 PFU/ml) in each eye. Beginning on postinfection day 82, ocular iontophoresis (0.8 mAmps for 8 min) of 0.01% epinephrine was done once a day for 3 consecutive days to induce reactivation. Ten limbal nerves from four corneas processed for transmission electron microscopy contained 883 unmyel inated and 40 myelinated axons. Seven nerves were positive for virus. Viral particles were found only in unmyel inated axons, and in low frequency (24/883). Virus was not found in Schwann cells, perineurium, or adjacent stroma nor were virus particles seen exiting axons. No enveloped virions were found. Axons from six nerves of four control corneas from rabbits with latent, but not reactivated, HSV-1 did not contain virus particles. Induction by corneal iontophoresis of epinephrine suggests that HSV-1 is translocated from the ganglion to the cornea through axonal transport mechanisms. For the first time, evidence of anterograde, intra-axonal transport of HSV-1 particles in response to epinephrine reactivation is demonstrated.