Histopathologic characteristics of two forms of experimental herpes simplex virus retinitis

Herpes simplex virus type 1 (HSV-1) inoculated intracamerally into one anterior chamber of a BALB/c mouse produces retinitis in the uninoculated contralateral eye within 7 to 10 days while the retina of the inoculated eye is spared. In sharp contrast, animals receiving HSV type 2 (HSV-2) by the anterior chamber route develop a dramatic retinitis in the inoculated eye by day 7 postinoculation while the retina of the contralateral eye remains uninvolved. Histopathologic examination of retinal destruction in the HSV-2-infected ipsilateral eye revealed features which were distinct from those observed in the contralateral eye of HSV-1-infected animals. Whereas HSV-1 produced a rapid, explosive, retinitis which led to destruction of all cell layers of the contralateral retina, HSV-2 induced a retinitis in the ipsilateral eye that was more gradual in onset. Ipsilateral HSV-2 retinitis was characterized initially by disruption of the ganglion and inner nuclear layers which progressed by day 10 to 14 to complete replacement of the retina by a fibrocellular scar. These changes were dominated by a vigorous mononuclear cell infiltrate, a feature not observed in the HSV-1-infected contralateral retinitis. These results suggest that experimental retinitides produced by HSV-1 and HSV-2 are of diverse pathogenesis.