Fig. 4. The most common site of primary infection with herpes simplex virus type 1 (HSV-1) is the orofacial area served by the maxillary branch of the trigeminal ganglion. Infection here results in latent virus infection of neurons contained within the maxillary branch. At time of primary HSV-1 infection, or later at time of virus reactivation, virus can spread to the ophthalmic branch of the trigeminal ganglion, eventually causing HSV-1 infection in the ophthalmic division of the trigeminal ganglion without prior skin or mucous membrane HSV-1 infection in its distribution. (Liesegang TJ: Biology and molecular aspects of herpes simplex and varicella-zoster virus infections. Ophthalmology 99:781, 1992)