Potential routes taken by VZV during its life cycle. Potential routes taken by VZV during its life cycle. Dorsal (sensory) and ventral (motor) roots carrying axons leave the spinal cord and fuse to form a mixed spinal nerve. A dorsal root ganglion (DRG) is present within the dorsal root. The DRG contains pseudounipolar sensory neurons (red) that extend a central process in the dorsal root to the posterior spinal cord and a peripheral process that reaches its targets of innervation via the spinal nerve. The skin is one such target, and sensory nerve fibers (red) ramify within the epidermis. Visceral sensory neurons also within the DRG send their peripheral process to the gut and terminate within the ganglia of the enteric nervous system (ENS) (submucosal and myenteric) or within other layers of the bowel wall. There is evidence that rare DRG neurons extend peripheral processes both to the skin and to the gut (indicated in the diagram). During varicella, retrograde transport from the skin can enable VZV to reach sensory neurons in the DRG and, from there, the neurons of the ENS (green arrows). Following the reactivation of VZV in a sensory DRG neuron, VZV can travel via anterograde transport in spinal nerve fibers to return to the skin and infect the epidermis in a restricted dermatomal distribution. Reactivation of VZV within neurons of the ENS affects the targets that these cells innervate and gives rise to local enteric disease, such as gastric ulceration (not illustrated) (see the text). Anne A. Gershon, and Michael D. Gershon Clin. Microbiol. Rev. 2013; doi:10.1128/CMR.00052-13