Figure 3.7.

Events leading to the passage of pseudorabies virus across the junction between nerve cells on its centripetal intra-axonal transit to the brain. (1) Virions replicate in the nucleus of a peripheral nerve cell, acquiring an envelope as they bud from the inner lamella of the nuclear envelope. (2) Virions traverse the endoplasmic reticulum. (3) Virions are subsequently released into the cytoplasm after a fusion event between the virion envelope and endoplasmic reticulum membrane. (4) Virions acquire another envelope at the Golgi apparatus. (5) Virions are transported across the cytoplasm in vacuoles. (6) Virions enter the next neuron by fusion of the viral envelope and plasma membrane at a synaptic terminus. (7) Virions, now without their envelope, are carried centrally by retrograde axoplasmic flow, reaching the cell body and nucleus of the neuron, where further replication occurs. The process continues, eventually bringing the virus to the brain, where necrotizing encephalitis follows. (8) Some virions invade and replicate in the Schwann cells of the myelin sheaths surrounding neurons, thereby amplifying the amount of virus available to invade neurons.

[From J. P. Card, L. Rinaman, R. B. Lynn, B. H. Lee, R. P. Meade, R. R. Miselis, and L. W. Enquit. Pseudorabies virus infection of the rat central nervous system: ultrastructural characterization of virus replication, transport and pathogenesis. J. Neurosci.13, 2515–2539 (1993), with permission.]