Glycoprotein D-negative pseudorabies virus can spread transneuronally via direct neuron-to-neuron transmission in its natural host, the pig, but not after additional inactivation of gE or gI

Abstract

Envelope glycoprotein D (gD) is essential for entry of pseudorabies virus (PRV) into cells but is not required for the subsequent steps in virus replication. Phenotypically complemented gD mutants can infect cells and can spread, both in vitro and in mice, by direct cell-to-cell transmission. Progeny virions released by infected cellsare noninfectious because they lack gD. The aim of this study was to determine the role of gD in the neuropathogenicity of PRV in its natural host, the pig. We investigated whether gD-negative PRV can spread transneuronally via synaptically linked neurons of the olfactory and trigeminal routes. High doses of a phenotypically complemented gD mutant and gD mutants that are unable to express either gI or gI plus gE were inoculated intranasally in 3-to 5-week-old pigs. Compared with the wild-type virus, the virulence of the gD mutant was reduced. However, pigs inoculated with the gD mutant still developed fever and respiratory signs. Additional inactivation of either gI or gI plus gE further decreased virulence for pigs. Immunohistochemical examination of infected pigs showed that a PRV gD mutant could replicate and spread transneuronally into the central nervous system (CNS). Compared with the wild-type virus, the gD mutant had infected fewer neurons of the CNS on day 2. Nevertheless, on day 3, the gD-negative PRV had infected more neurons and viral antigens were present in second-and third-order neurons in the olfactory bulb, brain stem, and medulla oblongata. In contrast, gD mutants which are unable to express either gI or gI plus gE infected a limited number of first-order neurons in the olfactory epithelium and in the trigeminal ganglion and did not spread transneuronally or infect the CNS. Thus, transsynaptic spread of PRV in pigs can occur independently of gD. Possible mechanisms of transsynaptic transport of PRV are discussed.

Severe Acute Respiratory Syndrome Coronavirus Infection of Mice Transgenic for the Human Angiotensin-Converting Enzyme 2 Virus Receptor

“…It has been well established that the spread of respiratory viruses to the brain could be mediated either directly through synaptically linked neurons of the olfactory and trigeminal systems, as described in the animal models for Venezuelan equine encephalitis virus, pseudorabies virus, and avian influenza virus A (H5N1) infection (8,14,25,33), or through the hematogenous route, via the damaged blood-brain barrier. Al-though the exact route or routes of SARS-CoV dissemination to the CNS remain to be determined, the revelation of lowlevel viremia in infected (i.n.)…”

Sorting and Transport of Alpha Herpesviruses in Axons

“…For PRV, gD is required for particles to infect cells: gD null mutants produce virions that are not infectious (54,55). Surprisingly, PRV gD null mutants can spread from cell to cell in cultured cells as well as in the nervous system of animals (56–58). No infectious virus particles are produced in these animal infections.…”

Glycoproteins gM and gN of Pseudorabies Virus Are Dispensable for Viral Penetration and Propagation in the Nervous Systems of Adult Mice

“…In the absence of gB or gH, infection did not spread, indicating that both glycoproteins are essential for the penetration of neurons from the respiratory epithelium and for local or transneuronal transfer between neurons (1, 4). In contrast, after primary infection by complemented virions, the presence of gD was not required for virus spread from the respiratory epithelium to neurons, between neurons by local and transneuronal transfer, and between neurons and glial cells (1,21). This mimics the situation found in cell cultures (23,24).…”

“…Interestingly, glycoproteins gE and gI are dispensable for viral replication in cell cultures but are specifically required for transneuronal transfer of PrV between infected first-order neurons and several categories of connected neurons. For instance, after intranasal inoculation, a gE Ϫ PrV mutant is not transmitted to second-order neurons of the trigeminal, sympathetic, or parasympathetic route (3,11,15,17,21,22). In rats, after inoculation into the posterior chamber of the eye, infection of the retina occurs normally but propagation of the mutant is restricted to a subset of neurons connected to ganglionic cells, e.g., those involved in circadian timing (6,9,10,16,18,20,(26)(27)(28).…”