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BOX 2.10 TERMINOLOGY Infection of the nervous system: definitions and distinctions

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 A neuroinvasive virus can enter the central nervous system (spinal cord and brain) after infection of a peripheral site.

 A neurotropic virus can infect neurons; infection may occur by neural or hematogenous spread from a peripheral site.

 A neurovirulent virus can cause disease of nervous tissue, manifested by neurological symptoms and often death.

Examples:

 Herpes simplex virus type 1 exhibits low neuroinvasiveness but high neuroviru lence. It always enters the peripheral nervous system but rarely gains access to the central nervous system. When it does, the consequences are severe, and can be fatal. Mumps virus exhibits high neuroinvasiveness but low neurovirulence. Most infections lead to invasion of the central nervous system, but neurological disease is mild. Rabies virus is highly neuroinvasive, with high neurovirulence. It readily infects the peripheral nervous system and spreads to the central nervous system with 100% lethality, unless postinfection vaccination is given.


Primary mouse hippocampal neurons expressing a measles virus receptor, CD46, and infected with measles virus for 48 h. Virus-infected cells are stained brown. Black arrow: neuronal axon; white arrow: neuronal dendrites. Original magnification = ×200. Photo courtesy of the Rall laboratory.

Figure 2.16 Possible pathways for the spread of infection in nerves. Virus particles may enter sensory or motor neuron endings. They may be transported within axons, in which case viruses taken up at sensory endings reach dorsal root ganglion cells. Those taken up at motor endings reach motor neurons. Viruses may also travel in the endoneural space, perineural lymphatics, or infected Schwann cells. Directional transport of virus particles inside the sensory neuron is defined as anterograde [movement from the (–) to the (+) ends of microtubules] or retrograde (vice versa).

Principles of Virology, Volume 2

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