A wide variety of viruses cause encephalitis ( Table !)■ Viral pathogens produce damage or destruction of neurons, glia, and to a lesser extent cerebrovascular elements by establishing lytic infections of individual cells. After appropriating the host cell's metabolic machinery, viruses replicate rapidly and are released into the extracellular space through membrane rupture or the less catastrophic process of persistent budding from host cell membranes over variable periods of time. Viral antigens and the spilled contents of the host cell are potent chemoattractants which initiate an inflammatory response. Many viral pathogens establish latency in extra-axial neural tissues such as peripheral nerves (e.g. varicella zoster) or cranial ganglia (e.g. herpes simplex). In addition to lytic infection and establishment of extra-axial latency, some viruses are capable of producing a persistent infection within the central nervous system that leads to more gradual destruction of neurons or compromise of optimal cell function.
Table 1 Viral encephalitides
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