ABSTRACT
Viral infections of the nervous system often result in devastating consequences and can range from a fulminant encephalitis or myelitis to a subacute or chronic illness. Incubation periods are usually short but in some cases it can range from months to years. The mechanisms by which they enter the brain or spinal cord and cause neuroglial injury are very complex. Most spread by cell-to-cell contact within the brain including a trans-synaptic spread. Brain can also serve as a reservoir for some viruses. Most viruses have cell type and regional preferences in the brain and thus can present with distinct clinical syndromes. Immune responses to viral pathogens in the brain are unique. They manifest as strong innate immune responses, but the presence of adaptive immune response in the brain or spinal fluid may signal the presence of an infectious process. It is also clear that the cellular dysfunction exceeds beyond the infected cells due to the release of toxic proteins, cytokines, chemokines, and induction of oxidative stress by the infected cells or the activated glial cells. These infections can also trigger an autoimmune encephalitis adding to the complexity of patient management.
