الفهرس 
VirologyOnly 14 pages are availabe for public view
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Abstract
Viruses which infect the central nervous system (CNS) can predominantly involve the spinal cord (myelitis), the brainstem (e.g. rhombencephalitis), the cerebellum (cerebellitis), or the cerebrum (encephalitis). Almost all acute viral infections of the CNS produce some degree of meningeal as well as parenchymal inflammation. The classic clinical features of all forms of viral encephalitis include fever, headache, an altered mental status, and focal neurological signs and symptoms. from a practical point of view, a clinician confronted by this set of symptoms must first distinguish encephalitis from non-infectious causes of brain dysfunction (encephalopathy). Having made this distinction, it is next necessary to distinguish cases in which brain injury is a direct consequence of viral infection from those cases in which it occurs as a consequence of a post-infectious immune-mediated process (e.g. acute disseminated encephalomyelitis). Finally, the goal in cases of encephalitis is to identify a specific etiologic agent, with particular emphasis on diseases that require acute treatment, such as herpes simplex encephalitis (HSE).
A virus gains access to the CNS generally by one of two routes: hematogenous or neuronal. Hematogenous spread is most common and is exemplified by arthropod-borne viral disease. Following an insect bite and local replication of virus at a skin site, transient viremia may ensue, with seeding of the reticuloendothelial system, particularly liver and spleen.Viral infections of the central nervous system (CNS), with a few exceptions, are difficult to diagnose. However, the advent of antiviral therapy has resulted in increased attention to the prompt and specific diagnosis and treatment of such infections of the CNS as herpes simplex encephalitis (HSE). In general, viral encephalitis can be subdivided into categories based on etiology and pathogenesis: 1) acute encephalitis, 2) post infectious encephalomyelitis, 3) slow viral infections of the CNS, and 4) chronic degenerative diseases of the CNS of presumed viral etiology.
HSE is the most common cause of acute sporadic (non-epidemic) focal encephalitis.
Encephalitis is an unusual manifestation of human viral infection. Thus, whereas many individuals develop symptomatic infection of the central nervous system (CNS). Viruses vary widely in their potential to produce significant CNS infection. For some viruses (e.g., mumps), CNS infection is a common but a relatively benign part of the syndrome. For others (e.g., Japanese encephalitis), neurological disease is the most prominent clinical feature of the systemic infection. A third group of viruses are those which commonly cause infection, but only rarely cause encephalitis (e.g., herpes simplex virus [HSV]). Lastly, there are viruses for which human infection inevitably and exclusively results in CNS disease (e.g., rabies). In addition to acute pathology, other viruses (e.g., measles) can cause syndromes of post-infectious encephalopathy
Diagnosis of viral infections of the CNS has been revolutionized by the advent of new technologies including the use of polymerase chain reaction (PCR) to amplify viral nucleic acid from cerebrospinal fluid (CSF).