Etiology

Numerous viruses may cause viral meningitis. Some of these viruses are widespread, but many are endemic in specific geographic areas. Non-polio human enteroviruses are the most common cause of viral meningitis.[1][4][13] Herpes viruses cause a spectrum of central nervous system (CNS) disease, including meningitis, myelitis, and encephalitis. Herpes simplex virus (HSV)-1 is the most common cause of viral encephalitis in the Western world, whereas HSV-2 is more commonly associated with viral meningitis.[13] Varicella zoster virus is a relatively common cause of viral meningitis, which may occur during primary infection or with shingles but may occur without any rash.[13][14] Meningitis is a common manifestation of mumps, occurring in up to 10% of cases, although mumps is now uncommon in vaccinated populations.[15] Arboviruses cause neurologic infection in many parts of the world.[16] West Nile virus emerged in the US in 1999 and around 1 in 150 people infected develop neuroinvasive disease, such as meningitis or encephalitis.[12][17] Less common arboviruses in North America include Eastern and Western equine encephalitis viruses, La Crosse virus, and St. Louis encephalitis virus.[18][19] Viral meningitis may occur in 10% of symptomatic HIV seroconversion illnesses.[19] Viral meningitis is a rare manifestation of influenza. In up to 50% of cases, no etiological agent is identified.[13]

Pathophysiology

Enteroviruses are spread by the fecal-oral route.[3] The nonpolio enteroviruses and arboviruses initially replicate outside the CNS in tissues such as muscle, liver, and the respiratory or gastrointestinal tracts, and then reach the CNS by hematogenous spread. Viral penetration of the blood-brain barrier occurs by infection of either endothelial cells, migrating leukocytes, the choroid plexus epithelium, or lymphoid tissue.[16] It is unclear whether HSV infects the CNS as a result of hematogenous spread or by retrograde spread along peripheral nerves.[20] Once within the CNS, viruses spread through the subarachnoid space leading to meningitis, and may go on to infect neurons and glial cells leading to encephalitis or myelitis. The cellular immune response to viral infection of the CNS leads to the accumulation of lymphocytes within the cerebrospinal fluid (CSF) and the release of inflammatory cytokines such as interleukin (IL)-6 and TNF. The inflammatory response increases the permeability of the blood-brain barrier and this allows diffusion of circulating immunoglobulins into the CSF. The importance of the cell-mediated response in controlling infection is illustrated by the increased incidence and severity of infection with varicella zoster virus and cytomegalovirus (CMV) in patients with impaired T-cell responses.

Use of this content is subject to our disclaimer