(See also Overview of Meningitis.)
Viral meningitis is sometimes used synonymously with aseptic meningitis. However, aseptic meningitis usually refers to acute meningitis caused by anything other than the bacteria that typically cause acute bacterial meningitis. Thus, aseptic meningitis can be caused by viruses, noninfectious conditions (eg, drugs, disorders), fungi, or, occasionally, other organisms (eg, Borrelia burgdorferi in Lyme disease, Treponema pallidum in syphilis).
Unlike bacterial meningitis, viral meningitis usually spares the brain parenchyma. (Parenchyma is affected in viral encephalitis or meningoencephalitis.)
Causes of Viral Meningitis
Viral meningitis usually results from hematogenous spread, but meningitis due to herpes simplex virus type 2 (HSV-2) or varicella-zoster virus can also result from reactivation of latent infection. Recurrent attacks of viral meningitis in women are usually due to HSV-2.
The most common cause of viral meningitis is
Enteroviruses
For many viruses that cause meningitis (unlike the bacteria that cause acute bacterial meningitis), incidence is seasonal (see table Common Causes of Viral Meningitis).
Common Causes of Viral Meningitis
Virus | Mechanism of Transmission | Seasonal Incidence |
|---|---|---|
Enteroviruses (eg, coxsackieviruses, echoviruses) | Fecal-oral spread (eg, via contaminated food, in swimming pools) | Summer to early autumn Sometimes sporadic cases throughout year |
Herpes simplex, usually virus type 2* | Close or sexual contact with a person actively shedding the virus | None |
Inhalation of respiratory droplets from or by contact with an infected person | None | |
Eastern equine encephalitis virus† Venezuelan equine virus† | Mosquito | Summer to early autumn |
Flaviviruses:
| Mosquito | Summer to early autumn |
Orthobunyaviruses:
| Mosquito | Summer to early autumn |
Powassan virus | Ticks | Late spring to early summer; mid autumn |
Colorado tick fever virus (unusual) | Ticks | Late spring to early summer |
Airborne‡ | Autumn to winter | |
Contact with body fluids of an infected person | None§ | |
* Herpes simplex type 2 meningitis may occur as an isolated instance or may recur. | ||
† Western equine and Venezuelan equine viruses have been associated with meningitis, but no cases have been reported in the US in recent years. | ||
‡ Lymphocytic choriomeningitis virus is associated with exposure to infected wild mice (the natural host for this virus) and is most common during autumn or winter when mice tend to move indoors. Infection may also occur year-round when the cause is exposure to infected pet hamsters. | ||
§ Meningitis due to HIV usually begins early in the course of systemic infection—when seroconversion occurs. | ||
Zika virus and Chikungunya virus are uncommon causes of meningitis, but these viruses should be considered in people who have traveled to endemic areas if they develop symptoms that suggest meningitis.
Occasionally, meningitis, usually accompanied by encephalitis, develops in patients with COVID-19. Rarely, meningitis in COVID-19 patients is due to coinfection by another virus (eg, varicella-zoster virus).
Symptoms and Signs of Viral Meningitis
Viral meningitis, like acute bacterial meningitis, usually begins with symptoms that suggest viral infection (eg, fever, myalgias, gastrointestinal or respiratory symptoms), followed by symptoms and signs of meningitis (headache, fever, nuchal rigidity). Manifestations tend to resemble those of bacterial meningitis but are usually less severe (eg, nuchal rigidity may be less pronounced). However, findings are sometimes severe enough to suggest acute bacterial meningitis. Because brain parenchyma is spared, delirium, confusion, seizures, and focal or global neurologic deficits are absent.
Diagnosis of Viral Meningitis
Cerebrospinal fluid (CSF) analysis (cell count, protein, glucose)
Polymerase chain reaction (PCR) of CSF and sometimes IgM
Sometimes PCR and/or culture of blood, a throat swab, nasopharyngeal secretions, or stool
Diagnosis of viral meningitis is based on analysis of CSF obtained by lumbar puncture (preceded by neuroimaging if increased intracranial pressure or a mass is suspected). Typically, protein is slightly increased but less than that in acute bacterial meningitis (eg, < 150 mg/dL); however, the protein level can be very high in West Nile virus meningitis. Glucose is usually normal or only slightly lower than normal. Other findings include pleocytosis with a lymphocytic predominance. Nonetheless, no combination of findings in CSF cells, protein, and glucose can rule out bacterial meningitis. Bacterial meningitis is eventually ruled out if no bacteria grow in CSF cultures. However, if a patient with bacterial meningitis took antibiotics (ie, was partially treated) before blood cultures and lumbar puncture, CSF findings may resemble those of viral meningitis; thus, if patients were partially treated, empirical antibiotic treatment for bacterial meningitis may be warranted even though viral meningitis is suspected.
CSF viral culture is insensitive and not routinely done. PCR can be used to detect some viruses in CSF (enteroviruses and herpes simplex, herpes zoster, West Nile viruses); a multiplex film-array PCR panel can be used to rapidly screen for multiple bacteria and viruses. Measurement of IgM in CSF is more sensitive than PCR in diagnosing suspected West Nile virus or other arboviruses.
Patients with HSV-2 meningitis may have enlarged mononuclear cells (Mollaret cells) in the CSF. HSV-2 meningitis often recurs (called Mollaret meningitis).
Viral serologic tests, PCR, or culture of samples taken from other areas (eg, blood, a throat swab, nasopharyngeal secretions, stool) may help identify the causative virus.
Pearls & Pitfalls
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Treatment of Viral Meningitis
Supportive measures
If patients appear seriously ill and if acute bacterial seems possible (even if viral meningitis is suspected), appropriate antibiotics and corticosteroids are started immediately (without waiting for test results) and continued until bacterial meningitis is ruled out (ie, no bacteria grow in CSF cultures).
Viral meningitis usually resolves spontaneously over weeks or, occasionally (eg, in West Nile virus meningitis or lymphocytic choriomeningitis), months. Treatment is mainly supportive.
herpes simplex meningitis and can be used to treat herpes zoster meningitis
Pleconaril is only modestly efficacious for meningitis due to enteroviruses and is not available for routine clinical use.
Patients with HIV meningitis are treated with antiretroviral drugs.
Key Points
Viral meningitis begins with symptoms typical of a viral illness, followed by headache, fever, and nuchal rigidity, but is rarely as severe as acute bacterial meningitis.
Enteroviruses are the most common cause, usually causing infection during summer or early autumn.
CSF findings (usually lymphocytic pleocytosis, near normal glucose, and slightly increased protein) cannot exclude acute bacterial meningitis.
Treat patients for acute bacterial meningitis until that diagnosis is ruled out.
