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Viral Meningitis

By

John E. Greenlee

, MD, University of Utah School of Medicine

Last full review/revision Aug 2019| Content last modified Aug 2019
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Viral meningitis tends to be less severe than acute bacterial meningitis. Findings include headache, fever, and nuchal rigidity. Diagnosis is by cerebrospinal fluid (CSF) analysis. Treatment is with supportive measures, acyclovir for suspected herpes simplex, and antiretroviral drugs for suspected HIV infection.

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

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).

Table
icon

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

Varicella-zoster virus

Inhalation of respiratory droplets from or by contact with an infected person

None

Western equine virus†

Venezuelan equine virus†

Mosquito

Summer to early autumn

West Nile virus

St. Louis virus

Mosquito

Summer to early autumn

California encephalitis virus

La Crosse virus

Mosquito

Summer to early autumn

Colorado tick fever virus (unusual)

Ticks

Late spring to early summer

Lymphocytic choriomeningitis virus

Airborne‡

Autumn to winter

HIV-1

HIV-2

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.

Symptoms and Signs

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

  • 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 newly available 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

  • If patients appear seriously ill, treat them for acute bacterial meningitis until it is ruled out, even if the cause is suspected to be viral.

Treatment

  • Supportive measures

  • Acyclovir (for suspected herpes simplex or herpes zoster) and antiretroviral drugs (for HIV infection)

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.

Acyclovir is efficacious in treating herpes simplex meningitis and can be used to treat herpes zoster meningitis. If either of these viruses is suspected or if herpes simplex encephalitis is at all suspected, most clinicians begin empiric treatment with acyclovir and, if PCR is negative for these viruses, then stop the drug.

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.

  • Treatment is mainly supportive; patients with herpes simplex or herpes zoster meningitis may be treated with acyclovir.

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