(See also Overview of Meningitis Overview of Meningitis Meningitis is inflammation of the meninges and subarachnoid space. It may result from infections, other disorders, or reactions to drugs. Severity and acuity vary. Findings typically include... read more .)
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 Acute Bacterial Meningitis Acute bacterial meningitis is rapidly progressive bacterial infection of the meninges and subarachnoid space. Findings typically include headache, fever, and nuchal rigidity. Diagnosis is by... read more ), incidence is seasonal (see table ).
Zika virus Zika Virus (ZV) Infections The Zika virus is a mosquito-borne flavivirus that is antigenically and structurally similar to the viruses that cause dengue, yellow fever, and West Nile virus. Zika virus infection is typically... read more and Chikungunya virus Chikungunya disease Arbovirus (arthropod-borne virus) applies to any virus that is transmitted to humans and/or other vertebrates by certain species of blood-feeding arthropods, chiefly insects (flies and mosquitoes)... read more 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 Encephalitis Encephalitis is inflammation of the parenchyma of the brain, resulting from direct viral invasion or occurring as a postinfectious immunologic complication caused by a hypersensitivity reaction... read more , develops in patients with COVID-19 COVID-19 COVID-19 is an acute, sometimes severe, respiratory illness caused by the novel coronavirus SARS-CoV-2. Prevention is by vaccination and infection control precautions (eg, face masks, handwashing... read more . 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 Symptoms and Signs Acute bacterial meningitis is rapidly progressive bacterial infection of the meninges and subarachnoid space. Findings typically include headache, fever, and nuchal rigidity. Diagnosis is by... read more , 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 Lumbar puncture Acute bacterial meningitis is rapidly progressive bacterial infection of the meninges and subarachnoid space. Findings typically include headache, fever, and nuchal rigidity. Diagnosis is by... read more (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 West Nile Virus West Nile virus is a flavivirus that is now the primary cause of arbovirus encephalitis in the US. Most patients have mild or no symptoms. About 1 out of 150 patients develop a severe infection... read more . 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 Overview of Enterovirus Infections Enteroviruses, along with rhinoviruses (see Common Cold) and human parechoviruses, are a genus of picornaviruses (pico, or small, RNA viruses). All enteroviruses are antigenically heterogeneous... read more and herpes simplex Herpes Simplex Virus (HSV) Infections Herpes simplex viruses (human herpesviruses types 1 and 2) commonly cause recurrent infection affecting the skin, mouth, lips, eyes, and genitals. Common severe infections include encephalitis... read more 
, herpes zoster Herpes Zoster Herpes zoster is infection that results when varicella-zoster virus reactivates from its latent state in a posterior dorsal root ganglion. Symptoms usually begin with pain along the affected... read more 
, West Nile West Nile Virus West Nile virus is a flavivirus that is now the primary cause of arbovirus encephalitis in the US. Most patients have mild or no symptoms. About 1 out of 150 patients develop a severe infection... read more 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 Overview of Arbovirus, Arenavirus, and Filovirus Infections Arbovirus (arthropod-borne virus) applies to any virus that is transmitted to humans and/or other vertebrates by certain species of blood-feeding arthropods, chiefly insects (flies and mosquitoes)... read more .
Patients with HSV-2 meningitis may have enlarged mononuclear cells (Mollaret cells) in the CSF. HSV-2 meningitis often recurs (called Mollaret meningitis) Recurrent viral meningitis Recurrent meningitis is usually caused by bacteria, viruses, or noninfectious conditions. (See also Overview of Meningitis.) Recurrent viral meningitis is most often due to Herpes simplex virus... read more .
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.
Treatment of Viral Meningitis
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 West Nile Virus West Nile virus is a flavivirus that is now the primary cause of arbovirus encephalitis in the US. Most patients have mild or no symptoms. About 1 out of 150 patients develop a severe infection... read more or lymphocytic choriomeningitis Lymphocytic Choriomeningitis Lymphocytic choriomeningitis is caused by an arenavirus. It usually causes a flu-like illness or aseptic meningitis, sometimes with rash, arthritis, orchitis, parotitis, or encephalitis. Diagnosis... read more ), months. Treatment is mainly supportive.
Acyclovir is efficacious in treating herpes simplex meningitis Herpes Simplex Virus (HSV) Infections Herpes simplex viruses (human herpesviruses types 1 and 2) commonly cause recurrent infection affecting the skin, mouth, lips, eyes, and genitals. Common severe infections include encephalitis... read more and can be used to treat herpes zoster meningitis Herpes Zoster Herpes zoster is infection that results when varicella-zoster virus reactivates from its latent state in a posterior dorsal root ganglion. Symptoms usually begin with pain along the affected... read more . 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 Overview of Enterovirus Infections Enteroviruses, along with rhinoviruses (see Common Cold) and human parechoviruses, are a genus of picornaviruses (pico, or small, RNA viruses). All enteroviruses are antigenically heterogeneous... read more and is not available for routine clinical use.
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.
