Merck Manual

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Viral Meningitis


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 is inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid space) when it is caused by viruses.

  • Viral meningitis usually begins with symptoms of a viral infection such as fever, a general feeling of illness, headache, and muscle aches.

  • Later, people develop a headache and a stiff neck that makes lowering the chin to the chest difficult or impossible.

  • Doctors suspect viral meningitis based on symptoms and do a spinal tap (lumbar puncture) to confirm the diagnosis.

  • If people appear very ill, they are treated for bacterial meningitis until that diagnosis is ruled out.

  • If the cause is human immunodeficiency virus (HIV) or a herpesvirus, drugs effective against those viruses are used.

  • For other viruses, no effective drugs are available, but most people recover on their own within weeks.

The brain and spinal cord are covered by three layers of tissue called meninges. The subarachnoid space is located between the middle layer and the inner layer of the meninges, which cover the brain and spinal cord. It contains the cerebrospinal fluid, which flows through the meninges, fills the spaces within the brain, and helps cushion the brain and spinal cord.

Viral meningitis is the most common cause of aseptic meningitis. Aseptic meningitis refers to meningitis that is caused by anything other than the bacteria that typically cause meningitis. Thus, aseptic meningitis can include meningitis caused by drugs, disorders that are not infections, or other organisms (such as the bacteria that cause Lyme disease or syphilis).

Tissues Covering the Brain

Within the skull, the brain is covered by three layers of tissue called the meninges:

  • Dura mater (outer layer)

  • Arachnoid mater (middle layer)

  • Pia mater (inner layer)

Between the arachnoid membrane and pia mater is the subarachnoid space. This space contains cerebrospinal fluid, which flows through the meninges, fills the spaces within the brain, and helps cushion the brain and spinal cord.

Tissues Covering the Brain


The most common cause of viral meningitis is

Enteroviruses tend to reside in the digestive tract. Infections are very contagious.

Other common causes include

HSV-2 causes genital herpes, a sexually transmitted disease that causes painful blisters in the genital area. HSV-2 can also cause symptoms of meningitis. HSV-2 meningitis usually occurs when the virus first infects the body. Genital and meningitis symptoms can occur at the same time. Symptoms of meningitis may appear before the genital symptoms, and some people have meningitis but do not have any genital symptoms. After symptoms disappear, HSV-2 remains in the body in a nonactive (dormant) state. That is, it does not cause symptoms. However, it can become active again (reactivate) periodically and cause symptoms. Thus, meningitis due to HSV-2 can recur.

The varicella-zoster virus causes chickenpox. Like HSV-2, the varicella-zoster virus remains in the body in a nonactive state. The virus may never cause symptoms again, or it may reactivate many years later. When it reactivates, it causes shingles (herpes zoster) and may cause meningitis. Unlike HSV infections, which can recur many times, shingles usually occurs only once in a person's lifetime. However, people with a weakened immune system (such as people with HIV infection) may have shingles more than once.

Zika virus and Chikungunya virus sometimes cause meningitis. Both viruses were once present in only a few parts of the world but now have spread.

Transmission of viral meningitis

Viral meningitis can be spread in several ways, depending on the virus:

  • Spread through the bloodstream from an infection in another part of the body (the most common way)

  • Contact with contaminated stool, which may occur when infected people do not wash their hands after a bowel movement or when they swim in a public swimming pool (for enteroviruses)

  • Sexual intercourse or other genital contact with an infected person (for HSV-2 and HIV)

  • A bite of an insect, such as a mosquito (for West Nile virus, St. Louis virus, Zika virus, or Chikungunya virus)

  • Spread through the air by inhaling the virus (for varicella-zoster virus)

  • Contact with dust or food contaminated by the urine or stool of infected mice or pet hamsters (for lymphocytic choriomeningitis virus)

  • Use of infected needles to inject drugs (for HIV)

Because of the way they are spread, some viruses cause meningitis only during certain seasons.


Viral meningitis usually begins with symptoms of a viral infection, such as fever, a general feeling of illness (malaise), cough, muscle aches, vomiting, loss of appetite, and headache. However, occasionally, people have no symptoms at first.

Later, people have symptoms that suggest meningitis. That is, they typically have fever, headache, and a stiff neck. Trying to lower the chin to the chest causes pain and may be impossible. Moving the head in other directions is not as difficult.

Symptoms may resemble those of bacterial meningitis but are usually less severe and develop and progress more slowly.


  • Spinal tap and analysis of cerebrospinal fluid

  • Sometimes culture and testing of blood, other body fluids, or stool

Doctors suspect meningitis when people have a headache, fever, and stiff neck. They then try to determine whether meningitis is present and whether it is caused by bacteria (requiring immediate treatment) or a virus. Viral meningitis is more likely when the symptoms are less severe.

A spinal tap (lumbar puncture) is done to obtain a sample of cerebrospinal fluid. However, if doctors suspect that pressure within the skull is increased, computed tomography (CT) or magnetic resonance imaging (MRI) may be done first to check for causes of the increased pressure (such as a tumor or another mass in the brain). Doing a spinal tap when pressure within the skull is increased may cause a life-threatening disorder called brain herniation. After pressure within the skull is lowered or if no mass is detected, the spinal tap is done.

The sample of cerebrospinal fluid is sent to a laboratory to be examined and analyzed. Sugar and protein levels and the number and type of white blood cells in the fluid are determined. The fluid is cultured to check for bacteria and thus rule out or confirm bacterial meningitis. The fluid is not usually cultured for viruses because doing so is technically difficult.

The polymerase chain reaction (PCR) technique, which produces many copies of a gene, is used to identify enteroviruses, herpesviruses (such as HSV and varicella-zoster), and some other viruses. Doctors also test cerebrospinal fluid for the presence of antibodies to certain viruses. For example, detecting antibodies to West Nile virus in cerebrospinal fluid indicates infection with that virus.

Doctors sometimes also take a sample of blood, nasal or throat secretions, or stool for culture, examination, and/or, if available, PCR testing. HIV can be diagnosed based on the results of antibody tests and PCR. Levels of antibodies to other viruses are measured and sometimes remeasured a few weeks later. An increase in the level of antibodies to a particular virus indicates that the virus caused a recent infection and so probably was the cause of recent meningitis.


  • Acyclovir (an antiviral drug) for HSV or varicella-zoster infection

  • Antiretroviral drugs for HIV infection

  • Treatment of symptoms

If people appear very ill, doctors start treatment right away without waiting for test results to identify the cause. These people are given antibiotics until doctors are sure that they do not have bacterial meningitis, which, if untreated, can rapidly cause permanent brain or nerve damage or death. They are also given acyclovir (an antiviral drug) in case the meningitis is due to herpes simplex virus (HSV) or varicella-zoster infection.

After the cause is identified, doctors change drugs as needed.

HIV infection is treated with antiretroviral drugs. These drugs prevent HIV (a retrovirus) from reproducing and multiplying inside human cells. Almost always, people need to take a combination of several antiretroviral drugs. People must take these drugs for the rest of their life.

If the cause is HSV or varicella-zoster infection, acyclovir is continued.

For most of the other viruses that commonly cause meningitis, there are no effective drugs. However, if people have a normal immune system, they almost always recover from these infections on their own.

Symptoms are also treated. For example, acetaminophen, taken by mouth or suppository (inserted into the rectum), can reduce fever. Pain relievers (analgesics), taken as needed, can help control headache.


Most people who have viral meningitis recover within a few weeks. Occasionally, recovery can take months, as sometimes occurs when meningitis is caused by West Nile virus or lymphocytic choriomeningitis virus.

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