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). 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 subarachnoid space is located between the middle layer and the inner layer of the meninges, which cover the brain and spinal cord (see Biology of the Nervous System: Viewing the Brain). It contains the cerebrospinal fluid.

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 includes meningitis caused by drugs, disorders that are not infections, or other organisms (such as the bacteria that cause Lyme disease or syphilis).

Causes

The most common cause of viral meningitis is

• Enteroviruses, such as echovirus and coxsackievirus

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

Other common causes include

• Herpes simplex virus (HSV), usually type 2 (HSV-2)
• Mosquito-borne viruses (called arboviruses), such as West Nile virus, St. Louis encephalitis virus, and California encephalitis virus
• Lymphocytic choriomeningitis virus
• Human immunodeficiency virus (HIV)

HSV-2 causes genital herpes, a sexually transmitted disease that causes painful blisters in the genital area. This virus remains in the body in a nonactive (dormant) state, without causing symptoms. It reactivates periodically and causes symptoms. When HSV-2 causes meningitis, it usually does so when it first infects the body, not when it reactivates. Meningitis due to HSV-2 may occur before genital symptoms appear. Sometimes genital symptoms do not develop. Meningitis due to HSV-2 can recur (see Meningitis: Viruses).

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 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 and St. Louis virus)
• Spread through the air by inhaling the 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.

Symptoms

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.

Diagnosis

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—see Symptoms and Diagnosis of Brain, Spinal Cord, and Nerve Disorders: Spinal Tap) is done to obtain a sample of cerebrospinal fluid, which 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 and herpesviruses. Doctors also test cerebrospinal fluid for the presence of antibodies to certain viruses. For example, high levels of antibodies to West Nile virus indicate infection with that virus.

Doctors sometimes also withdraw a sample of blood for culture, examination, and, 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.

Treatment

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 (see Meningitis: Acute Bacterial Meningitis). They are also given acyclovirSome Trade Names
ZOVIRAX
(an antiviral drug) in case the infection is due to HSV.

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, called highly active antiretroviral therapy (HAART). People must take these drugs for the rest of their life.

If the cause is HSV, acyclovirSome Trade Names
ZOVIRAX
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, acetaminophenSome Trade Names
TYLENOL
, taken by mouth or suppository (inserted into the rectum), can reduce fever. Pain relievers (analgesics), taken as needed, can help control headache.

Prognosis

Most people 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.

Last full review/revision February 2013 by John E. Greenlee, MD