Skip to main content


Medically reviewed by Last updated on Mar 16, 2023.


Encephalitis (en-sef-uh-LIE-tis) is inflammation of the brain. There are several causes, including viral infection, autoimmune inflammation, bacterial infection, insect bites and others. When inflammation is caused by an infection in the brain, it's known as infectious encephalitis. And when it's caused by your own immune system attacking the brain, it's known as autoimmune encephalitis. Sometimes there is no known cause.

In some cases, encephalitis can be life-threatening. Prompt diagnosis and treatment are important because it's difficult to predict how encephalitis will affect each individual.


Encephalitis may cause many different symptoms including confusion, personality changes, seizures or problems with movement. Encephalitis also may cause changes in sight or hearing.

Most people with infectious encephalitis have flu-like symptoms, such as:

Typically, these are followed by more-severe symptoms over a period of hours to days, such as:

In infants and young children, signs and symptoms also might include:

In cases of autoimmune encephalitis, symptoms may develop more slowly over several weeks. Flu-like symptoms are less common, but can sometimes happen weeks before more-severe symptoms start. Symptoms are different for everyone, but it's common for people to have a combination of symptoms including:

When to see a doctor

Get immediate care if you are experiencing any of the more-severe symptoms associated with encephalitis. A severe headache, fever and change in consciousness require urgent care.

Infants and young children with any signs or symptoms of encephalitis should receive urgent care.

Bulging fontanel

One of the major signs of encephalitis in infants is bulging of the soft spots (fontanels) of the baby's skull. Pictured here is the anterior fontanel. Other fontanels are found on the sides and back of an infant's head.


In approximately half of patients, the exact cause of encephalitis is not known.

In those for whom a cause is identified, there are two main types of encephalitis:

Common viral causes

The viruses that can cause encephalitis include:

West Nile virus transmission cycle

When a mosquito bites an infected bird, the virus enters the mosquito's bloodstream and eventually moves into its salivary glands. When an infected mosquito bites an animal or a human (host), the virus is passed into the host's bloodstream, where it may cause serious illness.

Risk factors

Anyone can develop encephalitis. Factors that may increase the risk include:


The complications of encephalitis vary, depending on factors such as:

People with relatively mild illness usually recover within a few weeks with no long-term complications.

Complications of severe illness

Inflammation can injure the brain, possibly resulting in a coma or death.

Other complications may last for months or be permanent. These complications can vary widely in severity and can include:


The best way to prevent viral encephalitis is to take precautions to avoid exposure to viruses that can cause the disease. Try to:

Protection against mosquitoes and ticks

To minimize your exposure to mosquitoes and ticks:

Protection for young children

Insect repellents aren't recommended for use on infants younger than 2 months of age. Instead, cover an infant carrier or stroller with mosquito netting.

For older infants and children, repellents with 10% to 30% DEET are considered safe. Products containing both DEET and sunscreen aren't recommended for children because reapplication — which might be necessary for the sunscreen component — will expose the child to too much DEET.

Tips for using mosquito repellent with children include:


Your health care provider will start with a thorough physical examination and medical history.

Your provider might then recommend:


Treatment for mild encephalitis usually consists of:

Antiviral medicines

Encephalitis caused by certain viruses usually requires antiviral treatment.

Antiviral medicines commonly used to treat encephalitis include:

Some viruses, such as insect-borne viruses, don't respond to these treatments. But because the specific virus may not be identified immediately or at all, health care providers often recommend immediate treatment with acyclovir. Acyclovir can be effective against HSV, which can result in significant complications when not treated promptly.

Antiviral medicines are generally well tolerated. Rarely, side effects can include kidney damage.

Autoimmune encephalitis

If the tests show an autoimmune cause of encephalitis, then medicines that target your immune system, known as immunomodulatory medicines, or other treatments may be started. These may include:

Some people with autoimmune encephalitis need long-term treatment with immunosuppressive medicines. These may include azathioprine (Imuran, Azasan), mycophenolate mofetil (CellCept), rituximab (Rituxan) or tocilizumab (Actemra).

Autoimmune encephalitis caused by tumors may require treatment of those tumors. This may include surgery, radiation, chemotherapy or a combination of treatments.

Supportive care

People who are hospitalized with severe encephalitis might need:

Follow-up therapy

If you experience complications of encephalitis, you might need additional therapy, such as:

Preparing for an appointment

Serious illness associated with encephalitis is usually severe and relatively sudden, so seek emergency care. The emergency care team will likely include specialists in infectious diseases, the brain and nervous system (neurologist).

Questions from your doctor

You may need to answer these questions, or answer them on behalf of your child or another person with severe illness:

© 1998-2024 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. Terms of use.

Learn more about Encephalitis

Treatment options

Symptoms and treatments