Encephalitis is brain inflammation (swelling). Causes include viral infections, infections from insect bites or an autoimmune reaction that affects your brain. It can be life-threatening or cause long-term complications. Treatment varies, but most people require hospitalization so they can receive intensive treatment, including life support.


What is encephalitis?

Encephalitis is a rare, serious condition that causes inflammation in your brain so that it swells. It can occur as a result of an infection or an autoimmune process. Encephalitis can be life-threatening, regardless of the cause, and can cause long-term complications and medical issues. Treatment varies depending on the cause, but most people with encephalitis require hospitalization so they can receive intensive treatment, including life support measures.

Types of encephalitis

Condition types include infective encephalitis and autoimmune encephalitis. Infective encephalitis includes:

  • Viral encephalitis: This is the most common form of encephalitis. You can develop viral encephalitis after having certain infectious diseases or viruses.
  • Arbovirus encephalitis: Mosquitos, fleas and ticks can spread infections that can become encephalitis.
  • Bacterial or fungal encephalitis: Encephalitis from bacterial or fungal infections is the least common type of the condition.

In autoimmune encephalitis, your immune system mistakenly attacks your brain, causing inflammation that may affect how your brain works. This sometimes happens to people with cancer. Healthcare providers call this paraneoplastic syndrome.


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Symptoms and Causes

What are encephalitis symptoms?

Symptoms vary depending on the type of encephalitis. Encephalitis from infections typically develops more quickly than autoimmune encephalitis. Early warning signs of infective encephalitis include:

Autoimmune encephalitis develops more slowly and causes neurological symptoms. These symptoms can be life-threatening if you don’t get medical help right away:

Infective and autoimmune encephalitis may be life-threatening. Call 911 (or your local emergency services number) if you have these symptoms or are with someone who has these symptoms.

What causes infective encephalitis?

The most common cause is when certain viruses affect your brain. That usually happens if you have the herpes simplex virus (HSV). But you can develop encephalitis if you have certain infectious diseases or other viruses.

Infectious disease viruses that cause encephalitis include:

Other viruses that cause the condition include:

Viruses spread by insects include:

  • Dengue viruses: There are four different dengue viruses spread via bites from infected mosquitos. Dengue viruses are common in the U.S.
  • Eastern equine encephalitis (EEE): People who live in the U.S. near the Great Lakes, the Gulf of Mexico or the Atlantic Ocean coastline have an increased risk of EEE from infected mosquitos.
  • St. Louis encephalitis (SLE) virus: This is another virus from infected mosquitos. In this case, mosquitos become infected after biting a bird carrying the SLE virus.
  • Tick-borne encephalitis (TBE): This virus is spread by bites from an infected tick. It’s common in parts of western and northern Europe and eastern and northern Asia, but not in the U.S.
  • West Nile virus: This is the most common mosquito-borne virus causing encephalitis.
  • Western equine encephalitis: This mosquito-borne virus is typically found in the western U.S. and western Canada.

What are the risk factors for infective encephalitis?

Anyone can get encephalitis, but it typically affects people who have certain viral infections or are exposed to insect-borne viruses.

Insect-borne viruses are regional, meaning you’re more likely to be exposed to certain insects — and their bites — depending on where you live. Likewise, someone who spends time outside, particularly near places with standing water, has an increased risk of being bitten by mosquitos carrying viruses that may cause encephalitis.


What are encephalitis complications?

Encephalitis may cause neurologic issues, some of which may require ongoing medical treatment and support. Complications may include:

Diagnosis and Tests

How is encephalitis diagnosed?

Healthcare providers will do a physical examination. They’ll ask about your symptoms, including how long you’ve had them. They may do the following tests:


Management and Treatment

What are treatments for encephalitis?

Healthcare providers treat the condition’s underlying cause and symptoms. Most people with encephalitis are treated in the hospital so providers can monitor their symptoms and move quickly if symptoms get worse. Treatments include:

  • Antiseizure medication: Treatment to manage seizures that autoimmune encephalitis can cause.
  • Antiviral medications: Providers often treat all viral encephalitis with acyclovir (Zovirax®).
  • Breathing assistance: People with severe encephalitis may need supplemental oxygen or support from a ventilator (mechanical ventilation).
  • Corticosteroids: Both viral and autoimmune encephalitis cause brain inflammation or swelling that puts pressure on your brain. Steroids help to reduce swelling and brain pressure
  • Enteral nutrition: Severe encephalitis may cause unconsciousness. Enteral nutrition (tube feeding) supports nutrition when you aren’t conscious.
  • Immune globulin: This medication treats autoimmune encephalitis.
  • Intravenous (IV) fluids: This is supportive care to prevent dehydration.
  • Mental health support: Encephalitis may cause memory issues and personality changes. Working with a clinical psychologist may help.
  • Physical therapy: The condition may affect balance. Physical therapy may help you develop coping strategies.
  • Plasmapheresis: This is autoimmune encephalitis treatment.
  • Speech therapy: Encephalitis may cause neurological issues that affect speech.


Can infective encephalitis be prevented?

Viral infections and viruses carried by insects are common encephalitis causes. You may be able to reduce your risk by keeping vaccinations up to date as needed and protecting yourself from mosquito bites.

Up-to-date vaccinations

Make sure you have current vaccinations against chickenpox, measles, mumps and rubella. Most people receive MMR vaccinations as children. These are one-and-done vaccinations; people don’t need to update them. But this combination vaccine wasn’t introduced until 1971. If you were born before then, ask your healthcare provider what vaccinations make sense.

Mosquito protection

Infected mosquitoes can pose a serious health risk. You can prevent mosquito bites by:

  • Wearing protective clothes: Add lightweight long-sleeve shirts and pants to your summer wardrobe. Add a hat to protect your ears.
  • Use insect repellents: Pick repellents containing DEET, and be sure to follow instructions on the repellent packaging.
  • Keep your property dry: Mosquitos lay their eggs in standing water, like water in flowerpots or open garbage cans. Dry out items and then spray them with insecticide.
  • Use screens and fans: Window screens help to keep mosquitos outside. But if they’re inside, running fans will keep mosquitos moving and less likely to land on you.

Outlook / Prognosis

How long does it take to recover from encephalitis?

You may have encephalitis symptoms for a few days up to two or three months. It can take an additional two or three months to completely recover from the condition.

Can encephalitis be cured?

Medication to treat underlying conditions, like viruses, may cure encephalitis. In some cases, however, encephalitis may cause long-term issues that require ongoing medical care. For example, people may have ongoing issues with behavior, memory loss or speech.

What is the life expectancy for someone with encephalitis?

That depends on their situation. While most people with encephalitis recover, the condition can be life-threatening. One study showed 5% of people died while in the hospital for encephalitis treatment. In general, how long you live after recovering from encephalitis depends on factors like:

  • The underlying cause: Common viruses like herpes simplex tend to cause less serious issues and, as a result, don’t have a significant impact on life expectancy.
  • The level of inflammation: Severe inflammation that causes neurological issues can affect life expectancy.
  • Age and overall health: Children have a better chance of recovery than older adults. Recovery is more challenging for people with preexisting health issues or weakened immune systems.
  • Early diagnosis and treatment: People who receive prompt treatment tend to have better outcomes, including less of a chance that this condition will have an impact on their life expectancy.

If you have encephalitis or care for someone who does, ask a healthcare provider what to expect.

Living With

How do I take care of myself?

It takes time for your brain to heal from encephalitis, so recovery is more of a marathon than a sprint. Here are some suggestions that may help you along the road to recovery:

  • Pace yourself: You may feel very tired for months after you get over encephalitis. You may need to take a break from some commitments so you can focus on high-priority activities like your family life without becoming exhausted.
  • Get your rest: Develop good sleep hygiene habits like setting regular bedtimes and cutting back on stimulants like caffeine and alcohol.
  • Maintain a healthy diet: Focus on lean protein, whole grains, leafy vegetables and fruits. The Mediterranean diet may be an option.
  • Develop an exercise routine: Regular exercise can help you to deal with the challenges of a long recovery from encephalitis.
  • Share your situation: You may look perfectly healthy even though you’re still recovering. Let your friends and family know why you’re taking life slow.

When should I see my healthcare provider?

If you have encephalitis, ask your provider about changes that may mean your condition is getting worse. And go to the emergency room anytime you have symptoms like confusion, noticeable personality changes, speech issues or weakness, or you can’t move your arms or legs.

A note from Cleveland Clinic

Encephalitis is a serious disease that can have long-term consequences. It can take months or years for you to fully recover from the condition. Unlike injuries or illnesses that affect your body, you can’t see or feel your brain beginning to heal. People may assume you’re completely recovered when you’re still working through issues, from ongoing fatigue to neurological challenges. If that’s your situation, take time to explain how encephalitis continues to affect you.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 12/18/2023.

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