Health Topic

Encephalitis

Encephalitis is inflammation of the brain, often caused by a viral infection. There are several types of Encephalitis. Read about their symptoms, diagnosis, and treatment.

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Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Encephalitis

Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.

There are different types of encephalitis, based on what the cause is. The two main types are infectious encephalitis and autoimmune encephalitis.

Infectious encephalitis is usually caused by a virus. In fact, viruses are the most common cause of encephalitis. Some of the different viruses that cause it include:

  • Herpes viruses, including herpes simplex (HSV), the Epstein-Barr virus (which causes infectious mononucleosis) and the varicella-zoster virus (which causes chickenpox).
  • Viruses you can get if you are bitten by an infected tick, such as tick-borne encephalitis (TBE virus) and Powassan virus.
  • Viruses you can get if you are bitten by an infected mosquito, such as eastern equine encephalitis virus, West Nile virus, and La Crosse virus.
  • Enteroviruses, which are a common group of viruses that mostly cause mild illness or respiratory infection. These infections usually happen in the summer and fall.

Bacteria, fungi, and parasites can also cause infectious encephalitis. But this is not common.

Autoimmune encephalitis happens when your immune system mistakenly attacks healthy brain cells. It can be triggered by conditions such as certain cancers, benign tumors, and infections. Sometimes the cause is not known.

Anyone can get encephalitis, but you are more likely to get it if you:

  • Have a weakened immune system, for example from having HIV or taking certain medicines. These could include medicines taken after an organ transplant, certain chemotherapy medicines, and specialized treatments for certain autoimmune diseases.
  • Are a young child or older adult.
  • Live in areas where there are ticks and mosquitoes that carry viruses that can cause encephalitis.

The symptoms of encephalitis can vary a lot, depending on how severe it is. Many people do not have any symptoms. Others may have mild flu-like symptoms such as fever, fatigue, headache, or body aches. If encephalitis becomes more serious, it can cause:

  • Severe headache
  • Stiff neck
  • Vomiting
  • Seizures
  • Behavior changes
  • Drowsiness
  • Muscle weakness
  • Partial paralysis in your arms and legs
  • Coma

Encephalitis can be dangerous in infants. Their symptoms may include:

  • Fever
  • Lethargy (weakness or drowsiness)
  • Poor feeding
  • Vomiting
  • Body stiffness
  • Unusual irritability or crying
  • A full or bulging fontanel (the soft spot on the top of the head)

If you or your child is having symptoms of encephalitis, it's important to get medical care right away.

To find out if you have encephalitis, your health care provider:

  • Will do a physical exam
  • Will take your medical history, which includes asking about your symptoms
  • May do a neurologic exam
  • May order imaging tests, such as a brain CT scan or MRI
  • May order an EEG (electroencephalography), which use small electric sensors to measure your brain activity
  • May order blood and cerebrospinal fluid (CSF) tests

Most people with encephalitis will need treatment in the hospital. Depending on the cause, treatments may include antiviral medicines, antibiotics, corticosteroids, and other medicines.

For some types of encephalitis, there is no medicine to treat it. But rest, nutrition, and fluids can help your body fight the infection and relieve symptoms.

Some people may need physical, speech, and occupational therapy once the illness is under control.

There are steps you can take to help prevent encephalitis that is caused by infections:

  • Use good hygiene, including washing your hands often with soap and water.
  • Don't share food, drinks, utensils, and glasses with other people.
  • Get vaccines for viruses that can cause encephalitis.
  • Avoid mosquito and tick bites, for example by: Wearing insect repellent with DEET or another U.S. Environmental Protection Agency (EPA)-registered insect repellent. Make sure to follow the instructions for using the repellant.
  • Wearing clothes that cover your arms, legs and feet.
  • Treating your clothing and gear with products containing 0.5% permethrin before you go in grassy or woody areas.

It sits within Brain and Nerves.

The lead U.S. institute for this subject is the National Institute of Neurological Disorders and Stroke.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Encephalitis

429 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

Start Here

Diagnosis and Tests

Treatments and Therapies

Prevention and Risk Factors

Statistics and Research

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Encephalitis. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Encephalitis, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.