Understanding Encephalitis: The Basics

Medically Reviewed by Poonam Sachdev on February 28, 2024
10 min read

Encephalitis (pronounced en-sef-uh-lie-tis) is inflammation of your brain tissue. It can be very serious and may cause personality changes, seizures, weakness, and other symptoms, depending on the part of your brain affected.


Encephalitis is rare, affecting about 10-15 in 100,000 people each year in the U.S. Young children, older adults, and those with a weak immune system are most vulnerable.

It's usually caused by an infection with viruses, bacteria, fungi, or parasites, although it can be caused by an autoimmune condition or some medicines as well.

Most people who have mild encephalitis fully recover. Your treatment and chance of recovery depend on the cause and severity of your inflammation.

In acute encephalitis, the infection directly affects your brain cells. In parainfectious encephalitis, your brain and spinal cord become inflamed within 1-2 weeks of contracting an infection (usually viral or bacterial).

Encephalitis vs. meningitis

Encephalitis and meningitis are both diseases that cause inflammation in your brain. However, while encephalitis is an inflammation of your brain tissue, meningitis is an inflammation of the membranes that cover your brain and spinal cord (called meninges). Like encephalitis, meningitis is often caused by a viral or bacterial infection, but it can also be caused by fungal or parasitic infections, injuries, certain drugs, and some types of cancer.

Is encephalitis contagious?

Swelling in your brain isn’t contagious, but the causes can be. For example, viral encephalitis can be caused by the herpes simplex virus (HSV) that can pass from person to person. Childhood diseases, such as measles, mumps, and German measles (Rubella), used to be a common cause of viral encephalitis in kids, but these causes are a bit rarer now since most people get vaccinated against them before they start school.

Viral infections with any of the following three groups of viruses are the most common cause of encephalitis. These include:

  • Herpes viruses, which include HSV (especially HSV-1), chickenpox, cytomegalovirus, and Epstein-Barr virus
  • Viruses that are transmitted through bugbites, such as West Nile virus, Dengue virus, and Eastern equine encephalitis virus
  • Viruses that cause childhood infections, such as measles, mumps, and Rubella

Less commonly, encephalitis may be caused by:

  • Infection with HIV or the virus that causes rabies
  • Bacterial and other infections, such as syphilis or toxoplasmosis (an infection with a parasite from infected cat poop)
  • Autoimmune conditions
  • Some kinds of cancer
  • Some medicines

Sometimes, your doctor may not be able to tell what caused your encephalitis.

Infectious encephalitis

It is usually caused by a viral infection but can also be caused by bacteria, fungi, and parasites.

As it's usually caused by viral infections, it's more common in people who are exposed to bugs that can transmit diseases, such as people who spend a lot of time outdoors, especially near standing water.

Infectious encephalitis can develop quickly and the symptoms can be serious.

Autoimmune encephalitis

It is usually caused by proteins that your body makes in your brain. These proteins cause inflammation in your brain. Doctors don't yet know for sure why some people develop these proteins, while other people don't.

Autoimmune encephalitis tends to develop more slowly than infectious encephalitis and may cause more neurological symptoms, such as confusion, memory issues, and seizures. It's also rarer than infectious encephalitis.

Some conditions that are linked to autoimmune encephalitis include:

  • Acute disseminated encephalomyelitis (ADEM)
  • Anti-NMDA receptor encephalitis
  • Hashimoto’s encephalopathy
  • LGI1/CASPR2-antibody encephalitis
  • Limbic encephalitis
  • Rasmussen’s encephalitis

Both infectious and autoimmune encephalitis can cause serious, life-threatening symptoms. If you or someone else has neurological symptoms, such as irritability, seizures, or extreme drowsiness, call 911 or go to the emergency room right away.

Your symptoms depend on the type of encephalitis you have. People with infectious encephalitis may have symptoms of an infection before they get encephalitis.

Signs of encephalitis can include:

  • Fatigue or loss of energy
  • Fever, especially a high fever
  • Headache that can be severe
  • Sensitivity to light and sound
  • Mild-to-moderate neck stiffness
  • Drowsiness or loss of consciousness
  • Irritability, anxiety, and behavioral or personality changes
  • Hallucinations

Signs of severe encephalitis may include:

  • Weakness or trouble moving some parts of your body
  • Double vision
  • Confusion, trouble speaking, or difficulty understanding when someone talks to you 
  • Coma
  • Seizures
  • A bulging soft spot (fontanel) in infants

Go to the ER or call 911 right away if you or someone else has any signs of severe encephalitis.

Your doctor will ask about your symptoms, including how long you've had them. Because people with encephalitis can be disoriented, family and friends are key to getting a good history. It's important to know if you've come into contact with mosquitoes or ticks, infected animals, or sick people.

Your doctor will also do a physical exam and may order some tests.

Encephalitis tests

Some of the tests your doctor may use include:

  • Blood tests, including a complete blood count and comprehensive metabolic panel
  • Urine, stool, or sputum culture tests to see if you have an infection and what type you have
  • Imaging tests, such as CT scans, MRI scans, and magnetoencephalography (MEG) to see where in your brain you are having seizures
  • Electroencephalogram (EEG) to look for seizers or specific electrical activity in your brain
  • Spinal tap (lumbar puncture) to remove cerebrospinal fluid to find infections in your brain or spinal cord
  • A neurological exam, which is a series of tests that show how well your nervous system is working
  • An intracranial pressure monitoring (ICP) to measure the pressure inside your skull
  • Rarely, a biopsy of your brain tissue to look at under a microscope

Several risk factors could increase your chance of getting encephalitis. These include:

  • Age. Young children and older adults are at a higher risk for viral encephalitis. Some types of autoimmune encephalitis are more common in children and young adults.
  • Having a weakened immune system. This could be because you have HIV, take medicines for cancer, or have a condition such as diabetes.
  • Having an autoimmune condition.
  • Smoking.
  • Living in areas where mosquito- or tick-borne viruses spread easily, particularly in the summer months.

Because the complications from encephalitis can be serious, you may need to go to the hospital. You will usually need monitoring for your blood pressure, heart rate, and breathing. You will also usually need IV fluid therapy to help keep your brain from swelling more. 

Otherwise, your treatment will depend on your age, condition, and the cause of your disease.

Some common treatments include:

  • Steroids that can help reduce swelling in your brain
  • Antiviral drugs, such as acyclovir (Zovirax), Foscarnet (Foscavir), or Ganciclovir (Cytovene) for people who have viral encephalitis
  • Antibiotics for people with bacterial encephalitis
  • Anticonvulsant therapy for people with seizures
  • Immune globulin and plasmapheresis for people with autoimmune encephalitis
  • Over-the-counter medicines, such as acetaminophen, that can help control fever and headaches

Supportive care

Supportive care is a type of care for patients who are seriously ill. The goal is to focus your treatment on what is most important to you. This may involve, for instance, focusing on relieving your symptoms and how other treatments will affect how you feel. You usually get supportive care alongside specific treatments for your condition.

Examples of supportive care may include:

  • Use of a ventilator or other breathing help, such as an oxygen mask
  • IV fluids to keep you hydrated
  • Medications for pain, inflammation, infection, seizures, and other issues

Post encephalitis therapy

Once you have been treated for encephalopathy and the inflammation is gone, you may still need some treatment and support to continue your recovery. Some people need help such as:

  • Physical therapy to help regain your muscle strength to stand, walk, or perform regular tasks.
  • Occupational therapy (OT), which often works hand in hand with physical therapy. OT helps you work on your everyday skills and may give you ideas for adaptations, such as special tools, if you need help with some of your day-to-day activities.
  • Speech therapy, which helps you regain or fine-tune your ability to speak or communicate clearly.
  • Brain rehabilitation or retraining, which helps you improve your memory and your cognition.
  • Psychotherapy, which helps you learn how to cope with changes in your life and manage your moods and behavior.

After you recover from the swelling in your brain, from encephalitis, you may have long-term damage in your brain that needs ongoing medical care. For instance, some people may have long-term problems, such as:

  • Memory loss (amnesia)
  • Personality and behavioral changes
  • Emotional and psychological problems, such as anxiety, depression, and mood swings
  • Problems with attention, concentration, planning, and problem-solving
  • Repeated seizures (epilepsy)
  • Hearing loss
  • Speech and language problems
  • Problems swallowing
  • Problems with balance, coordination, and movement
  • Long-term fatigue
  • In severe cases, loss of consciousness (coma) and death

The best way to avoid getting encephalitis is to avoid the germs that can cause it. Here are some tips:

Get yourself and your kids vaccinated, as recommended by your doctors. The elimination of smallpox and the availability of vaccines that prevent mumps, measles, and rubella have lowered cases of encephalitis, especially in children. If you're traveling in an area that has a high risk of tick-borne or mosquito-borne viruses, make sure you get vaccinated before you head out. The CDC's website has a travelers' health page where you can look up your destination and get a list of all the recommended vaccines for that location.

Wash your hands completely and often with soap and water throughout your day, especially before you handle food, eat or drink, and after using the bathroom.

Don't share food, eating utensils, or glasses.

Don't share personal-care items and remind your kids not to share their things, such as razors, towels, makeup, or toothbrushes.

Take these steps to avoid getting bitten by mosquitoes and ticks:

  • Avoid being outside between dusk and dawn when mosquitoes are most likely to bite you. If do have to be out then, wear long-sleeved shirts and long pants. Make sure mosquitoes can't get into your house through broken screens and windows. Also, run a fan, which can keep mosquitos moving around so they're less likely to land on and bite you.
  • Wear long-sleeved shirts and long pants when you're in wooded areas with tall grasses and shrubs, where ticks like to hang out. Check yourself, your kids, and your pets for ticks when they come inside during tick season (this can be year-round for people in the U.S. South and on the West Coast, but for most of the U.S., it's early spring to winter).
  • Use bug repellent and insecticide. You can use the mosquito repellent DEET on both your skin and clothes. The U.S. Environmental Protection Agency (EPA) recommends spraying your clothes, tents, and outdoor gear with products that contain permethrin to repel and kill both mosquitoes and ticks. Don't spray permethrin on your skin, though.
  • For infants younger than 2 months, you can't use insect repellent, so cover their carrier or stroller with mosquito netting. For infants and children older than 2 months old, you can use 10%-30% DEET products. Don't use a combined sunscreen and DEET product because you'll need to reapply sunscreen for a full day of outside play. Reapplying a DEET-containing product can expose your child to high levels of DEET.
  • Get rid of standing water outside your house. Mosquitoes lay their eggs in standing water. Common problem areas for standing water are old flowerpots, flat roofs, old tires, and clogged gutters.
  • Report any sick or dying birds or small animals to your local health department. They could be infected with viruses such as West Nile virus that cause encephalitis.

Your symptoms can last anywhere from a few days to a couple of months. Some people with complications may take another few months to fully recover.

However, with treatment, most people recover from encephalitis. Your outlook depends on a few things, such as:

  • What caused your encephalitis. Some causes, such as an HSV infection, may cause fewer issues, so people with encephalitis caused by HSV may have an easier recovery than other people.
  • Your level of inflammation. High levels of brain inflammation can cause more long-term issues that complicate your recovery.
  • Your age. Adults may have a harder time recovering from encephalitis.
  • Your overall health. If you have preexisting health issues or a weakened immune system, it can make your recovery more difficult.
  • How long it took you to be diagnosed. The longer it takes you to get treatment, the higher your chance of having a difficult recovery and lasting complications.

Encephalitis is a condition that involves inflammation and swelling in your brain. It's usually caused by infection with a virus, especially HSV. It isn’t always preventable, but you can lower your risk by avoiding infection with a germ that could lead to encephalitis. This means getting your recommended vaccines and avoiding or protecting yourself when in areas that have ticks and mosquitoes. If you have signs or symptoms of encephalitis, you should get to the doctor right away. Quick diagnosis and treatment can make your recovery easier and limit lasting effects. Although some people do experience complications, most people fully recover.

What is the life expectancy of people with encephalitis?

Most people fully recover from encephalitis and go on to live a normal life. People with mild cases may recover in a week, while people with serious cases may have complications that take months of added recovery time. One study showed that about 5% of people who are hospitalized with encephalitis die while they are in the hospital.

Can encephalitis resolve on its own?

If you have mild encephalitis, it can recover on its own over several weeks. Severe cases of encephalitis, however, can be life-threatening. You can't necessarily tell from your symptoms how serious your case is, so if you suspect you have encephalitis, you need to go to the doctor.