What is encephalitis?

Encephalitis is an inflammation of the brain, caused by an infection or by the immune system attacking the brain in error. It’s a serious condition requiring timely diagnosis and prompt treatment to decrease the risk of complications becoming permanent, or causing death. Although diagnosis and treatment of encephalitis has improved a great deal, about 10% of patients still die from the disease.

There are several types of encephalitis with different causes, ranging from a viral infection (the most common cause) to an attack by the immune system. Encephalitis affects different people in very different ways. The severity of the disease varies from a mild case with flu-like symptoms to life-threatening symptoms such as seizures, loss of sensation and coordination, and mental confusion. Symptoms vary according to what areas of the brain are affected. 

Both the acute stage and the recovery process can be overwhelming for patients and their families. About 25,000 Americans are hospitalized annually with encephalitis, and another 150,000+ have milder symptoms that don’t require acute hospital care.


What causes encephalitis?

The inflammation caused by encephalitis can be the result of an infection that invades brain tissue (infectious encephalitis), or by the immune system attacking the brain in error (post-infectious or autoimmune encephalitis). 

Infectious encephalitis (also called primary encephalitis) is most often caused by a virus that directly infects the brain. The infection may be concentrated in one area or widespread. Symptoms develop within days to weeks. Some of the most common encephalitis-causing viruses include herpes simplex types 1 and 2, Epstein-Barr, varicella-zoster, enteroviruses, mosquito-borne viruses (West Nile, Japanese, La Crosse, St. Louis, Powassan, Zika, Chikungunya, and both Western and Eastern equine), and tick-borne viruses. Rabies virus infection causes rapid onset of encephalitis, although rabies is a rare cause in the United States (US). 

While any virus can potentially cause encephalitis, not everyone who has a viral infection will develop encephalitis. Although rare, bacteria, fungi or parasites can cause encephalitis. Noninfectious inflammatory conditions can also cause encephalitis. The exact cause of an individual case of encephalitis is often unknown. 

Autoimmune encephalitis (also called secondary, or post-infection encephalitis) is the result of a faulty immune-system reaction to an infection in another part of the body. Instead of attacking only the cells causing the infection, the immune system also attacks healthy brain cells. These infections can result from a reactivation of a virus that became inactive after a previous illness. The reaction occurs (and symptoms develop) two to three weeks after the initial infection. Common childhood infections (measles, mumps, chickenpox, German measles) used to be fairly common causes of secondary encephalitis. Those cases are now rare in the US because of the availability of vaccinations for these diseases. 

Autoimmune encephalitis can also be caused by specific antibodies in blood that attack the brain. Antibodies are proteins that identify and remove foreign viruses and bacteria. Why these antibodies are produced by patients with autoimmune encephalitis is not known. In some cases, they can be caused by a tumor.

Who’s most at risk for encephalitis?

Although anyone can develop encephalitis, these factors can increase your risk:

  • Age – viral encephalitis is more severe in young children and older adults
  • A weak immune system caused by immune-suppressing drugs, HIV/AIDS, or other conditions
  • Travel to parts of the world where mosquito- and tick-borne viruses are more common
  • Warm weather tends to increase mosquito- and tick-borne infections

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What are the symptoms of encephalitis?

Most people with viral encephalitis have mild flu-like symptoms, such as fatigue, weakness, headache, fever, and muscle aches. Their illness lasts a few weeks with no long-term complications.

In more severe cases, symptoms can include partial paralysis in arms and legs, double vision, speech or hearing impairment, and a change in the level of consciousness, ranging from mild confusion or drowsiness, to loss of consciousness and coma. They can develop hours to days or weeks after the initial infection. 

Other symptoms include:

In infants and young children, symptoms may include:

  • Bulging in the soft spots (fontanels) of an infant's skull
  • Nausea and vomiting
  • Body stiffness
  • Poor feeding or not waking for a feeding
  • Irritability

Without treatment, encephalitis can cause complications that can last months or become permanent. Complications vary according to your age, cause of infection, severity of the inflammation, and how long before you received treatment. There may be lasting damage after recovery from the acute phase of encephalitis. 

Complications can include:

  • Acquired brain injury (ABI) caused by damaged or destroyed nerve cells in the brain
  • Persistent fatigue
  • Recurring headaches
  • Weakness or lack of muscle coordination
  • Lack of sensation on one side of the body
  • Lack of control over bodily functions
  • Paralysis
  • Hearing or vision defects
  • Blindness 
  • Speech impairment
  • Epileptic seizures
  • Personality changes
  • Aggression
  • Memory problems
  • Inability to concentrate
  • Slowed ability to think and react
  • Mood swings
  • Damaged social relationships
  • Difficulties returning to work or school
  • Coma
  • Death


How is encephalitis diagnosed?

It’s very important to get an accurate diagnosis because encephalitis symptoms can resemble other conditions. Your doctor will take your medical history and do a physical exam. He or she will need to know about your vaccinations, recent infections, where you’ve traveled recently, and if you’ve recently had a tick bite. 

Additional testing may include:

  • Brain imaging (MRI or CT scan) to check for swelling in the brain or a tumor
  • Spinal tap to look for signs of infection and inflammation in the brain
  • Blood, urine and sputum tests
  • Electroencephalogram (EEG) will look for seizures or other abnormal brain-wave patterns


How is encephalitis treated?

Prompt treatment of the underlying cause of your encephalitis is essential to survive encephalitis. Treatment is sometimes started before a definite cause is found. You should seek immediate medical care if you have a severe headache, fever, and altered consciousness. You may be admitted to a hospital’s intensive care unit to monitor you for seizures, brain swelling, heart rhythm changes or respiratory failure. 

Your treatment plan will depend on the underlying cause, your symptoms and how long you’ve had symptoms.

Mild encephalitis may be treated with bed rest, plenty of fluids, and anti-inflammatory medications such as acetaminophen, ibuprofen, or naproxen sodium for headache and fever. Mild cases of encephalitis are usually short and result in a full recovery. 

More serious cases may require these treatments:

  • Antiviral medications 
  • Antibiotics 
  • Seizure control medications
  • Immunotherapy (steroids, intravenous antibodies, or plasma exchange) for some types of autoimmune encephalitis
  • If the patient has lost consciousness, a breathing tube, urinary catheter, or feeding tube may be necessary
  • Sometimes a patient is placed in a temporary, induced coma to shut down the brain and allow time to recover from the swelling

Treatment for complications may require additional therapy. The brain takes much longer to recover from an injury than any other part of the body. Recovery can be a long and slow process and should not be rushed. It may require:

  • Physical therapy to improve strength, flexibility, balance, motor coordination and mobility
  • Occupational therapy to learn new skills, habits and strategies to cope with your remaining deficits
  • Speech therapy to relearn muscle control and coordination to produce speech
  • Psychotherapy to learn coping strategies and new behavioral skills to improve mood disorders or address personality changes

Encephalitis can be an invisible disability which affects not only the patient but their whole family. Emotional support for the whole family may be needed.

Can encephalitis be prevented?

To help prevent this potentially devastating disease, follow these recommendations:

  • Keep all vaccinations up-to-date
  • Avoid exposure to mosquito and tick bites with repellents, and staying indoors from dusk to dawn, when mosquitoes are most active
  • Eliminate standing water sources outside, where mosquitoes lay their eggs
  • Maintain good hygiene and hand-washing to protect yourself from viruses and bacteria
  • Don’t share personal items, eating utensils, or food and beverages
  • If you’re exposed to bacterial encephalitis, ask your doctor if you need antibiotics to prevent getting the disease
  • Patients who have seizures but don’t respond to anti-seizure medications can benefit from a ketogenic diet, high in fat and protein but low in carbohydrates


Johns Hopkins Medicine. (N.d.) Encephalitis. Retrieved 1-27-22, {https://www.hopkinsmedicine.org/health/conditions-and-diseases/encephalitis#:~:text=Encephalitis%20is%20inflammation%20of%20the,light%2C%20mental%20confusion%20and%20seizures.}
Encephalitis Society. (N.d.) What is Encephalitis? Retrieved 1-27-22, {https://www.encephalitis.info/what-is-encephalitis}
Mayo Clinic. (2020, April). Encephalitis. Retrieved 1-27-22, {https://www.mayoclinic.org/diseases-conditions/encephalitis/symptoms-causes/syc-20356136}
Mayo Clinic. (2020, April). Encephalitis Diagnosis and Treatment. Retrieved 1-27-22, {https://www.mayoclinic.org/diseases-conditions/encephalitis/symptoms-causes/syc-20356136}


Medically reviewed by:

Dr. Desiree Levyim

Dr. Desiree Levyim is a board eligible neurologist in practice since 2020. She joins TeleMed2U in our mission to provide increased access to healthcare.

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