What Is Encephalitis?

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Encephalitis is an infection or inflammation of the brain. It interferes with brain function, resulting in symptoms like behavioral changes, convulsions, and loss of consciousness, as well as causing other focal neurological deficits. After recovering from encephalitis, a person can have prolonged residual effects, such as epilepsy, muscle weakness, and altered mood. Prompt diagnosis and immediate treatment can improve the outcome and prevent lasting brain damage and disability.

Physical therapy after encephalitis
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Encephalitis Symptoms 

Encephalitis may start gradually, but it can worsen rapidly. It often begins with non-specific signs such as fevers, lethargy, and trouble concentrating.

While it isn’t a hard and fast rule, infectious encephalitis tends to be acute, with rapidly progressive and very noticeable, distressing effects. Inflammatory encephalitis associated with underlying autoimmune disease can be chronic, with more subtle effects. 

Signs of encephalitis can include:

  • Fevers 
  • Headaches 
  • Diminished concentration
  • Ear pain 
  • Difficulty hearing 
  • Neck stiffness 
  • Sleepiness 
  • Mood and behavior changes, including withdrawing from others or agitation 
  • Nausea and vomiting 
  • Severe dizziness and/or trouble with balance 
  • Weakness of the arm or leg in one side of the body
  • Altered sensations, such as tingling, numbness, or pain
  • Impaired vision
  • Distorted sense of smell
  • Confusion 
  • Aggression
  • Hallucinations
  • Seizures 
  • Breathing difficulties
  • Loss of consciousness

With chronic encephalitis, concentration, mood, and personality changes may be more prominent than the neurological issues like seizures or weakness.

Encephalitis can be fatal if it spreads widely in the brain or affects areas of the brain that control the heart and/or respiratory function.


Complete recovery is possible. But long-term brain damage can occur after encephalitis resolves, with residual effects. The condition can cause brain necrosis (tissue death) or stroke, permanently impairing the affected areas of the brain. 

Brain tissue necrosis can occur due to the direct effects of inflammation, injury from an infection, or as the result of a stroke. Encephalitis can cause a stroke by disrupting blood flow in the brain. An encephalitis-associated stroke can be ischemic (due to a lack of blood supply to an area of the brain) or hemorrhagic (due to bleeding in the brain). 

After recovering from encephalitis, the consequences can lead to long-term problems that affect thinking, vision, speaking, muscle strength, or mood, and can cause recurrent seizures.


A number of risk factors can increase the chances of developing encephalitis. A weak immune system resulting from an immune deficiency or immunosuppressants can predispose you to infectious encephalitis. And medical interventions that produce inflammation of the brain, like radiation therapy for cancer, can induce inflammatory encephalitis. 

Autoimmune disease and chemotherapy, which may predispose someone to inflammatory encephalitis, are also associated with immune deficiency, and may increase the risk of infectious encephalitis as well. And congenital (from birth) encephalitis, while rare, can cause lifelong effects.

Infectious Encephalitis 

Brain infections are rare, but there are certain infectious organisms that tend to be identified as the cause of these types of infections.

In general, the brain tissue is shielded from infections by the meninges (a type of covering that envelopes and protects the brain). And another type of protection described as the blood-brain barrier is due to the structure of the blood vessels in the brain, which are not easy for infectious microorganisms (like bacteria and viruses) to penetrate.

Nevertheless, meningitis, which is an infection or inflammation of the meninges, can occur. Meningitis can spread to the brain, causing encephalitis, especially if you have a weak immune system. Sometimes an infection can spread to the brain through the blood vessels, a situation that’s made more likely when you have a weak immune system. 

Some infectious types of encephalitis are mosquito- or tick-borne, which means that they are transmitted through these insect bites. And others are transmitted from person to person through the air or through food.

Infections that can cause encephalitis include: 

Bacteria: Meningococcus and pneumococcus. Group A beta-hemolytic streptococcal infection can cause Syndenham chorea, a type of encephalitis that affects children, causing unusual movements. It generally resolves, although it can cause long-term behavior changes in some children.

Viruses: Rabies is transmitted by dog bites. West Nile virus and chikungunya virus are transmitted by mosquitoes. Flaviviruses are spread by tick bites. Herpesviruses, HIV virus, measles virus, varicella-zoster virus (the virus that causes chickenpox), and enterovirus are a few of the potentially encephalitis-causing viruses that are transmitted from person to person.

Progressive multifocal leukoencephalopathy (PML): This is a severe brain infection caused by the reactivation of the otherwise harmless John Cunningham (JC) virus, usually as a result of treatment with powerful immunosuppressants.

Parasites: Malaria and cysticercosis are parasitic worms that can infect the brain. Toxoplasma is a single-cell parasite that can infect the brain.

Fungus: Fungal infections can infect the nervous system. For example, histoplasmosis and candida are fungal infections that can cause encephalitis if a person is severely immunocompromised.

Sepsis or septicemia: Septicemia is a blood infection (usually bacterial) and sepsis is the body’s inflammatory response to a severe blood infection. Infectious or non-infectious encephalitis can occur with sepsis or septicemia, typically resulting in severe systemic effects, as well as the effects on the brain.

Non-Infectious Encephalitis 

Encephalitis can be due to an inflammatory disease that involves the brain, or inflammation can develop in response to medical treatment. 

Non-infectious conditions that cause encephalitis include: 

COVID-19 associated encephalitis has been described with acute coronavirus infection. This condition can manifest with loss of smell sensation, confusion, and hallucinations. Experts are still learning about the symptoms and have not yet determined whether it is an effect of the virus, or an inflammatory response to the virus.


Identifying encephalitis is not simple. That is because it is not easy to verify that a person has an infection or inflammation of the brain. Diagnosis is based on a combination of clinical signs, physical examination, blood tests, brain imaging, and possibly specialized testing like lumbar puncture or electroencephalogram (EEG). Rarely, a brain biopsy is obtained as well. 

Physical Examination 

If you have encephalitis, it can affect your vital signs. You may have a fever, tachycardia (rapid heart rate) or bradycardia (slow heart rate). You can also have tachypnea (fast breathing) or you might not be breathing adequately. 

Other signs that may be noted on a physical examination include weakness or stiffness of the muscles, and confusion or decreased attention. Involuntary jerking of the arms or legs, difficulty with balance, or unusual eye movements can be present as well.

One of the most noticeable signs of encephalitis in babies is an enlarged fontanelle, which is a fullness or bulging of the top of the head where the skull hasn’t formed yet.

Sometimes encephalitis that started as bacterial meningitis can also be accompanied by a skin rash.

An eye examination, including an examination of the back of the eyes with a fundoscope, may show increased pressure behind the eye or changes in the shape of the blood vessels in the eye. This is a sign that there is increased pressure inside the skull caused by encephalitis and that urgent treatment to reduce the pressure is needed.

Blood Tests 

You will likely have blood tests. A blood test can identify problems like sepsis or septicemia, and it may identify a microorganism that is causing infectious encephalitis. However, with infectious encephalitis, the microorganism may be limited to only the brain and might not be detected with a blood test.

Blood tests may also indicate signs of acute inflammation (such as with ADEM) or that a systemic inflammatory condition (like SLE) is acting up and could be associated with the symptoms of encephalitis. 

Imaging Tests 

Brain imaging tests such as computerized tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET) can show changes in the brain that are consistent with an infection or inflammation. These tests can show signs of inflammation, one or more abscesses (confined areas of infection), or a parasite.

Brain imaging tests can also show cancer and strokes that can be complicated by inflammation.

Edema is swelling that can be produced by inflammatory cells or fluid, and may be observed on these tests as well. Localized areas of edema or edema throughout the brain can occur with encephalitis. Edema is often a sign that there is pressure in the brain, which may compress and damage healthy areas. Edema is among the effects of encephalitis that needs to be treated urgently.

Specialized Tests 

A number of specialized tests might be needed to help determine whether you have encephalitis and to identify the cause.

Electroencephalogram (EEG): This is a non-invasive test that produces a wave tracing of the brain’s electrical activity. This test can help support a diagnosis of encephalitis if the waves are distorted, although there are other causes of altered EEG patterns besides encephalitis. 

Lumbar puncture (LP): Also referred to as spinal tap, lumbar puncture is an invasive test in which a needle is inserted in the lower back to sample spinal fluid. The fluid pressure is measured (an increase can signal inflammation or edema) and the sample is tested for red blood cells (a sign of bleeding, which can accompany encephalitis), white blood cells (which indicate infection or inflammation), and infectious microorganisms.

With an LP, the results don’t distinguish between meningitis and encephalitis, but they do show whether an infection or inflammation has involved the spinal fluid.

Brain Biopsy 

This is not a common test. A brain biopsy requires a surgical procedure. It is invasive and poses a risk of bleeding in the brain, so it is only performed if brain surgery is necessary for therapeutic relief, or if the condition is not improving with treatment that is based on other diagnostic testing.

A brain biopsy sample can be examined under a microscope to identify signs of inflammation or infection in the brain tissue, which can help direct treatment.

Encephalitis and Encephalopathy 

It can be difficult to distinguish encephalitis from encephalopathy, which is brain dysfunction. Encephalopathy is caused by metabolic problems, like liver failure or chronic alcohol toxicity. It may cause symptoms similar to those of encephalitis, but inflammation is not a prominent feature and the treatment is different than that of encephalitis. 


Management of encephalitis requires a multifaceted approach aimed at reducing the long-term effects of the disease and the risk of death. The immediate phase of treatment is focused on preventing life threatening issues like respiratory failure and reducing brain damage due to a stroke or edema.

If you are having trouble breathing, you might need emergency oxygen supplementation or mechanical respiratory support

Treatment of the cause of encephalitis is the priority. And controlling issues like seizures or agitation is important for preventing physical injury and further brain deficits.

Managing Edema

Edema of the brain may be controlled with fluid management and anti-inflammatory steroids. This is usually a very delicate process in which fluid and steroids are administered intravenously (IV, in a vein) and the concentration of electrolytes is carefully and meticulously measured to avoid overhydration or underhydration—both of which may contribute to edema.

An LP may be performed to remove fluid as a way to reduce the pressure-inducing effects of edema on the brain. In some situations, surgery may be needed to relieve the pressure of swelling. Another type of procedure involves removing part of the skull as the edema subsides and replacing it at a later time. 

Sometimes a shunt is placed in the brain to continuously prevent edema from building up again after surgery. A shunt may remain in place for years after recovery from an episode of encephalitis if edema continues to be a problem.

Your healthcare providers may treat your edema with anti-inflammatory treatments. It can be tricky, but these treatments can increase the risk of infection or worsen an already existing infection. You will be closely monitored for signs of an infection throughout your encephalitis treatment.


An infection will likely be treated with an IV antimicrobial targeted to the specific infection. Rarely, the treatment might be administered intrathecally (into the spinal fluid). And sometimes surgical treatment is needed to remove a tumor or an abscess in the brain that is associated with encephalitis. 

Inflammatory or autoimmune encephalitis may be treated with immunosuppressive therapy, potentially for the long term.

Other treatments include medications to lower a fever, anti-seizure medication, antipsychotics to control agitation or hallucinations, and blood thinners if there is a blood clot in the brain.


After recovery from encephalitis, you might need to re-learn skills that have been impaired by the condition's effects on the brain. Working with your medical team to regain your balance or strength, learn to communicate again, or recognize mood changes can all be a part of your rehabilitation and recovery.

You will likely need physical therapy and occupational therapy to help you improve your strength and self-care skills. You might also need speech and swallow therapy so you can learn to swallow food and drink safely.

Sometimes counseling might be beneficial to help you work through psychological and emotional consequences of encephalitis. The recovery process can take months or even years. 

A Word From Verywell

Encephalitis is not common, and if you or a loved one has this serious brain condition, it can be stressful. While the condition can be treated, you may have a long road to recovery. Understanding your condition and talking with your medical team about setting goals and expectations throughout your recovery can be helpful.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.