Encephalitis (en-sef-uh-LIE-tis) is inflammation of the brain. Viral infections are the most common cause of the condition.
Encephalitis can cause flu-like symptoms, such as a fever or severe headache. It can also cause confused thinking, seizures, or problems with senses or movement. However, many cases of encephalitis result in only mild flu-like symptoms or even no symptoms.
Most people with viral encephalitis have either no symptoms or mild flu-like symptoms, such as the following:
- Aches in muscles or joints
- Fatigue or weakness
More-serious cases require prompt medical care. Additional signs and symptoms of more serious encephalitis may include the following:
- Confusion, agitation or hallucinations
- Loss of sensation or paralysis in certain areas of the face or body
- Muscle weakness
- Double vision
- Perception of foul smells, such as burned meat or rotten eggs
- Problems with speech or hearing
- Loss of consciousness
Signs and symptoms in infants and young children may also include:
- Bulging in the soft spots (fontanels) of the skull in infants
- Nausea and vomiting
- Body stiffness
- Inconsolable crying
- Poor feeding or not waking for a feeding
When to see a doctor
Get immediate care if you or someone you know is experiencing any of the symptoms associated with more-severe cases of encephalitis. Severe headache, fever and altered consciousness require urgent care.
Infants and young children with any signs or symptoms of encephalitis should receive urgent care.
The exact cause of encephalitis is often unknown, but the most commonly diagnosed cause is a viral infection. Bacterial infections and noninfectious inflammatory conditions also may cause encephalitis.
An infection may result in one of two conditions affecting the brain:
- Primary encephalitis occurs when a virus or other infectious agent directly infects the brain.
- Secondary (postinfectious) encephalitis is a faulty immune system reaction in response to an infection elsewhere in the body. Instead of solely attacking the cells causing an infection, the immune system also mistakenly attacks healthy cells in the brain.
Common viral causes
Common causes of encephalitis include:
- Herpes simplex virus. There are two types of herpes simplex virus (HSV). Either type can cause encephalitis.
- Other herpes viruses. Other herpes viruses that may cause encephalitis include the Epstein-Barr virus, which commonly causes infectious mononucleosis, and the varicella-zoster virus, which commonly causes chickenpox and shingles.
- Enteroviruses. These viruses include the poliovirus and the coxsackievirus, which usually cause an illness with flu-like symptoms, eye inflammation and abdominal pain.
- Mosquito-borne viruses. Arboviruses, or arthropod-borne viruses, are transmitted by mosquitoes or other blood-sucking insects. Mosquito-borne viruses can cause infections that include West Nile, La Crosse, St. Louis, western equine and eastern equine encephalitis.
- Tick-borne viruses. The Powassan virus is a well-known tick-transmitted virus that causes encephalitis in the U.S. and Canada.
- Rabies virus.
- Childhood infections. Common childhood infections — such as measles (rubeola), mumps and German measles (rubella) — used to be fairly common causes of secondary encephalitis.
Anyone can develop encephalitis. Factors that may increase the risk of the condition include:
- Some types of encephalitis are more prevalent or more severe in certain age groups. In general, young children and older adults are at greater risk of most types of viral encephalitis. Encephalitis from the herpes simplex virus tends to be more common in people 20 to 40 years of age.
- Weakened immune system.
- Geographic regions. Mosquito-borne or tick-borne viruses are common in particular geographic regions.
- Season of the year.
The complications resulting from encephalitis depend on several factors, including age, the cause of the infection, the severity of the initial illness and the time from disease onset to treatment.
In most cases, people with relatively mild illness recover within a few weeks with no long-term complications.
Complications of severe illness
Injury to the brain from inflammation can result in a number of problems. The most severe cases can result in coma or death.
Other complications — varying greatly in severity — may persist for months or be permanent:
- Persistent fatigue
- Weakness or lack of muscle coordination
- Personality changes
- Memory problems
- Hearing or vision defects
- Speech impairments
Tests and diagnosis
Questions about symptoms, risk factors and medical history are important in making a diagnosis of encephalitis. Diagnostic tests that may be needed include the following:
- Brain imaging.Technologies may include magnetic resonance imaging (MRI), which can produce detailed cross-sectional and 3-D images of the brain, or computerized tomography (CT), which produces cross-sectional images.
- Spinal tap (lumbar puncture).In some cases, samples of CSF can be tested to identify the virus or other infectious agent.
- Other lab tests. Samples of blood or urine, or of excretions from the back of the throat can be tested for viruses or other infectious agents.
- Electroencephalogram (EEG).
- Brain biopsy.
Treatments and drugs
Treatment for mild cases, which may be mistaken as the flu, mainly consists of:
- Bed rest
- Plenty of fluids
- Anti-inflammatory drugs— such as acetaminophen, ibuprofen and naproxen sodium — to relieve headaches and fever.
Cases of encephalitis due to certain viruses usually require intravenous antiviral treatments. Antiviral drugs commonly used to treat encephalitis include:
Additional supportive care also is needed in the hospital for people with severe encephalitis. The care may include:
- Breathing assistance, as well as careful monitoring of breathing and heart function
- Intravenous fluids to ensure proper hydration and appropriate levels of essential minerals
- Anti-inflammatory drugs, such as corticosteroids, to help reduce swelling and pressure within the skull
- Anticonvulsant medications, such as phenytoin (Diphedan), to stop or prevent seizures.
After the initial illness, it may be necessary to receive additional therapy depending on the type and severity of complications. This therapy may include:
- Physical therapy to improve strength, flexibility, balance, motor coordination and mobility
- Occupational therapy to develop everyday skills and to use adaptive products that help with everyday activities
- 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 — with medication management if necessary
The best way to prevent viral encephalitis is to take precautions to avoid exposure to viruses that can cause the disease:
- Practice good hygiene.
- Don’t share utensils.
- Teach your children good habits.
- Get vaccinations.
Protection against mosquitoes and ticks
To minimize your exposure to mosquitoes and ticks, follow these tips:
- Dress to protect yourself.
- Apply mosquito repellent.
- Use EPA-recommended insecticide.
- Avoid mosquitoes.
- Keep mosquitoes out of your home.
- Get rid of water sources outside your home.
- Control mosquitoes in standing water.
- Look for outdoor signs of viral disease.
Protection for young children
Insect repellents aren’t recommended for use on infants younger than 2 months of age. Instead, cover an infant carrier or stroller with mosquito netting.
Tips for using mosquito repellent with children include the following:
- Always assist children with the use of mosquito repellent.
- Spray on clothing and exposed skin.
- Apply the repellent when outdoors to lessen the risk of inhaling the repellent.
- Spray repellent on your hands and then apply it to your child’s face. Take care around the eyes and ears.
- Don’t use repellent on the hands of young children who may put their hands in their mouths.
- Wash treated skin with soap and water when you come indoors.