Encephalitis
Encephalitis is irritation and swelling (inflammation) of the brain, most often due to infections.
Causes
Encephalitis is a rare condition. It occurs more often in the first year of life and decreases with age. The very young and older adults are more likely to have a severe case.
Encephalitis is most often caused by a virus. Many types of viruses may cause it. Exposure can occur through:
- Breathing in droplets from the nose, mouth, or throat from an infected person
- Contaminated food or drink
- Mosquito, tick, and other insect bites
- Skin contact
Different viruses occur in different geographic locations. Many cases occur during a certain season.
Encephalitis caused by the herpes simplex virus is the leading cause of more severe cases in all ages, including newborns.
Routine vaccination has greatly reduced encephalitis due to some viruses, including:
- Measles
Measles
Measles is a very contagious (easily spread) illness caused by a virus.
Read Article Now Book Mark Article - Mumps
Mumps
Mumps is a contagious disease that leads to painful swelling of the salivary glands. The salivary glands produce saliva, a liquid that moistens food...
Read Article Now Book Mark Article - Polio
Polio
Polio is a viral disease that can affect nerves and can lead to partial or full paralysis. The medical name for polio is poliomyelitis.
Read Article Now Book Mark Article - Rabies
Rabies
Rabies is a deadly viral infection that is mainly spread by infected animals.
Read Article Now Book Mark Article - Rubella
Rubella
Rubella, also known as the German measles, is an infection in which there is a rash on the skin. Congenital rubella is when a pregnant woman with rub...
Read Article Now Book Mark Article - Varicella (chickenpox)
Varicella
Chickenpox is a viral infection in which a person develops very itchy blisters all over the body. It was more common in the past. The illness is ra...
Read Article Now Book Mark Article
Other viruses that cause encephalitis include:
- Adenovirus
- Coxsackievirus
- Cytomegalovirus
Cytomegalovirus
Cytomegalovirus (CMV) infection is a disease caused by a type of herpes virus.
Read Article Now Book Mark Article - Eastern equine encephalitis virus
- Echovirus
- Japanese encephalitis, which occurs in Asia
- West Nile virus
West Nile virus
West Nile virus causes a viral disease and is spread by mosquitoes. The condition ranges from mild to severe.
Read Article Now Book Mark Article
After the virus enters the body, the brain tissue swells. This swelling may destroy nerve cells, and cause bleeding in the brain and brain damage.
Other causes of encephalitis may include:
- An allergic reaction to vaccinations
- Autoimmune disease
Autoimmune disease
An autoimmune disorder occurs when the body's immune system attacks and destroys healthy body tissue by mistake. There are more than 80 autoimmune d...
Read Article Now Book Mark Article -
Bacterial infections such as Lyme disease, syphilis, and tuberculosis
Lyme disease
Lyme disease is a bacterial infection that is spread through the bite of one of several types of ticks.
Read Article Now Book Mark ArticleSyphilis
Syphilis is a bacterial infection that is most often spread through sexual contact.
Read Article Now Book Mark Article -
Parasites such as roundworms, cysticercosis, and toxoplasmosis in people with HIV/AIDS and other people who have a weakened immune system
Cysticercosis
Cysticercosis is an infection by a parasite called Taenia solium (T solium). It is a pork tapeworm that creates cysts in different areas of the body...
Read Article Now Book Mark ArticleToxoplasmosis
Toxoplasmosis is an infection due to the parasite Toxoplasma gondii.
Read Article Now Book Mark ArticleHIV/AIDS
Human immunodeficiency virus (HIV) is the virus that causes acquired immunodeficiency syndrome (AIDS). When a person becomes infected with HIV, the ...
Read Article Now Book Mark Article - The effects of cancer
Symptoms
Some people may have symptoms of a cold or stomach infection before encephalitis symptoms begin.
When this infection is not very severe, the symptoms may be similar to those of other illnesses:
- Fever that is not very high
Fever
Fever is the temporary increase in the body's temperature in response to a disease or illness. A child has a fever when the temperature is at or abov...
Read Article Now Book Mark Article - Mild headache
Headache
A headache is pain or discomfort in the head, scalp, or neck. Serious causes of headaches are rare. Most people with headaches can feel much better...
Read Article Now Book Mark Article - Low energy and a poor appetite
Other symptoms include:
- Clumsiness, unsteady gait
- Confusion, disorientation
Confusion
Confusion is the inability to think as clearly or quickly as you normally do. You may feel disoriented and have difficulty paying attention, remembe...
Read Article Now Book Mark Article - Drowsiness
Drowsiness
Drowsiness refers to feeling more sleepy than normal during the day. People who are drowsy may fall asleep when they do not want to or at times whic...
Read Article Now Book Mark Article - Irritability or poor temper control
- Light sensitivity
- Stiff neck and back (sometimes)
- Vomiting
Vomiting
Nausea is feeling an urge to vomit. It is often called "being sick to your stomach. "Vomiting or throwing-up forces the contents of the stomach up t...
Read Article Now Book Mark Article
Symptoms in newborns and younger infants may not be as easy to recognize:
- Body stiffness
- Irritability and crying more often (these symptoms may get worse when the baby is picked up)
- Poor feeding
- Soft spot on the top of the head may bulge out more
- Vomiting
Emergency symptoms:
- Loss of consciousness, poor responsiveness, stupor, coma
- Muscle weakness or paralysis
- Seizures
Seizures
A seizure is the physical changes in behavior that occurs during an episode of specific types of abnormal electrical activity in the brain. The term ...
Read Article Now Book Mark Article - Severe headache
- Sudden change in mental functions, such as flat mood, impaired judgment, memory loss, or a lack of interest in daily activities
Exams and Tests
The health care provider will perform a physical exam and ask about symptoms.
Tests that may be done include:
- Brain MRI
Brain MRI
A head MRI (magnetic resonance imaging) is an imaging test that uses powerful magnets and radio waves to create pictures of the brain and surrounding...
Read Article Now Book Mark Article - CT scan of the head
CT scan of the head
A head computed tomography (CT) scan uses many x-rays to create pictures of the head, including the skull, brain, eye sockets, and sinuses.
Read Article Now Book Mark Article - Single-photon emission computed tomography (SPECT)
- Culture of cerebrospinal fluid (CSF), blood, or urine (however, this test is rarely useful)
- Electroencephalogram (EEG)
EEG
An electroencephalogram (EEG) is a test to measure the electrical activity of the brain.
Read Article Now Book Mark Article - Lumbar puncture and CSF examination
Lumbar puncture
Cerebrospinal fluid (CSF) collection is a test to look at the fluid that surrounds the brain and spinal cord. CSF acts as a cushion, protecting the b...
Read Article Now Book Mark ArticleCSF examination
Cerebrospinal fluid (CSF) analysis is a group of laboratory tests that measure chemicals in the cerebrospinal fluid. CSF is a clear fluid that surro...
Read Article Now Book Mark Article - Tests that detect antibodies to a virus (serology tests)
- Test that detects tiny amounts of virus DNA (polymerase chain reaction -- PCR)
Treatment
The goals of treatment are to provide supportive care (rest, nutrition, fluids) to help the body fight the infection, and to relieve symptoms.
Medicines may include:
- Antiviral medicines, if a virus caused the infection
- Antibiotics, if bacteria are the cause
- Antiseizure medicines to prevent seizures
- Steroids to reduce brain swelling
- Sedatives for irritability or restlessness
- Acetaminophen for fever and headache
If brain function is severely affected, physical therapy and speech therapy may be needed after the infection is controlled.
Outlook (Prognosis)
The outcome varies. Some cases are mild and short, and the person fully recovers. Other cases are severe, and permanent problems or death is possible.
The acute phase normally lasts for 1 to 2 weeks. Fever and symptoms gradually or suddenly disappear. Some people may take several months to fully recover.
Acute
Acute means sudden. Acute symptoms appear, change, or worsen rapidly. It is the opposite of chronic.
Read Article Now Book Mark ArticlePossible Complications
Permanent brain damage may occur in severe cases of encephalitis. It can affect:
- Hearing
- Memory
- Muscle control
- Sensation
- Speech
- Vision
When to Contact a Medical Professional
Go to the emergency room or call 911 or the local emergency number if you have:
- Sudden fever
- Other symptoms of encephalitis
Prevention
Children and adults should avoid contact with anyone who has encephalitis.
Controlling mosquitoes (a mosquito bite can transmit some viruses) may reduce the chance of some infections that can lead to encephalitis.
- Apply an insect repellant containing the chemical, DEET when you go outside (but DO NOT use DEET products on infants younger than 2 months).
- Remove any sources of standing water (such as old tires, cans, gutters, and wading pools).
- Wear long-sleeved shirts and pants when outside, especially at dusk.
Children and adults should get routine vaccinations for viruses that can cause encephalitis. People should receive specific vaccines if they are traveling to places such as parts of Asia, where Japanese encephalitis is found.
Vaccinate animals to prevent encephalitis caused by the rabies virus.
Reviewed By
Charles I. Schwartz MD, FAAP, Clinical Assistant Professor of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, General Pediatrician at PennCare for Kids, Phoenixville, PA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
Beckham JD, Tyler KL. Encephalitis. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 89.
Bronstein DE, Glaser CA. Encephalitis and meningoencephalitis. In: Cherry JD, Harrison GJ, Kaplan SL, Steinbach WJ, Hotez PJ, eds. Feigin and Cherry's Textbook of Pediatric Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier; 2019:chap 36.
Lissauer T, Carroll W. Infection and immunity. In: Lissauer T, Carroll W, eds. Illustrated Textbook of Paediatrics. 6th ed. Philadelphia, PA: Elsevier; 2022:chap 15.