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Encephalitis is irritation and swelling (inflammation) of the brain, most often due to infections.
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 viral infection. Many types of viruses may cause it. Exposure to viruses can occur through:
Breathing in respiratory droplets from an infected person
Contaminated food or drink
Mosquito, tick, and other insect bites
Different viruses occur in different 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:
Other viruses that cause encephalitis include:
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:
Parasites such as roundworms,
, and in AIDS patients and other people who have a weakened immune system
- The effects of cancer
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:
Other symptoms include:
Symptoms in newborns and younger infants may not be as easy to recognize:
- Loss of consciousness, poor responsiveness, stupor, coma
- Severe headache
- Sudden change in mental functions, such a flat mood, impaired judgment, memory loss, or a lack of interest in daily activities
Exams and Tests
An examination may show:
Tests may include:
The goals of treatment are to provide supportive care (rest, nutrition, fluids) to help the body fight the infection, and to relieve symptoms.
Medications may include:
Antiviral medicines, if a virus caused the infection
Antibiotics, if bacteria is 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.
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.
Permanent brain damage may occur in severe cases of encephalitis. It can affect:
When to Contact a Medical Professional
Go to the emergency room or call the local emergency number (such as 911) if you have:
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.
Beckham JD, Tyler KL. Encephalitis. In: Bennett JE, Dolin R, Mandell GL, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 91.
Simon DW, Da Silva YS, Zuccoli G, Clark RSB. Acute encephalitis. Crit Care Clin. 2013;29:259-277.
- Last reviewed on 8/30/2014
- Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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This page was last updated: May 5, 2015