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Encephalitis is irritation and swelling (inflammation) of the brain, most often due to infections.
See also: Meningitis
Causes, incidence, and risk factors
Encephalitis is a rare condition. It occurs more often in the first year of life and decreases with age. The very young and the elderly 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 will occur in different locations. Many cases will tend to cluster in a certain season.
Encephalitis caused by the herpes simplex virus is the leading cause of more severe cases in all ages, including newborns.
A number of viruses for which there is now a vaccine may also cause encephalitis. These include:
Other viruses that cause encephalitis include:
The virus causes inflammation of brain tissue. The brain tissue swells (cerebral edema), which may destroy nerve cells, cause bleeding in the brain (intracerebral hemorrhage), 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 patients may have symptoms of a cold or stomach infection before encephalitis symptoms begin.
When a case of encephalitis is not very severe, the symptoms may be similar to those of other illnesses, including:
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:
- "Flat" mood, lack of mood, or mood that is inappropriate for the situation
- Impaired judgment
- Inflexibility, extreme self-centeredness, inability to make a decision, or withdrawal from social interaction
- Less interest in daily activities
- Memory loss (amnesia), impaired short-term or long-term memory
Signs 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. Reorientation and emotional support for confused or delirious people may be helpful.
Medications may include:
Antiviral medications, such as acyclovir (Zovirax) and foscarnet (Foscavir) -- to treat herpes encephalitis or other severe viral infections (however, no specific antiviral drugs are available to fight encephalitis)
Antibiotics -- if the infection is caused by certain bacteria
Anti-seizure medications (such as phenytoin) -- to prevent seizures
Steroids (such as dexamethasone) -- to reduce brain swelling (in rare cases)
Sedatives -- to treat irritability or restlessness
Acetaminophen -- for fever and headache
If brain function is severely affected, interventions like physical therapy and speech therapy may be needed after the illness is controlled.
The outcome varies. Some cases are mild and short, and the person fully recovers. Other cases are severe, and permanent impairment or death is possible.
The acute phase normally lasts for 1 - 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:
Calling your health care provider
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 never 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, particularly at dusk.
Vaccinate animals to prevent encephalitis caused by the rabies virus.
Human vaccinations that are available include:
Aksamit AJ Jr. Acute viral encephalitis. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier;2011:chap 422.
Bleck TP. Arthropod-borne viruses affecting the central nervous system. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 391.
- Last reviewed on 8/1/2012
- Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.
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