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Definition Return to top
Encephalitis is irritation and swelling (inflammation) of the brain, usually due to infections.
See also: Meningitis
Causes Return to top
Encephalitis is most often caused by a viral infection. Many types of viruses may cause it. Exposure to viruses can occur through:
In rural areas, arboviruses -- carried by mosquitoes or ticks, or accidentally ingested -- are the most common cause.
In urban areas, enteroviruses are most common, including:
Other viruses that can cause encephalitis include:
AIDS patients and others at high-risk can develop encephalitis due to parasites such as:
Although most forms of encephalitis are caused by viruses, the condition may also be caused by bacterial diseases, such as:
Extremely rarely, an allergic reaction to vaccinations can cause encephalitis. Autoimmune disease and the effects of cancer can also cause encephalitis.
Encephalitis is uncommon. The elderly and infants are more vulnerable and may have a more severe case of the disease.
Symptoms Return to top
When the virus enters the bloodstream, it may cause inflammation of brain tissue and surrounding membranes. White blood cells invade the brain tissue as they try to fight off the infection. The brain tissue swells (cerebral edema), which may destroy nerve cells, cause bleeding in the brain (intracerebral hemorrhage), and brain damage.
Exams and Tests Return to top
An examination may show:
Tests may include:
Treatment Return to top
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:
If brain function is severely affected, interventions like physical therapy and speech therapy may be needed after the illness is controlled.
Outlook (Prognosis) Return to top
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.
Possible Complications Return to top
Permanent brain damage may occur in severe cases of encephalitis. It can affect:
When to Contact a Medical Professional Return to top
Go to the emergency room or call the local emergency number (such as 911) if you have:
Prevention Return to top
Controlling mosquitoes (a mosquito bite can transmit some viruses) may reduce the chance of some infections that can lead to encephalitis.
Vaccinate animals to prevent encephalitis caused by the rabies virus.
Human vaccinations that are available include:
References Return to top
Bleck TP. Arthropod-borne viruses affecting the central nervous system. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 406.
Modlin JF. Enterovirus infections. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 402.
Nath A. Berger JR. Acute viral encephalitis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 439.
Whitley RJ. Herpes simplex virus infections. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 397.Update Date: 9/28/2008 Updated by: Jatin M. Vyas, PhD, MD, Instructor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.