Our expert says:
Encephalitis is an infection of the membranes of the brain.
What is encephalitis?
Encephalitis is an inflammation of the brain that is usually the result of a viral infection. When the brain becomes inflamedâ€”swollen and irritatedâ€”normal blood flow to the brain is altered, leading to symptoms such as confusion, fever, and severe headache. Encephalitis is rare.
What causes encephalitis?
The most common cause in the United States is the herpes simplex virus, the same virus that causes cold sores and genital herpes. Other common viruses that may cause encephalitis include those that cause mumps, measles, chickenpox, mononucleosis (Epstein-Barr virus), influenza, and German measles (rubella). These viruses usually lead to less serious illnesses, but on rare occasions, they infect the brain and cause encephalitis.
Another group of viruses, called arboviruses, can spread encephalitis mainly through bites from mosquitoes and ticks. Most people who are bitten by infected mosquitoes or ticks do not develop any symptoms, and only a very small number of people who develop symptoms of infection from arboviruses actually develop encephalitis. In the U.S., encephalitis caused by arboviruses tends to occur in the summer and early fall when mosquitoes and ticks are biting and people are spending more time outdoors.
Although very rare, infection with the rabies virus can also lead to encephalitis that is almost always fatal it not treated before symptoms develop.
What are the symptoms?
The most common symptoms of encephalitis are fever, severe headache, and confusion. Other symptoms may develop, such as sensitivity to light, nausea and vomiting, stiff neck and back, and drowsiness. It is also possible to develop severe symptoms such as seizures, tremors, personality changes, and even coma.
In general, symptoms that develop suddenly and are severe from the start usually indicate more serious, life-threatening encephalitis.
Early on, symptoms of encephalitis may be similar to those of meningitis, a serious viral or bacterial illness that causes inflammation of the tissues surrounding the brain and spinal cord.
How is encephalitis diagnosed?
Encephalitis is usually diagnosed by analyzing the fluid in the spine (cerebrospinal fluid) for evidence of infection, such as increases in white blood cells and protein. Samples of spinal fluid are taken during a lumbar puncture (also known as a spinal tap), in which a needle is inserted in the lower back between the bones of the spine.
Magnetic resonance image (MRI), which takes pictures of the structures inside the body, may reveal bleeding, inflammation, or other changes in certain areas of the brain, depending on what type of encephalitis you have.
An electroencephalogram (EEG), which uses small sensors (electrodes) to measure the electrical impulses in the brain, may show an abnormal change in the brain's electrical activity related to encephalitis.
Blood tests also may be used to identify the virus causing encephalitis.
Less commonly, a biopsy of brain tissue or tissue and fluid surrounding the brain may be done to look for signs of infection.
How is it treated?
In the initial stage of the illness, you likely will be treated in a hospital's intensive care unit. During your stay, your treatment and supportive care will depend upon your particular symptoms and the cause of your illness. If the herpes simplex virus or chickenpox (varicella-zoster) virus is the cause, you will be given the antiviral medication acyclovir in a vein (intravenous, or IV). The success of this treatment depends on giving acyclovir as soon as encephalitis is suspected. Some health professionals also are using the herpes zoster medication valacyclovir for herpes simplex encephalitis, even though it has not yet officially been approved for the treatment of encephalitis (unlabeled use).
No antiviral medication is available to treat encephalitis caused by viruses spread by mosquitoes or ticks. Instead, health professionals provide supportive care to reduce symptoms and allow the body to heal on its own. Such treatment may involve medications to reduce pain and fever or stop seizures. In some cases, you may need a machine (ventilator) to help you breathe.
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