Encephalitis is a swelling of the brain tissue that can be very serious, sometimes causing death. Although people often recover fully within a couple of weeks, others (especially children and older people) may have permanent problems, including seizures, memory loss, personality changes or brain damage. The chances of dying from the disease or having permanent problems after recovery depend on the cause, seriousness, the person's age and how quickly the illness developed.


The condition usually starts with sudden fever and a severe headache. 

Other signs include:

  • Abnormal sensitivity to light
  • Nausea and vomiting
  • Stiff neck and back
  • Lack of energy, feeling sluggish
  • Drowsiness
  • Seizures or tremors (shaking)
  • Personality change
  • Loss of memory
  • Trouble learning and understanding
  • Restlessness, confused speech, confused thinking
  • Coma


Causes and Risk Factors

Cold sores and genital herpes, mumps, measles, chickenpox, Epstein-Barr virus, flu and German measles are possible risk factors for encephalitis. These viruses usually cause less serious illnesses, but in rare cases they can get into the brain and cause encephalitis. Another group of viruses is mainly the result of mosquito and tick bites.

Infection with the rabies virus can also cause encephalitis and is almost always fatal if not treated before symptoms show up. People who have weak immune systems, especially those with AIDS, are at higher risk for getting encephalitis from infections.


The most important test in discovering the disease is a spinal tap to study the fluid in the spine. For this procedure, a needle is inserted in the lower back between the bones of the spine. The spinal fluid is checked for infection. In certain cases, doctors look for traces of the herpes simplex virus (the cause of some cold sores or genital herpes).

Blood tests can help identify specific causes, while imaging procedures can confirm a diagnosis. An MRI (magnetic resonance imaging) scan may be used to take a picture of the brain to look for signs of bleeding, swelling or other changes. An EEG scan (electroencephalography) records the brain's electrical patterns, possibly revealing abnormal activity in the brain.

A brain biopsy (taking a small sample of tissue for examination) is sometimes used to find the cause. A biopsy can be especially helpful if herpes simplex encephalitis is suspected and the patient does not improve after taking a drug to fight the virus. A brain biopsy is not used very often because tests on spinal fluid can accurately diagnose the condition caused by the herpes simplex virus.


Viruses carried by mosquitoes and ticks cannot be destroyed with drugs. Doctors use medications to keep the patient comfortable and allow the body to heal itself.