Encephalitis is inflammation of the brain. Inflammation changes the normal blood flow in the brain.

Infection with a virus is the main cause of encephalitis. The herpes simplex virus is a common cause in North America. This is the same virus that causes cold sores and genital herpes. The viruses that cause mumps, measles, chicken pox, mono (Epstein-Barr virus), influenza, and German measles (rubella) also can cause encephalitis. But these viruses only rarely infect the brain and cause encephalitis.

Another group of viruses, called arboviruses, can spread encephalitis through bites from mosquitoes and ticks. West Nile virus is one of these viruses. But most people who are bitten by infected mosquitoes or ticks do not get any symptoms. And only a very small number of people who have symptoms get encephalitis.

Infection with the rabies virus is a form of encephalitis, but this is very rare.

Symptoms of encephalitis can be mild or very serious. Symptoms can include:

  • Confusion.
  • A fever.
  • headache (which can be very painful).
  • A stiff neck and back.
  • Light hurting your eyes.
  • Nausea and vomiting.
  • Lack of energy.
  • Drowsiness.

More serious symptoms include:

  • Seizures.
  • Tremors.
  • Personality changes.
  • Memory loss.
  • Hallucinations (seeing or hearing things that aren’t there).

Early on, symptoms of encephalitis may be like those of meningitis. This is a serious viral or bacterial illness that causes swelling of the tissues around the brain and spinal cord.

Encephalitis is rare, but it can be deadly. If you think you or your child have symptoms of encephalitis, see a doctor right away.

Your chance of getting encephalitis is low. But you can reduce your chance of getting it even more.

  • Make sure that you and your children get vaccines against measles, mumps, rubella, chicken pox, and the flu.
  • Avoid areas where there has been an outbreak of viral encephalitis. If you cannot avoid these areas:
    • Stay indoors at dawn and dusk. Mosquitoes are most active at these times.
    • Wear long-sleeved shirts and long pants when you go outdoors.
    • Don’t wear floral scents from perfumes, soaps, hair care products, and lotions. These may attract mosquitoes.
    • Spray clothing with an insect repellent containing permethrin or DEET to prevent mosquitoes from biting through clothing. An effective repellent will contain 24% DEET. Don’t apply repellent to the hands of children. Repellents may irritate the eyes and mouth.
    • Don’t use old tires as swings or play equipment or keep them on your property for other reasons. When old tires collect water, they become breeding grounds for mosquitoes.

Doctors usually diagnose encephalitis by testing the fluid in the spine for increases in white blood cells and protein. An MRI scan, which takes pictures of the inside of your body, may show bleeding, swelling, or other changes in the brain. Another test, called an EEG, can measure the electrical signals in the brain. It may show a change related to the illness.

You also may have blood tests to find out what type of virus is causing encephalitis. In some cases, a sample of brain tissue (biopsy) might be tested to look for infection.

Most people recover if they are treated promptly. But the illness can sometimes cause long-term problems, such as trouble with speech or memory.

If you have encephalitis, you will need to be treated in a hospital. Your treatment will depend on your symptoms and the cause of your illness. For example, if the herpes simplex virus or chicken pox virus is the cause, you will get medicine called acyclovir. This medicine can stop viruses. But it works best if you get it right away.

There is no antiviral medicine to treat encephalitis caused by viruses spread by mosquitoes or ticks. Instead, you would get care to ease your symptoms and allow your body to heal on its own. This is called supportive care. You may take medicines to reduce pain and fever or to stop seizures. In some cases, you may need a ventilator to help you breathe.