Encephalitis is a swelling of the functional parts of the brain that can be caused by specific viruses or by an autoimmune response. This can have serious and long-lasting effects; prevention is therefore the key.

Viral encephalitis

Most cases of encephalitis are caused by viral infections. Many viruses can cause inflammation and can reach the central nervous system (CNS) via the neurons that link various parts of the body with the brain or through the neurons of the nose. The following are most commonly associated with such acute viral encephalitis:

  • Herpes simplex virus, the virus responsible for cold sores
  • Human herpes viruses, including the chicken pox and measles virus
  • Rubella virus, which causes German measles and can spread to the brain several years later, causing sub-acute sclerosing panencephalitis (SSPE)
  • West Nile fever virus, an arbovirus spread by mosquitoes in Africa, Europe, the Middle East, Asia, and North America
  • Japanese encephalitis virus, which is particularly prevalent across Asia and Australia and is spread by mosquitoes
  • The human immunodeficiency virus (HIV)
  • Rabies virus, spread by bites from infected animals; common in south and south-east Asia

Although these viruses can be spread by either human-to-human contact or by the bite of a mosquito, encephalitis itself cannot be spread from one person to another.

Post-viral encephalitis

Encephalitis can also be a result of the immune system attacking the brain after a viral infection and is termed post-infectious, or autoimmune encephalitis. In most cases, we do not fully understand why this happens. Several forms exist:

  • Acute disseminated encephalomyelitis (ADEM) arises following viral infection, rash, or immunisation, but is not caused by a virus.
  • Hashimoto’s encephalitis, a condition in which antibodies attack the body’s own nerve cells in the brain. It is a rare complication of the autoimmune thyroid disease, Hashimoto’s thyroiditis.
  • Rasmussen’s syndrome, which causes inflammation of specific parts of the brain.

The symptoms of encephalitis

Encephalitis can develop extremely quickly and symptoms vary depending on the stage of infection. The early signs of inflammation include:

  • Headaches
  • Increased body temperature
  • Just not feeling ‘well’

Symptoms then develop over a period of days or weeks to resemble those of influenza and can include:

  • Feeling tired more than usual or getting very drowsy.
  • A sore throat.
  • Having a stiff and painful back or neck.
  • Getting confused or irritated with those around you.
  • Stumbling and having trouble walking.
  • Finding it uncomfortable to be in a brightly lit room.

Diagnosing encephalitis

Because this is a very specific type of brain inflammation, it is important to distinguish it from other neurological conditions that have similar symptoms but need to be treated differently. The following tests are carried out to do this:

  • Brain scans, including computerised tomography (CT) or magnetic resonance imaging (MRI).
  • An electroencephalogram (EEG) to check the function of the brain.
  • A lumbar puncture, in which a doctor removes a small amount of cerebrospinal fluid (or CSF), the fluid that surrounds the brain and spinal cord, to check for infections.

It is also important to find out if the person affected has recently travelled to regions of the world that have a high risk of acute viral encephalitis.

Anyone can be affected by encephalitis, although young children and the elderly are at the highest risk. The earlier the encephalitis is diagnosed, the better the outcome.