What is encephalitis?

Encephalitis is an uncommon but serious disease that causes swelling in the brain. It can affect anyone of any age but it is more common if you have low immunity, or if you are elderly or very young. 

Encephalitis can be life threatening with serious long-lasting effects and therefore needs immediate medical attention. 

You can develop encephalitis if you have a viral infection that reaches the central nervous system (CNS) and brain.

Many viruses can cause primary (acute) viral encephalitis. The most common include:

• Herpes simplex virus e.g HSV 1 and HSV 2) 
• Other herpes viruses e.g. varicella-zoster (chicken pox), morbillivirus and paramyxoviridae (measles), epstein-barr
• Enteroviruses (coxsackie and polioviruses) 
• Rubella virus (German measles)
• Mosquito borne viruses (West Nile virus, La Crosse, St Louis and Japanese encephalitis)
• Tick borne viruses (Powassan virus)
• Human immunodeficiency virus (HIV) 
• Rabies lyssavirus (rabies) spread by bites from infected animals

Although viruses can cause encephalitis, you cannot catch encephalitis from another human being.

What is post-infection encephalitis?

Post infection encephalitis (autoimmune encephalitis) occurs when your immune system starts to attack healthy nerve cells (neurones) in the brain. 

Autoimmune (secondary) encephalitis develops when your immune system mistakenly attacks healthy brain cells as well as infected cells elsewhere in your body. 

Post-infection encephalitis normally develops two to three weeks after a viral infection. 

It’s not fully clear why this happens, but there are several forms:

• Acute disseminated encephalomyelitis (ADEM) following a viral infection, rash or immunisation
• Hashimoto’s encephalitis in which your immune system attacks the nerve cells (neurones) in the brain as a rare complication of autoimmune thyroiditis (Hashimoto’s thyroiditis)
• Ramussen’s syndrome which causes inflammation in specific parts of the brain

What are the symptoms of encephalitis?

Encephalitis can develop very quickly and symptoms vary depending on the stage of infection. 

The early signs of encephalitis are similar to flu and include:

• Headaches
• Increased body temperature
• Aches in the muscles or joints
• Fatigue or weakness

More severe symptoms may develop over a period of days or weeks including:

• Drowsiness and confusion
• Stiff and painful back or neck
• Intolerance to bright light
• Loss of sensation or paralysis in parts of the face or body
• Problems with speech 
• Problems with hearing
• Problems with movement
• Seizures
• Hallucinations
• Loss of consciousness

In children and infants signs and symptoms can include: 

• Bulging in the soft spot of the head (fontanels)
• Body stiffness 
• Difficulty feeding
• Irritability
• Poor sleep or excessive sleep

How is encephalitis diagnosed?

Your specialist will make a diagnosis based on your symptoms and medical history. 

They will also want to know if you’ve recently been abroad to countries where acute viral encephalitis is more common.

They will send you for a number of brain scans and test to confirm if you have encephalitis:

• Computerised tomography (CT) 
• Magnetic resonance imaging (MRI) 
• Electroencephalogram (EEG) 
• Lumbar puncture to remove a small amount of cerebrospinal fluid (CSF) that surrounds the brain and spinal cord
• If you think you might have encephalitis it’s important to seek medical help right away

The earlier you can start treatment the better your overall outcome will be.