Boots WebMD Partners in Health
Return To Boots

Encephalitis: Symptoms, diagnosis and treatment

What is encephalitis?

Encephalitis is a serious condition causing inflammation of the brain. The condition is rare, affecting around 4,000 people in the UK each year.

In its early stages, encephalitis has flu-like symptoms, including fever, headache and joint pain.

Over some days or hours, other more severe symptoms develop. These include seizures, personality changes, confusion, drowsiness or disorientation.

There are several causes of encephalitis, including infectious, delayed reactions to previous infections and the body's immune system reacting to changes such as a cancer tumour.

Another type of the condition is chronic encephalitis where the inflammation develops over many months. Sometimes no cause is found, but in other cases, conditions like HIV may be responsible.

Encephalitis is a medical emergency usually needing treatment in a hospital intensive care unit.

Recovery can take many months and lasting complications are possible, including memory loss.

What causes encephalitis?


Viral encephalitis may develop during or after infection with any of several viral illnesses including influenza, herpes simplex, measles, mumps, rubella, rabies, chickenpox and arbovirus infection including West Nile virus and Japanese encephalitis.

Herpes simplex virus is one of the more common and serious causes of viral encephalitis. Herpes-related encephalitis can develop rapidly, and may cause seizures or mental changes and even lead to coma or death. It occurs when the herpes simplex virus travels to the brain rather than moving through the body to the surface of the skin and producing its more common symptom, a cold sore. Early recognition and treatment of herpes encephalitis can be life saving. You are not more likely to get encephalitis if you have cold sores.

The other common cause of encephalitis in the UK is the varicella-zoster virus that causes chickenpox and shingles.
Arbovirus encephalitis is another form of viral encephalitis. It is caused by various viruses that are carried by insects (such as mosquitoes and ticks). Unlike herpes, arboviral infections are seasonal, occurring primarily in summer and early autumn, and are clustered in specific regions

In rare instances, bacterial, fungal, parasitic or rickettsial infections cause encephalitis. Cancer or even exposure to certain drugs or toxins may also cause encephalitis.

What are the symptoms of encephalitis?

The symptoms of encephalitis are usually sudden and severe. They include the following:

  • Fever
  • Drowsiness, lethargy and possibly coma
  • Headaches
  • Personality changes, irritability or emotional outbursts
  • Confusion
  • Weakness in one or more areas of the body
  • Seizures
  • Bulging soft spots in infants

Seek medical attention immediately if:

  • You develop sudden or severe fever, drowsiness, lethargy or headache
  • You notice personality changes, such as unusual irritability or emotional outbursts, or you become confused
  • You develop weakness in one or more areas of your body
  • You have a seizure

How do I know if I have encephalitis?

To diagnose encephalitis, your doctor will consider your symptoms and ask about any recent illnesses you've had and your possible exposure to viruses - being near others who are ill or near mosquitoes or ticks, for example.

Your doctor will refer you to a specialist who may arrange a magnetic resonance imaging (MRI) scan, lumbar puncture (spinal tap) or an electroencephalogram (EEG). Blood tests to check for the presence of bacteria or viruses and immune cells produced in response to them can also be helpful. An analysis of a brain tissue sample ( biopsy) may be necessary to confirm the diagnosis. It is very important to identify the kind of encephalitis so that appropriate treatment can be given.

WebMD Medical Reference

Stay informed

Sign up for BootsWebMD's free newsletters.
Sign Up Now!

Popular slideshows & tools on BootsWebMD

woman coughing
Home remedies for coughing
smiling baby
Causes and remedies
man holding sore neck
16 tips when you have a lot of weight to lose
mother and child
Caring for a baby with cows' milk allergy
woman holding mouth
What causes sensitive teeth?
man holding sore neck
8 signs you're headed for menopause
man holding sore neck
The best time to do everything
bain illustration
Best foods for your brain
woman doing situps
7 most effective exercises
avacado on whole wheat crackers
Plenty to choose from
egg in cup
Surprising things that can harm your liver