According to the Centers for Disease Control and Prevention (CDC), encephalitis occurs in approximately 0.5 in every 1000,000 individuals, most of them children, elderly people and individuals with weakened immune systems.
The NHS (National Health Service) NHS, UK places the figure at 1.5 cases per 100,000 people. Health authorities suspect incidence is higher than official figures because many cases go unreported when symptoms are mild.
Contents of this article:
Fast facts on encephalitis
Here are some key points about encephalitis. More detail and supporting information is in the main article.
- Encephalitis can be autoimmune or viral in origin.
- Early symptoms are fever, photophobia and headache.
- Encephalitis is rarely life-threatening.
- Encephalitis most often affects children, elderly people and those with compromised immune systems.
- Diagnosis of encephalitis can be challenging.
- Only a handful of antiviral medications can help treat encephalitis.
- Complications of encephalitis can include epilepsy and memory loss.
- Mosquitoes can carry encephalitis causing viruses.
What is encephalitis?
Encephalitis is an acute inflammation of the brain.
Encephalitis is acute inflammation (swelling up) of the brain resulting either from a viral infection or when the body's own immune system mistakenly attacks brain tissue. The most common cause is a viral infection. In medicine acute means it comes on abruptly; of abrupt onset, develops rapidly, and usually requires urgent care. Encephalitis occurs in 1 in every 1,000 cases of measles.
Encephalitis generally begins with fever and headache. The symptoms rapidly worsen, and there may be seizures (fits), confusion, drowsiness and loss of consciousness, and even coma.
Encephalitis can be life-threatening, but this is very rare.
When there is direct viral infection of the brain or spinal cord it is called primary encephalitis. Secondary encephalitis refers to an infection which started off elsewhere in the body and then spread to the brain.
Symptoms of encephalitisThe affected patient typically has a fever, headache and photophobia (excessive sensitivity to light). There may also be general weakness and seizures.
Less common - the individual may also experience nuchal rigidity (neck stiffness), which can lead to a misdiagnosis of meningitis. There may be stiffness of the limbs, slow movements, and clumsiness. The patient may also be drowsy and have a cough.
The brain swells (becomes inflamed) as a result of the body's attempt to fight off the infections.
In more severe cases, the person may experience very severe headaches, nausea, vomiting, confusion, disorientation, memory loss, speech problems, hearing problems, hallucinations, as well as seizures and possibly coma. In some cases the patient can become aggressive.
Signs and symptoms in infants (small babies) - encephalitis is harder to initially detect in infants. Parents or guardians should look out for vomiting, a bulging fontanel (soft area on the top center of the head), incessant crying that does not get better when the baby is picked up and comforted, and body stiffness.
Causes of encephalitisEncephalitis can develop as a result of a direct infection to the brain by a virus, bacterium or fungus (infectious encephalitis, or primary encephalitis), or when the immune system responds to a previous infection; the immune system mistakenly attacks brain tissue (secondary encephalitis, or post-infectious encephalitis).
Primary (infectious) encephalitis: according to the NHS (UK), there are three main categories of viruses: 1. Common viruses, such as HSV (herpes simplex virus) or EBV (Epstein Barr virus). 2. Childhood viruses, such as measles and mumps. 3. Arboviruses, which are spread by mosquitoes, ticks and other insects, and include Japanese encephalitis, West Nile encephalitis and tick borne encephalitis.
Secondary (post-infectious) encephalitis: could be caused by a complication of a viral infection. Symptoms start to appear days and even weeks after the initial infection. The patient's immune system treats healthy brain cells as foreign organisms that need to be destroyed, and attacks them. We don't know why the immune system goes wrong and does this.
Encephalitis is more likely to affect children, elderly people, individuals with weakened immune systems, and people who live in areas where mosquitoes and ticks that spread specific viruses are common.
On the next page, we look at the diagnosis and treatment of encephalitis.