Encephalitis is a complex and severe disease that can occur in people of all ages anywhere in the world. It is defined as an inflammation of the brain substance together with evidence of brain dysfunction.
Inflammation has occurred in the brain because something foreign or something abnormal has sparked the immune system into action. This action has resulted in the inflammation.
Some types of encephalitis can be mild and produce almost no symptoms, just a general feeling of being unwell accompanied by a fever. Other cases can be very serious and life threatening.
There are two main types of encephalitis; Infectious Encephalitis and Autoimmune Encephalitis. Both have many different causes but sometimes the underlying reason for the illness cannot be explained. Worldwide it has been estimated that around 40% of encephalitis cases are infectious, 40% are due to unknown causes and at least 20% are autoimmune.
Infectious Encephalitis, also called Primary Encephalitis, is a direct result of an organism (germ) infecting the brain, most often this is a virus. The brain is strongly protected against viruses and other germs, which is why encephalitis is rare. Other types of germs that cause of encephalitis are bacteria, especially small bacteria, fungi and parasites. Sometimes the infection occurs in a small area of the brain (a focal infection) but often it spreads to many different areas (a diffuse infection). The infection is usually short lived (acute) but very rare, longer lived and persistent (chronic ) forms are known.