Acute inflammation of the brain (a reaction of the immune system), typically due to viral infection sometimes transmitted by mosquitoes or arising as a consequence of lead poisoning, but assuming a number of different types. When it involves the spinal cord as well, it is referred to encephalomyelitis. It can also occur as a complication of the likes of chickenpox, herpes simplex, influenza, measles, mumps, and rabies. Signs include fever, headache, nausea, neck pain, and neurological insults such as convulsions and paralysis, as well as coma leading to death. In the US, about 2000 cases of encephalitis are reported each year. There is also another form of externally-induced encephalitis known as chronic traumatic encephalitis. It is most evident in boxers and presents with mood, movement and cognitive problems (hence it was previously referred to dementia pugilistica). It also been reported in people who participate in soccer (through repeatedly heading a ball), American football, hockey and wrestling.
See Hippocampus, Meningitis, Spinal cord