If you need to define a word in your paper, the definition usually comes from a glossary in the back of a book. To properly attribute this definition you will need to cite it according to the American Psychological Association (APA) style guidelines.
Encephalitis is inflammation of the brain tissue. It's most often caused by viral infections. In some cases, bacterial infections can also cause encephalitis.
In the UK, the most common virus to cause encephalitis is herpes simplex virus. Symptoms usually start with the common symptoms of a viral infection such as high temperature (fever), headache, muscle aches, feeling tired and feeing sick (nausea). Confusion, drowsiness and eventually coma can develop.