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.
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).