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.
Secondary (post-infectious) encephalitis: could be caused by a complication of a viral infection. Symptoms start to appear days or even weeks after the initial infection. The patient's immune system treats healthy brain cells as foreign organisms and attacks them.