While the etiology of many cases of encephalitis is unknown, viruses account for about 70% of confirmed encephalitis cases, with the herpes simplex virus being the most common cause at about 50% of encephalitis cases. The incidence of<unk>  is about 3.5 to 7.5 per 100,000 people, with the highest incidence among the young and the elderly.<unk>  caused by some viruses, such as the measles virus and the mumps virus, has become less common due to widespread vaccination. For others, such as Epstein-Barr virus and cytomegalovirus, incidence has increased due to the increased prevalence of AIDS, organ transplantation, and chemotherapy, which have increased the number of immunocompromised people who have weakened immune systems or who are susceptible to opportunistic infections. Time of the year, geography, and animal, including insect, exposure are also important. For example, arbovirus infections are seasonal and cause<unk>  at the highest rate during the summer and early fall when mosquitos are most active. Similarly, those who live in warm, humid climates where there are more mosquitos are more likely to experience<unk> .
Viral encephalitis
Anti-NMDA receptor encephalitis
Herpesviral encephalitis
Anti-Hu associated encephalitis
Powassan encephalitis
Autoimmune encephalitis
Fungal meningitis
Viral meningitis