Herpes encephalitis, a rapidly progressing disease, is the single most important cause of fatal sporadic encephalitis in the United States. This disease, which is caused by herpes simplex virus type 1, can affect any age group, but is most often seen in people under age 20 or over age 40. More than half of all untreated cases are fatal.
Herpes encephalitis is responsible for about 10 percent of all encephalitis cases. There are about two cases of herpes encephalitis per million people per year.
This rapidly progressing disease is the single most important cause of fatal sporadic encephalitis in the United States.
Herpes encephalitis can be due to either the herpes simplex virus type 1 or herpes simplex virus type 2. Cases due to herpes simplex virus type 1 (which causes cold sores or blisters around the mouth or eyes) can affect any age group, but is most often seen in people under age 20 or over age 40.
About 30 percent of cases of herpes encephalitis result from the initial infection with the herpes simplex virus; the majority of cases are caused by reactivation of an earlier infection.
Herpes encephalitis caused by the type 1 virus is transmitted through contact with an infected person.
Type 2 virus (genital herpes) is most often transmitted through sexual contact. An infected mother can transmit the disease to her child at birth (through contact with genital secretions), but this is uncommon.