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Herpes simplex virus type 1 encephalitis

Robyn S Klein, MD, PhD
Section Editor
Martin S Hirsch, MD
Deputy Editor
Jennifer Mitty, MD, MPH


Herpes simplex virus type 1 (HSV-1) encephalitis is the most common cause of sporadic fatal encephalitis worldwide. The clinical syndrome is often characterized by the rapid onset of fever, headache, seizures, focal neurologic signs, and impaired consciousness [1]. HSV-1 encephalitis is a devastating disease with significant morbidity and mortality, despite available antiviral therapy.

The pathogenesis, clinical manifestations, diagnosis, and treatment of HSV-1 encephalitis will be reviewed here. Neonatal encephalitis and other manifestations of HSV-1 infection are discussed separately. (See "Clinical manifestations and diagnosis of herpes simplex virus type 1 infection".)


HSV-1 encephalitis is the most common cause of fatal sporadic encephalitis in the United States, accounting for approximately 10 to 20 percent of the 20,000 annual viral encephalitis cases [2,3]. The infection arises in all age groups, with one-third of all cases occurring in children and adolescents [4]. HSV is also the most commonly identified pathogen among hospitalized patients diagnosed with encephalitis in Australia [5]. In a nationwide retrospective study of the incidence of HSV-1 encephalitis in Sweden over a 12-year period (1990 to 2001), the incidence of confirmed cases was 2.2 per million population per year [6].


In nearly all cases of herpes encephalitis beyond the neonatal period, the etiologic agent is herpes simplex virus type 1 (HSV-1). In neonates, herpes encephalitis may be caused by either HSV-1 or HSV-2.

HSV-2 produces a more global encephalitis with significant neurologic impairment. In one series of 24 infants with HSV encephalitis and a mean follow-up of 19 months, only 4 of 14 (28 percent) survivors with HSV-2 encephalitis were neurologically normal compared to nine of nine infants with HSV-1 [7].


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Literature review current through: Sep 2016. | This topic last updated: Aug 15, 2014.
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