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Cause of Encephalitis

Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is responsible for about 10 percent of all encephalitis cases, with a frequency of about two cases per million people per year. More than half of untreated herpes encephalitis cases are fatal. About 30 percent of cases result from the initial infection with the herpes simplex virus; the majority of cases are caused by reactivation of an earlier infection.
HSE 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.
This rapidly progressing disease is the single most important cause of fatal sporadic encephalitis in the United States. The virus is transmitted through contact with an infected person. Symptoms include headache and fever for up to five days, followed by:
  • Personality and behavioral changes
  • Seizures
  • Partial paralysis
  • Hallucinations and altered levels of consciousness.
Brain damage in adults and in children beyond the neonatal period is usually seen in the frontal and temporal lobes and can be severe.
The 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. In newborns, symptoms such as lethargy, irritability, tremors, seizures, and poor feeding generally develop between 4 and 11 days after delivery.

Powassan Encephalitis

Powassan encephalitis is the only well-documented tick-borne arbovirus in the United States and Canada. Symptoms are noticed 7 to 10 days following the bite and may include:
  • Headache
  • Fever
  • Nausea
  • Confusion
  • Partial paralysis
  • Coma.
Permanent neurologic damage occurs in about half of all cases and death in about 10 to 15 percent of all cases.
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Information on Encephalitis

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