Herpes simplex encephalitis (HSE) is a rare neurological disorder characterized by inflammation of the brain. It is caused by the herpes simplex virus type I (HSV I). Occasionally, it is possible for the virus to move to the brain from the nasal cavity through the sinuses. This can result in encephalitis.

Common symptoms include:

• Headaches
• Fevers
• Drowsiness
• Hyperactivity
• Weakness

Other symptoms such as a stiff neck, altered reflexes, confusion, and/or speech abnormalities can occur as well.
As the disease progresses more serious symptoms are likely. These include personality changes, paralysis, hallucinations, convulsions, and even coma can occur. With treatment, the death rate is greatly reduced; however there may be permanent neurological problems. If left untreated, herpes encephalitis can result in death.