Children, the elderly, and those with a weak immune system are most vulnerable. The disease is usually caused by one of several viral infections, so it's sometimes referred to as viral encephalitis.
Many people who have encephalitis fully recover. The most appropriate treatment and the patient's chance of recovery depend on the virus involved and the severity of the inflammation.
In acute encephalitis, the infection directly affects the brain cells. In para-infectious encephalitis, the brain and spinal cord become inflamed within one to two weeks of contracting a viral or bacterial infection.
Herpes simplex type 1 virus is one of the more common and serious causes of viral encephalitis. Herpes-related encephalitis can erupt rapidly, and may cause seizures or mental changes and even lead to coma or death. It occurs when the herpes simplex type 1 virus travels to the brain rather than moving through the body to the surface of the skin and producing its more common symptom, a cold sore. Early recognition and treatment of herpes encephalitis can be life-saving. You are not more likely to get encephalitis if you have cold sores.
Arbovirus encephalitis is another form of viral encephalitis. It is caused by various viruses that are carried by insects (such as mosquitoes and ticks). Unlike herpes, arboviral infections are seasonal, occurring primarily in summer and early fall, and are clustered in specific regions, such as in the case of St. Louis encephalitis.
In rare instances, bacterial, fungal, parasitic, or rickettsial infections cause encephalitis. Cancer or even exposure to certain drugs or toxins may also cause encephalitis.