Encephalitis Causes & Risks

Causes

Viral infection of the central nervous system can be asymptomatic, present with mild symptoms, or cause meningitis and/or encephalitis. Most cases of encephalitis are caused by a viral infection. Encephalitis may be sporadic or epidemic. In the United States, the most common cause of sporadic encephalitis is the herpes simplex virus . Epidemic encephalitis are usually mosquito - or tick-borne, which may be dependant on the geography and season.

The most common viruses that cause encephalitis include:

Viruses carried by mosquitoes such as West Nile virus
Chickenpox virus
Herpes simplex virus
Polio virus
Epstein-Barr virus
Measles virus
Mumps virus
Rotavirus
Influenza virus
Rabies
Enterovirus

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. Risk factors for encephalitis include:

Living, working, or playing in an area where mosquito-borne viruses are common
Not being immunized against diseases such as:
- Measles
- Mumps
- Chickenpox
- Polio
Having cancer
Taking immunosuppressive medications after organ transplant
Having AIDS

Newborns of mothers who have genital herpes simplex are at risk for herpes simplex encephalitis.

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition. Copyright © 2026 EBSCO Publishing All rights reserved.