Risk factors

By Mayo Clinic Staff

Anyone can develop encephalitis. Factors that may increase the risk of the condition include:

  • Age. Some types of encephalitis are more prevalent or more severe in certain age groups. In general, young children and older adults are at greater risk of most types of viral encephalitis. Encephalitis from the herpes simplex virus tends to be more common in people 20 to 40 years of age.
  • Weakened immune system. People who have HIV/AIDS, take immune-suppressing drugs, or have another condition causing a compromised or weakened immune system are at increased risk of encephalitis.
  • Geographic regions. Mosquito-borne or tick-borne viruses are common in particular geographic regions.
  • Season of the year. Mosquito- and tick-borne diseases tend to be more prevalent in spring, summer and early fall in many areas of the United States. In warmer areas of the U.S., however, mosquitoes and ticks may be present year-round.
May 15, 2014