| Risk Factors is inflammation of the brain. Certain mosquito-
borne viruses can lead to encephalitis. Examples of these
viruses include: - West Nile encephalitis - Eastern equine
encephalitis - Western equine encephalitis - St. Louis
encephalitis - La Crosse encephalitis - Japanese encephalitis -
Venezuelan equine encephalitis Copyright © Nucleus Medical
Media, Inc. The most common cause is being bitten by an infected
mosquito. There are other, rarer causes, such having a with
infected blood. The greatest risk factors are spending time in
areas where mosquitoes are present and not using insect
repellent. People who are age 50 years and older and those with
a weakened immune system have a higher risk of developing
serious symptoms. Most people who become infected with one of
these mosquito-borne viruses do not develop any symptoms. If
symptoms do occur, they are generally mild and may include flu-
like symptoms, such as: - Joint and muscle pain While rare, a
small percentage of people develop encephalitis and h