A viral infection that often causes minimal if any symptoms. When symptoms occur, most often they are flu-like. Occasionally, the virus causes inflammation of the lining around the brain and spinal cord (aseptic meningitis) and/or inflammation of the brain (encephalitis). The virus lives in wild birds. Mosquitoes get the virus after biting an infected bird. People then acquire the virus after being bitten by an infected mosquito. The risk of becoming infected is highest during the mosquito season. Efforts to decrease the mosquito population can reduce the number of infections. Most patients fully recover and death is extremely rare. The elderly and people with impaired immune systems have a higher risk of complications and death.