Jamestown Canyon virus: a mosquito-transmitted virus found throughout the United States, predominantly reported in the upper Midwest. The infection can cause symptoms including fever, headache, and fatigue, but many people can get infected with the virus and not have symptoms. Most cases occur from late spring through mid-fall. Typical time to the development of symptoms is a few days to 2 weeks after the mosquito bite. In rare instances, Jamestown Canyon virus leads to severe disease, including encephalitis (infection of the brain) or meningitis (infection of the tissues lining the brain).